Raspberry Pi Tips, Tricks & Hacks Volume 1 Second Revised Edition Tips

User Manual: Raspberry Pi Tips Tricks Hacks Volume 1 Second Revised Edition

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SD CARD

40 PINS: 28x GPIO, I2C, SPI, UART

Raspberry Pi

Practical projects Essential upgrades  Python tips

NEW

Over

Raspberry

Pi projects

Pi Zero

tricks

inside

FREE

DISTROS

The Raspberry Pi is powering a computing revolution that is sweeping the world.

It’s changed the face of the classroom forever, it’s used in amazingly creative

projects at Raspberry Jam events everywhere from Yorkshire villages to the capital

of Australia, and every weekend families get together to code, create and craft

new gadgets. Whether you’re six or sixty, there’s a Pi project for you. And that’s

where we come in. In this new edition of Raspberry Pi Tips, Tricks & Hacks we’re

giving you everything you need to not only get up and running with a brand

new Raspberry Pi, but also fire up your imagination and unleash your creativity.

From programming-based projects like tethering your Pi to an Android, through

hardware projects including digital photo frames, arcade machines and touch-

screen video players, all the way to advanced robotics projects that will see

you building your own Raspberry Pi-powered, remote control vehicles and car

computers, we’ve got plenty here to keep you busy. All you need is your favourite

$35 computer – and a passion for making things!

Welcome to

Raspberry Pi

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bookazine series

Part of the

Raspberry Pi

Contents

12 Set up your

Raspberry Pi

“Use a motion-sensing Raspberry Pi

to automatically take pictures”

6 Raspberry Pi Tips, Tricks & Hacks

08 Master Raspberry

Pi in 7 days

• Make music with the

Raspberry Pi

• Raspberry Pi voice synthesiser

• Program Minecraft-Pi

• Get interactive with Scratch

• Build a Raspberry Pi web server

40 50 ways to master

Raspberry Pi

48 Use an Android device as a

Pi screen

52 Host a website on your Pi

54 Secure your Raspberry Pi

58 Build a file server with the

Raspberry Pi

62 Network and share your

keyboard and mouse

64 Add a reset switch to your

Raspberry Pi

66 Remotely control your

Raspberry Pi

68 Install Android on Pi

76 Add a battery pack to Pi

• Create your first simple game

with Scratch

• Learn to code with Sonic Pi

• Take photos with Raspberry Pi

• Use the GPIO pins

• Build a Twitter-powered lamp

with Python

• Make a tweeting bird watcher

Tips

2 8 5 Practical

Raspberry Pi

Projects

Tricks

• Retro arcade cabinet

• Audiobook reader

• Web radio

• Media caster

• Portable Wi-Fi signal repeater

• Secure Tor web station

• Private cloud storage

• AirPi

• Dusklights

• Outdoor time-lapse camera

96 Set up the PiTFT touch screen

98 Calibrate a touch screen interface

100 Portable Pi video player

102 Make a Raspberry Pi sampler

106 Build a radio transmitter

110 Tether your Pi to Android

112 Build a network of Raspberry Pis

116 Add gesture control to your Pi

120 Make a digital photo frame out of

your Raspberry Pi

124 Pygame Zero

132 Build a Raspberry

Pi-controlled car

138 Make a Raspberry Pi

car computer

146 Build a Minecraft power

move glove

150 Build a Super Raspberry Pi

Hacks

“It has powered quadcopters, coffee

makers, self-sailing boats and even

touched the edge of space”

80 10 Inspiring

Pi Projects

120

106

Master

Raspberry Pi

in 7 days

It’s amazing what can be accomplished with the

Raspberry Pi if you set your mind to it. They’ve been

sent higher into orbit than Felix Baumgartner, they

power cutting-edge Bitcoin farms and someone’s even

using one to try and translate dog thoughts into speech

with a Pi-infused collar. No prizes for guessing where

the inspiration for www.nomorewoof.com came from.

No one really knows if it’s ever going to work, but does

it matter? The mere fact that someone’s even trying to

bring a piece of Disney fantasy to life using the same

technology as your Raspberry Pi is inspiring stuff!

While we won’t be taking pictures at four times the

altitude of a cruising jumbo jet or translating the musings

of a canine companion, the seven projects you’ll ﬁ nd over

the next 16 pages will certainly get you off on the right

From setup to internet

sensation in a week…

foot. Our ﬁ nal big project will be to use a motion-sensing

Raspberry Pi to automatically take pictures of local

wildlife and tweet them to the world.

Not bad, especially since we’re assuming you have no

prior experience with the Raspberry Pi. Yes, we expect

you to know where to stick the other end of the HDMI

cable, but we don’t assume that you can program with

Python or navigate the command line interface. We’ll

gradually learn as we go, ﬁ rst by setting up the Pi and

learning key programming logic with Scratch and Sonic

Pi. We’ll then move on to writing simple Python scripts,

getting to grips with the Camera module and using the

GPIO port among other things. By the end of it you should

have all the skills and equipment needed to complete the

ﬁ nal project – and much more besides…

8 Raspberry Pi Tips, Tricks & Hacks

Master Raspberry Pi in 7 days

Raspberry Pi Tips, Tricks & Hacks 9

Master Raspberry Pi in 7 days

10 Raspberry Pi Tips, Tricks & Hacks

Day 1 Set up your Raspberry Pi

Day 3 Learn code with Sonic Pi

Day 5 Get to grips with GPIO

Day 6 Use the Twitter API Day 7 Put it all together!

Day 2 Make a game from Scratch

Day 4 Take photos with your Pi

It’s not rocket science, but we’ll get you started

Write functional code while making beautiful music

Create a simple but elegant candlelight project

Create an Internet of Things Twitter lamp

Automagically share wildlife shots with this motion-

sensing, picture-taking, Twitter-posting project

Learn the basics of coding with graphical feedback

Use Python to take great snaps with your camera

Plan your week

Master Raspberry Pi in 7 days

Raspberry Pi Tips, Tricks & Hacks 11

Master Raspberry Pi in 7 days

Pi projects

shopping list

Grab these extra components before

taking part in our week of Raspberry Pi…

We’ll be covering a variety of different project types over the course of

these tutorials, so you may want to stock up on some components and

accessories to help you get through the week. This is just the tip of the

iceberg, though - each supplier offers plenty of kit for new projects…

Pibow case Electronics starter kit

Raspberry Pi camera board PIR sensor

A beautiful and functional case for your Raspberry Pi, with all the

necessary openings that will allow you to access the camera module

ribbon and the GPIO port on the board itself. The Pibows come in a

variety of different colours, and there’s even a special version for the

Model A, with even greater access to the technical ports. It can also

be modiﬁ ed with an extra platter to attach to a TV if you plan on using

the Pi in your home theatre setup.

£12.95 | shop.pimoroni.com

Hobbyists have been creating simple circuits for their projects for

years now using simple components all hooked up to a prototyping

breadboard. While you can hunt around and get all the parts you

need for this, there are a handful of electronic starter kits that include

everything you need for our projects this issue (and much more besides).

Simon Monk has created one of these kits, which includes a breadboard,

pre-cut cables, switches, resistors and a whole host of other little

components and sensors for any electronics project.

£15 | bit.ly/1oE9BYC

The Pi-speciﬁ c camera board has been created in such a way that it

connects to one of the video in ports for the Raspberry Pi on the actual

board itself. This means it won’t use up any of the limited USB ports or

other inputs, so that you don’t need to get a USB hub to have everything

working. The camera isn’t the highest resolution offering in the world, but

it’s a respectable 5MP that can take images at 2592 x 1944 and record

video at 1080p at 30 fps, which is more than enough for most projects.

£19.99 | thepihut.com

An infrared motion sensor that hooks up to the Raspberry Pi via the

GPIO port. It sends a constant signal depending on the level of infrared

radiation that it detects, which can be used to determine when to activate

a piece of code. For example, IR sensors are classically used in alarm

systems, however they can also be used to take pictures or video on

demand, which is how we’re planning to use it at the end of the week.

£2.99 | modmypi.com

12 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

Set up your Raspberry Pi

Turn your Raspberry Pi into a fully functional PC

and get to know the basics of setting it up

What you’ll need

Q 1A micro USB

Q Internet connection

Q USB mouse and keyboard

Q HDMI cable and

compatible monitor

Q 4GB SD card

So you’ve just got your Raspberry Pi – you’re probably

wondering how exactly you’re going to get started with it.

If you’re used to more traditional PCs, you might be expecting

a CD drive or a USB installer to set up your Raspberry Pi. The

Pi requires a little more than sticking in a CD though, so we’ll

show you how to get everything working properly.

In this tutorial we’ll also give you some quick tips on how to

improve your Raspberry Pi experience, including extra software

packages and ways you can use your brand new Pi.

01 Get your operating system

Head over to the Raspberry Pi

website (www.raspberrypi.org) and

download NOOBS, the New Out Of Box

Software. This will come in a zip ﬁ le;

download it onto the SD card for your

Raspberry Pi and extract the ﬁ les from

it here. Do not extract the ﬁ les elsewhere

and copy them over.

Master Raspberry Pi in 7 days

Raspberry Pi Tips, Tricks & Hacks 13

The other distros each have

their uses and you may want to

use them at a later date

04 Install Raspbian

Select Raspbian by clicking the check box to the left

of it, and then click Install at the top of the Window. Conﬁ rm

that you want to install, and it will go through the process of

adding Raspbian to the SD card.

02 Connect your Pi

Without inserting the power cable, hook up everything to

your Pi. You’ll need a wired ethernet connection or a compatible

wireless dongle, a USB mouse, a USB keyboard and a monitor or

other form of display connected via HDMI.

05 Set up Raspbian

There are a few things you

need to do before Raspbian is ready.

On the conﬁ g screen, select Expand

Filesystem to make sure the SD is

being used properly. Then, go to Enable

Boot to Desktop and select Desktop

from the list. Go to Finish, and it will

reboot Raspbian.

03 Choose your distro

Plug in your SD card and ﬁ nally connect the power.

The Raspberry Pi will boot into NOOBS’ distro selection menu.

For all of our tutorials we will be using Raspbian, however

the other distros each have their uses and you may want to

consider using them at a later date.

06 Update Raspbian

Make sure all the software on

Raspbian is now up to date. To do this,

open the LXTerminal and type:

$ sudo apt-get update

Once that’s ﬁ nished, follow it up with:

$ sudo apt-get upgrade

This may end up taking a few minutes,

but it will update the software

throughout Raspbian.

07 Get new software

There are two ways to get more

packages for Raspbian – either through

the Pi Store link, or via the package

manager in the terminal. You’ll get a

different selection of apps on the two

services, with a greater focus on general

software tools in the package manager

08 Get an ofﬁ ce suite

Raspbian does not have any

form of ofﬁ ce functionality by default,

only a basic text editor. You can add

LibreOfﬁ ce though, which can be done

via the Pi Store. Open up the Store and go

to Apps; here you’ll ﬁ nd LibreOfﬁ ce as a

free download. Once you’ve created an

account, it will download and install it.

09 Get a better browser

Midori is an excellent browser,

however you can also get Chromium

to work on Raspbian. This is the open

source version of Google’s Chrome

browser, which you can get by opening

the terminal and typing:

$ sudo apt-get install chromium

Master Raspberry Pi in 7 days

14 Raspberry Pi Tips, Tricks & Hacks

Create a simple

game with Scratch

Learn the basics of coding logic by creating a squash-like

Pong clone in Scratch that you can play at the end of the day

While Scratch may seem like a very simplistic programming

language that’s just for kids, you’d be wrong to overlook it as

an excellent first step into coding for all age levels. One aspect

of learning to code is understanding the underlying logic that

makes up all programs; comparing two systems, learning to work

with loops and general decision-making within the code.

Scratch strips away the actual code bit and leaves you with

just the logic to deal with. This makes it a great starting point

for beginners, separating the terminology so you can learn that

later on when you choose to make a proper program. It’s also

included on every copy of Raspbian.

01 The ﬁ rst sprite

Opening up Scratch will display

a blank game with the Scratch cat;

right-click on it and delete to remove it.

Click the Paint New Sprite button

below the game window and draw a

slim rectangle as the bat using the

square drawing tool. Click Set Costume

Center so that Scratch knows the basic

dimensions of your bat; drag it to the

centre of the sprite if needs be.

Master Raspberry Pi in 7 days

Raspberry Pi Tips, Tricks & Hacks 15

04 Create the ball

Create a sphere from the new

sprite menu like we did with the bat,

including setting the Costume Center.

Name it ball, and bring the When Green

Flag Clicked block from the Control

menu into the scripts pane. Add the go

to x:0 y:0 block underneath it so that

whenever you click the green ﬂ ag it

resets to the ball.

02 Move the bat

Click OK, and name the new

sprite ‘Bat’. Select the Control block

from the top-left menu, and drag the

When Space Key Pressed block into

the script area. Change Space to Up

arrow from the drop-down menu, then

select the Motion options and drag the

Change Y By 10 block to connect to the

key pressed block.

05 Move the ball

Find the Forever block in the

control menu, and attach it under our

existing block on Ball. Then, go back

to the Motion menu and add Move 10

Steps so that the ball moves around

the screen. Add the If On Edge, Bounce

block from Motion below that so that it

will stay within the playing ﬁ eld.

03 Reverse the direction

Whenever we press up, the bat

will move up by ten pixels, as set. By

repeating the process using the down

arrow and setting Change Y To -10, we

can also make it move down as well.

Move the rectangle to the left side of the

screen. This will be our starting position.

06 Hit the ball

Drag the If block from Control to

below If On Edge, and then add touching

from Sensing to the empty space on the

If block. From the drop-down menu,

select Bat so that it will interact with

our bat sprite. Add one of the Turn 15

degrees blocks from Motion to the If

block, and change it to 180.

07 Simple bouncing

Pressing the green ﬂ ag now, the ball will bounce

between the left and right edges of the screen, or off the bat

if it comes into contact with it. We can make it slightly more

interactive to make use of the moving bat, and more like Pong.

08 Random bouncing

Go the Operators menu and select the ﬁ rst value, blank

+ blank. Drag it to where we have 180 degrees in the turn block,

and add 180 to the ﬁ rst blank space. Place the Pick Random 1

to 10 block in the second space and change the values to -10

and 10 so that whenever the ball hits the bat, it bounces off at a

random angle between 170 and 190 degrees.

09 Further developments

While you now have a functional game of sorts, you

can also add in a second player to make it truly Pong-like, and

add a scoring system by having a number increase when the

ball hits one of the sides.

Preview Test your

code straight away to

make sure it does what

you expect it to do

Building blocks

Use blocks that represent

coding to build your game

or animation

Build project

Export to the Scratch

website to show off your

work to the world

Code logic

Slot the blocks together

in a straightforward

manner to create loops

and comparisons

Master Raspberry Pi in 7 days

16 Raspberry Pi Tips, Tricks & Hacks

Learn to code

with Sonic Pi

Take the next step in programming and create your own

melodies with Sonic Pi, the musical programming language

What you’ll need

Q Speakers or headphones

Q Sonic Pi

With Scratch we’ve learned how

to operate under the logic of

programming. The next step is to

then use that within a programming

language – the problem is that many

of the available languages can look a

little intimidating. This is where Sonic

Pi comes in, offering a very simple

language style that can ease you in to

the basics of working with code.

It’s quite straightforward to use as

well – Sonic Pi allows you to choose

from a small selection of instruments

and select a tone to play with it. These

can be turned into complex melodies

using loops and threads and even

some form of user input.

01 Install Raspbian

If you’ve installed the latest version of Raspbian, Sonic

Pi will be included by default. If you’re still using a slightly older

version, then you’ll need to install it via the repos. Do this with:

$ sudo apt-get install sonic-pi

Master Raspberry Pi in 7 days

Raspberry Pi Tips, Tricks & Hacks 17

Sonic Pi offers you a very

simple language style that

can ease you into the basics

of working with code

04 Set the beat

For any piece of music, you’ll probably want to set the

beat. We can start by putting:

with_tempo 200

At the start of our code. We can then test this out by creating a

string of midi notes using play_pattern.

02 Get started with Sonic Pi

Sonic Pi is located in the Education category in the

menus. Open it up and you’ll be presented with something

that looks like an IDE. The pane on the left allows you to enter

code, and then you can save and preview it as well. Any errors

are displayed separately from the output.

05 Advance your melody

We can start making more complex melodies by

using more of Sonic Pi’s functions. You can change the note

type by using with_synth, reverse a pattern, and even create

a ﬁ nite loop with the x.times function. ‘Do’ and ‘end’ signify

the start and end of the loop.

03 Your ﬁ rst note

Our ﬁ rst thing to try out with Sonic Pi is simply being

able to play a note. Sonic Pi has a few defaults already pre-set,

so we can get started with:

play 50

Press run and the output window should show you exactly

what is happening.

06 Play a concert

Using the in_thread function, we can create another

thread for the Sonic Pi instance and have several lines of

musical code play at once instead of in sequence. Here we’ve

made it create a series of notes in a random sequence.

with_tempo 200

play_pattern [40,25,45,25,25,50,50]

2.tim es do

with_synth “beep”

play_pattern [40,25,45,25,25,50,50]

play_pattern [40,25,45,25,25,50,50].reverse

end

play_pad “saws”, 3

in_thread do

with_synth “fm”

6.tim es do

if rand < 0.5

play 30

else

play 50

end

sleep 2

end

2.tim es do

play_synth “pretty_bell”

play_pattern [40,25,45,25,25,50,50]

play_pattern [40,25,45,25,25,50,50].reverse

end

Full code listing

Master Raspberry Pi in 7 days

Take photos with

Raspberry Pi

Use the Raspberry Pi camera module to

capture photos and video, so you have a

portable camera for any situation

What you’ll need

Q Raspberry Pi camera board

Q picamera

github.com/waveform80/picamera

As we mentioned earlier, the Raspberry Pi camera module

is an excellent addition to the Raspberry Pi. Not only does

it slot into one of the non-traditional ports on the board itself,

but it’s also easily programmable within Raspbian. This gives

it a few beneﬁ ts over a USB webcam by not taking up any

USB slots and being easier to control with code. It’s also tiny,

making it as portable as the Raspberry Pi itself.

By the end of today, you’ll be able to use the camera like a

pro to create time delays and speciﬁ c image formatting.

01 Plug in your camera

To attach the camera to the Raspberry Pi, locate the

connectors between the ethernet and HDMI port and gently lift

up the fastener. Insert the camera board ribbon, with the metal

connectors facing away from the ethernet port.

18 Raspberry Pi Tips, Tricks & Hacks

Master Raspberry Pi in 7 days

Raspberry Pi Tips, Tricks & Hacks 19

04 Record some video

To record a video, we use a

similar command, raspivid, like so:

$ raspivid -o video.h264

Just like with the image-capturing that

we did in the previous step, this will

display a preview of what the camera

is seeing. However, the video actually

records the ﬁ ve seconds that make up

the preview as well.

02 Enable the camera

First you’ll need to make sure

the camera modules are enabled.

To start the standard conﬁ guration

screen, open a terminal and type:

$ sudo raspi-config

Navigate down to Enable Camera,

press Enter, and then simply key over to

enable and conﬁ rm with another press

of Enter. Select Finish and then reboot.

05 Advanced Pi camera uses

If you want to be able to do a

little more with the camera, there’s

a simple Python wrapper currently

available called picamera. You’ll need

to install it ﬁ rst though, and you can

do so from the terminal, using the

following command:

$ sudo apt-get install python-

picamera

07 Test explained

Press Ctrl+D to exit the Python shell. We just used

code similar to the command line tools to take a simple

image called ‘pythontest.png’. The most important thing

we did after that was ‘camera.close’, to make sure that the

camera was turned off after use.

09 More code

The above works a lot better in a Python script –

the wait is only really required if you can’t manually stop the

recording. Picamera allows you to create time lapses, modify

the frame rate of recordings and much more. For more ways

to use it, check out issue 137 of Linux User & Developer (bit.

ly/11lxQ7n) or the docs on the picamera GitHub page.

08 Python video

To record video with picamera, you need to ﬁ rst set

the resolution and then set a recording time.

import picamera

camera = picamera.PiCamera()

camera.resolution = (640, 480)

camera.start_recording(‘firstvideo.h264’)

camera.wait_recording(60)

camera.stop_recording()

camera.close()

03 Take your ﬁ rst picture

Capturing pictures with the

Raspberry Pi Camera is straightforward,

all you have to do is enter:

$ raspistill -o image.png

This will show a ﬁ ve-second preview of

the input of the camera and then capture

the last frame of the video.

06 Python test

Let’s make sure that everything we’ve done still works.

Enter a Python shell by typing ‘python’ into the terminal, and

then type the following three lines:

import picamera

camera = picamera.PiCamera()

camera.capture(‘pythontest.png’)

camera.close()

Carefully insert the connector for

the camera board, making sure

it’s the right way round

Master Raspberry Pi in 7 days

20 Raspberry Pi Tips, Tricks & Hacks

Use the GPIO pins

Learn to use the GPIO pins to interact with the outside world

– this is where Raspberry Pi projects get really interesting…

What you’ll need

Q Small breadboard

Q Small LED (any colour)

Q 330ohm resistor

Q 2x male-to-female

prototyping cables

The General Purpose Input/Output pins

(GPIO) give you power to interact with

the real world using your Raspberry Pi.

This project will get you comfortable with

using the GPIO pins, which will form the

backbone of the ﬁ nal project.

Traditionally the ‘Hello World’ program

for electronics prototyping is simply

turning a light on and off. We’re going to

go one better than that here though, by

simulating candlelight.

To do this we’re going to use the

Random and Time modules from

Python’s standard library to continually

change the brightness of the light while

using the RPi-GPIO library to control the

LED with Pulse Width Modulation (PWM).

01 Prepare your circuit

Before we turn on our Raspberry Pi we’ll make all the

physical cable connections to it. This requires us to place a

male-to-female cable on the ﬁ rst ground pin on the GPIO port

and another male-to-female cable on the PWM pin (pin 18).

Connect it to the breadboard along with the LED and resistor as

shown, ensuring the short leg of the LED goes to ground.

02 Power up the Pi

With the circuit complete we can power up the Pi.

Open Leafpad and we’ll start creating the script (found to the

right) we need to control the LED light. The ﬁ rst thing we do is

import the modules we need. The RPi.GPIO library is key to our

project – we use it to read and write to pins and control their

functionality. We’re also using Random and Time modules in

order to help simulate the effect of candlelight.

03 Conﬁ gure the GPIO module

Next we assign a name to the

LED pin and set up the GPIO module

for our project. Notice we’re using

‘setmode’ and calling it BCM. This

means we’re using the Broadcom

naming scheme. We then assign the

LED pin to OUTPUT, which means we’ll

be outputting to that pin (as opposed

to reading from it). If we simply wanted

to turn the light on and off, at this point

we could use GPIO.output(led,GPIO.

HIGH) and GPIO.output(led,GPIO.LOW).

Instead we’re using PWM, so we assign

a variable PWM to control it.

04 Basic functions

Next we create two very basic

functions that we can call in our main

program loop to randomly control the

physical brightness of the LED and the

amount of time that the light pauses

on a set brightness. To do this we ﬁ rst

use the random.randint method. The

numbers 5 and 100 represent the lowest

and highest brightness (in per cent) –

the function will then pick a number

between these percentages during each

Master Raspberry Pi in 7 days

Raspberry Pi Tips, Tricks & Hacks 21

The General Purpose Input/

Output pins give you the power

to interact with the real world

using your Raspberry Pi

loop through the program. random.random picks a ﬂ oating

point number between 0 and 1 – we divide this by WIND to help

achieve our ﬂ icker effect.

05 The main loop

Finally, we use a while loop to activate the light

with PWM and then change the brightness of the light

with the ChangeDutyCycle method, which calls our brightness

function. We do similar with time.sleep next to get the

brightness to maintain for a short, random, amount of time

by calling the ﬂ icker function. When we want to quit this

otherwise inﬁ nite loop, we can raise a KeyboardInterrupt

by pressing Ctrl+C. When we do, we need to free up the pins

so that they can be used again, by calling pwm.stop and

GPIO.cleanup respectively.

06 Test your project

Once your script has been written, save it as candle_

light.py. The ‘.py’ informs your Pi that this is a Python script.

To run it, simply open the Terminal and type the following:

sudo python candle_light.py

You need to call sudo here since you need to have admin

privileges to access the GPIO port on your Raspberry Pi.

Assuming you’ve set up the breadboard and copied the script

correctly, your LED light should start ﬂ ickering as if it’s a

candle in a light breeze. Take some time to experiment with

the variables in the brightness and ﬂ icker functions to achieve

a more desirable effect.

#!/usr/bin/env python

# Import the modules used in the script

import random, time

import RPi.GPIO as GPIO

# Assign the hardware PWM pin and name it

led = 18

# Configure the GPIO to BCM and set it to output mode

GPIO.setmode(GPIO.BCM)

GPIO.setup(led, GPIO.OUT)

# Set PWM and create some constants we'll be using

pwm = GPIO.PWM(led, 100)

RUNNING = Tr u e

WIND = 9

def brightness():

"""Function to randomly set the brightness of

the LED between 5 per cent and 100 per cent power"""

return random.randint(5, 100)

def flicker():

"""Function to randomly set the regularity of the'flicker

effect'"""

return random.random() / WIND

print "Candle Light. Press CTRL + C to quit"

# The main program loop follows.

# Use 'try', 'except' and 'finally' to ensure the program

# quits cleanly when CTRL+C is pressed to stop it.

try:

while RUNNING:

# Start PWM with the LED off

pwm.start(0)

# Randomly change the brightness of the LED

pwm.ChangeDutyCycle(brightness())

# Randomly pause on a brightness to simulate flickering

time.sleep(flicker())

# If CTRL+C is pressed the main loop is broken

except KeyboardInterrupt:

running

= False

print "\nQuitting Candle Light"

# Actions under 'finally' will always be called, regardless of

# what stopped the program (be it an error or an interrupt)

finally:

# Stop and cleanup to finish cleanly so the pins

# are available to be used again

pwm.stop()

GPIO.cleanup()

Full code listing

Ground

Ground 15

3.3v 5v

25v

414

17 18

22 23

3.3v 24

925

11 8

Ground 7

This is the top! The top of

the image represents the end of the

GPIO pins nearest your SD card

Grounded The pins are

counted from left to right and top

to bottom. This is one of the few

Ground pins, which we’ll be using

Special pins While most

pins can be manually set to be

outputs or inputs for any use, some

pins are pre-assigned other roles

too. This is the PWM pin, capable of

controlling motors and LEDs with

amazing precision

BCM for Broadcom

We’re using the BCM pin naming

scheme for our projects. It doesn’t

use the physical pin locations, so

BCM pin 17 is actually pin 11 when

counted from left to right

Master Raspberry Pi in 7 days

Build a Twitter-powered

lamp with Python

Now we know how to use the GPIO port, let’s see if we can

make our LED light work in response to the Twitter API…

What you’ll need

Q tweepy

Q Internet connection

Q Breadboard

Q Male-to-female cables

Q 300ohm resistor

Q LED

Over the last eight years Twitter has become one of the

most prominent social media networks in the world.

Twitter is built on excellent open source technology and code,

meaning it’s very easy to work with. With all the focus on the

tiny 140-character limit, you’d probably be surprised to hear

that behind each tweet is over 3,000 characters of raw data!

While we’re not going to harness the full power of Twitter’s

API today, we are going to do enough to allow us to make

a Twitter lamp – a light that ﬂ ashes whenever our chosen

phrase or word is mentioned on Twitter. It’s actually a lot

easier than you might think, so let’s get started…

01 Set up an app

Before you can do anything else,

you need to make sure that you’ve got a

Twitter account and that you’re signed

in. In order to be able to use the API, you

need to create a Twitter app, so head

over to https://apps.twitter.com and

click ‘Create New App’. Fill out the form,

but don’t worry about the URL sections

– just put any website for now, since we

won’t be using this functionality.

02 Configure the app

Once the app has been created

you can alter the access to Twitter by

modifying app permissions. While we

don’t need the ability to ‘write’ to Twitter

for this project, we will do in the next

one, so click ‘Modify App Permissions’

and change it to ‘Read and write’. Once

this changed, you can click the ‘Create

my access token’ button at the bottom

of the page. When this has refreshed,

you’ll have access to the info you need in

the ‘API Keys’ tab. Copy the API key along

with its secret and the access token and

its secret into a new document called

‘twitter_lamp.py’ in the format shown in

our code listing on the right.

22 Raspberry Pi Tips, Tricks & Hacks

Master Raspberry Pi in 7 days

Raspberry Pi Tips, Tricks & Hacks 23

It’s amazing what you

can achieve in just 50

lines of Python

04 Connect the LED

We’re going to use exactly the

same simple breadboard circuit we used

in the candlelight project on the previous

two pages – we’re even using the same

GPIO pins. With the circuit connected,

we can turn our attention to the code

listing on the right. The GPIO aspect

of the code is very similar to the last

project, other than the fact we’re using

the GPIO.HIGH and GPIO.LOW commands

to ﬂ ash the light, as opposed to PWM.

After our required imports at the top of

the code listing, we’ve laid out the api_key

and access_token phrases that point to

our Twitter app attached to our Twitter

account. Obviously we’ve masked over

ours, since they’re meant to be a secret.

Don’t share yours (even on GitHub)!

05 Using tweepy

After setting the keys and

secrets as variables, we need to get

tweepy to use them to authorise us.

Create the auth variable and use the

OAuthHandler to call them and then set

the access token details as shown.

03 Install tweepy

The next step in creating our

Twitter-powered lamp is installing and

setting up tweepy. In the terminal, type:

git clone https://tweepy/tweepy.git

Once it’s downloaded, move into the

directory (cd tweepy) and install it like so:

sudo python setup.py install

Once tweepy is installed we don’t need the

contents of the folder anymore. Go back to

your home folder (cd ~) and delete it with:

rm -rf tweepy

You can test that the library is installed

correctly by typing python in the terminal

to open the Python Interpreter. Now type

import tweepy – if you don’t get an error

when you hit Enter, you’re all set!

06 Test and tweak

Next we put our search terms into a list called terms.

As you can see, we’ve elected for our lamp to ﬂ ash whenever

one of the Raspberry Pi terms we’ve set is mentioned. You don’t

need to include ‘@’ or ‘#’ tags – the API takes care of that for us.

Now all that’s left to do is create an instance of the

StreamListener() class, start the Twitter live stream and then

use the ﬁ lter method to set it to only track the search terms

we’re interested in. It’s amazing what you can achieve in just

50 lines of Python! To test your new Twitter-powered lamp

prototype, at the terminal type:

sudo python twitter_lamp.py

We then use auth to allow us access to the Twitter API on our

account and test the connection by printing our Twitter handle

using the api.me() method. We want to use the real-time Twitter

stream for our project, though, so we need to override the

StreamListener class in tweepy to make our lamp work. The

on_status method in that class is where the magic happens;

whenever there’s a status update that’s relevant to us, it pings

on_status and we trigger our GPIO pins to make the light ﬂ ash.

#!/usr/bin/env python

#import the required libraries

import tweepy

import time

import RPi.GPIO as GPIO

# Set your access keys as configured

# at https://apps.twitter.com

api_key = 'your_api_key'

api_secret = 'your_api_secret'

access_token = 'your_access_token'

token_secret = 'your_token_secret'

# Initiate the OAuth process

auth = tweepy.OAuthHandler(api_key, api_secret)

auth.set_access_token(access_token, token_secret)

# Assuming the keys are good, you'll be

# able to test your Twitter app

api = tweepy.API(auth)

my = api.me()

print my.name, "is connected! Press CTRL + C to quit."

# Configure the GPIO port as we did in the last project

led = 18

GPIO.setmode(GPIO.BCM)

GPIO.setup(led, GPIO.OUT)

# Set the led light to be 'on'

GPIO.output(led, GPIO.HIGH)

# We've tweaked the class that monitors Twitter's stream

class StreamListener(tweepy.StreamListener):

# Whenever a status occurs that we're interested

# in we flash the LED

def on_status(self, data):

print "Flash the light"

# We're using a simple for loop that turns the light

# off and on three times using an interval of a

# quarter of a second

for i in xrange(3):

GPIO.output(led, GPIO.LOW)

time.sleep(0.25)

GPIO.output(led, GPIO.HIGH)

time.sleep(0.25)

def on_error(self, error_code):

print "Error:", error_code

return False

# These are the words we're looking out for on Twitter

terms = ['ra sp berr y pi', 'raspberrypi', 'ra spi']

# Configure the stream and filter only our chosen terms

try:

listener = StreamListener()

stream = tweepy.Stream(auth, listener)

stream.filter(track = terms)

except KeyboardInterrupt:

print "\nQuitting"

# Don't forget to clean up after so we

# can use the GPIO next time

finally:

GPIO.cleanup()

Full code listing

Master Raspberry Pi in 7 days

24 Raspberry Pi Tips, Tricks & Hacks

The tweeting bird watcher

Our ﬁ nal project! Create an Internet of Things device able to

takes pictures of wildlife before tweeting them to the web

What you’ll need

Q tweepy

Q Internet connection

Q HC-SR501 PIR Infrared

sensor

Q Camera board & picamera

library

We’ve reached the end of the week and

we’re now ready to take on our biggest

project yet. Our ﬁ nal project uses all of

the skills and technology we’ve covered

so far and raises the bar to include

things like automated Twitter updates

and event detection. We’re going to

create our own little Internet of Things

device that incorporates a simple PIR

sensor (just £2.99/$5 from modmypi.

com), the Raspberry Pi Camera board

and the power of the internet to let us

automagically capture images of birds

(and other wildlife) before tweeting to a

Twitter account of our choice whenever

activity occurs.

01 Conﬁ gure the

infrared sensor

Since this an automated device, we

need a way to trigger the camera when

movement is sensed in our camera’s

target area. One affordable and easy-

to-conﬁ gure solution is the HC-SR501

Infrared Motion Sensor. The device itself

has three pins – VCC (5V), Ground and a

signal pin that sits in the middle. We’ve

conﬁ gured our script for the pir pin to

trigger GPIO pin 17 (it sits opposite the

PWM pin). The VCC pin is connected

directly to the 5V power pin and the

Ground to the same Ground pin we’ve

used throughout the tutorials.

Master Raspberry Pi in 7 days

Raspberry Pi Tips, Tricks & Hacks 25

04 The callback function

One of the big changes in this project compared to

our previous ones is that we’re using the GPIO as an input,

instead of an output. Since we want the PIR sensor to alert

us to movement, we really want the PIR to interrupt our

script to let us know – that’s where our callback function

motion_sense() comes in. Looking further down the script to

the main program loop you’ll see a GPIO.add_event_detect.

Whenever the assigned GPIO pin gets pinged, the script will

stop what it is doing and jump to the named callback function

(in this case motion_sense). This simple function then calls the

take_picture function below it.

02 Test the PIR

We don’t want to send millions of accidental tweets to

Twitter, so we should do some pretty extensive testing with the

PIR ﬁ rst, using simple print statements to show when motion

has been detected. Visit github.com/russb78/tweety-pi and

explore the project to ﬁ nd the pir_testing.py script. Copy it

onto your Pi and run it with your PIR connected. You’ll probably

ﬁ nd that it’s over-sensitive for your needs by default. You’ll

ﬁ nd two tiny adjustable screws on the PIR. Gently adjust them

to the left to lower the sensitivity and test thoroughly until you

get the desired result.

05 Simple chain

The entire chain of main functions that make up

the meat of the project are laid out in trigger order and all

initiated from that initial callback function. Once motion

is detected the take_picture function is called. As soon

as the image has been saved to the /pics folder we call the

update_twitter function. Here, we’re loading our previously

saved image and using the Twitter API’s update_with_media

method to allow us to tweet our picture to the outside world.

We can set our status from within this line, but instead of

repeating the same phrase we use the random module’s

choice method to pick from a list of three we’d assigned to the

variable tweet_text earlier in the script.

03 Set up the project

With the camera connected as per our previous

camera project earlier in the week, we need to tie the camera,

motion sensor and Twitter code together to make a tangible

project that can be left to do its job. We’ll walk through the

script, but it’s worth looking around our project by cloning it

from GitHub. In the terminal type:

git clone https://github.com/russb78/tweety-pi.git

Enter the project with cd tweety-pi to take a look around.

It’s been set up as a full (if a little basic) project with a readme,

licence and even a folder for our pictures to sit in.

06 Main program loop

As we’ve done before, we’re placing our main program

loop in try, except, ﬁ nally blocks to ensure we can cleanly quit

the program or clean up should it crash for any reason. After

we call our GPIO event detect line, we create a simple inﬁ nite

loop to ensure the script keeps running. Pressing Ctrl+C will

break this loop, causing the program to end, but not before

ﬁ nally calling the methods that close the camera and shut-

off the GPIO pins. If you don’t do this, all kinds of issues can

arise the next time you run the script. And that’s all there is to

it! Be sure to use your knowledge on experimenting with other

Raspberry Pi projects – and have fun!

#!/usr/bin/env python

import RPi.GPIO as GPIO

import random, time, os

import tweepy

import picamera

pir = 17

GPIO.setmode(GPIO.BCM)

GPIO.setup(pir, GPIO.IN)

### TWITTER SETTINGS ###

# Set your access keys via https://apps.twitter.com

api_key = 'your_api_key_number'

api_secret = 'your_api_secret_number'

access_token = 'your_access_token_number'

token_secret = 'your_token_secret_number'

auth = tweepy.OAuthHandler(api_key, api_secret)

auth.set_access_token(access_token, token_secret)

api = tweepy.API(auth)

my_twitter = api.me()

print my_twitter.name, "is connected! Press CTRL + C to quit."

# Three statuses. We'll pick one at random to go with our pic

tweet_text = ['Another shot taken with tweety-pi!',

'Just spotted with my Raspberry Pi',

'Snapped automagically with my Raspberry Pi camera!']

### CAMERA SETTINGS ###

camera = PiCamera()

cam_res = (1024, 768)

camera.led = False # Turn off LED so we don't scare the birds!

pics_taken = 0

time.sleep(1)

### MAIN FUNCTIONS ###

def motion_sense(pir):

print "Motion detected... Taking picture!"

take_picture(cam_res)

def take_picture(resolution):

global pics_taken

camera.resolution = resolution

# Capture a sequence of frames

camera.capture(os.path.join(

'pics', 'im a ge_' + str(pics_taken) + '.j p g ' ))

pics_taken += 1

print "Picture taken! Tweeting it..."""

update_twitter()

def update_twitter():

api.update_with_media(os.path.join(

'pics', 'im a ge_' + str(pics_take n -1) + '.j p g ' ),

status = random.choice(tweet_text))

print "Status updated!"

#We don't want to tweet more than once per minute!

time.sleep(60)

### MAIN PROGRAM LOOP ###

try:

GPIO.add_event_detect(pir, GPIO.RISING, callback=motion_sense)

while True:

time.sleep(60)

except KeyboardInterrupt:

print "\nQuitting"

finally:

camera.close()

GPIO.cleanup()

Full code listing

Master Raspberry Pi in 7 days

Tips

64 Add a reset switch

62 Network and share your

keyboard and mouse

58 Build a file server with the

Raspberry Pi

54 Secure your Raspberry Pi

48 Use an Android device as a

Raspberry Pi screen

• Build a Raspberry Pi web server

• Get interactive with Scratch

• Program Minecraft-Pi

• Raspberry Pi voice synthesiser

• Make music with the Raspberry Pi

40 Why You Need Python 3

52 Host a website on your

Raspberry Pi 32

26 Raspberry Pi Tips, Tricks & Hacks

66 Remotely control Pi

28 5 Practical

Raspberry Pi Projects

76 Add a battery pack to

Raspberry Pi

68 Install Android

“This isn’t a random

selection. These are

practical ideas designed to

help kick-start bigger and

better things”

Raspberry Pi Tips, Tricks & Hacks 27

Tips | Tricks | Hacks

28 Raspberry Pi Tips, Tricks & Hacks

Still haven’t done anything with your Raspberry Pi?

Follow along with our expert advice and kick-start

your own amazing Raspberry Pi projects

5 PRACTICAL

RASPBERRY PI

PROJECTS

From our time experimenting with this incredible credit

card-sized computer, it’s become clear there are two types

of Raspberry Pi owners: those that use theirs and those

that don’t. Whether it’s fear of the unknown, a lack of time

or inspiration, when we ask people what they do with their

Pi we’ll often hear that it’s still in the box. If that’s you, then

you’re in the right place. In this feature we’ve handcrafted ten

Raspberry Pi projects practically anyone can enjoy.

These aren’t just a random selection of side-projects, though.

These are practical ideas designed to help kick-start bigger

and better things. Knowledge gained from one project can also

be applied to another to create something completely new.

For example, you could take what you’ll learn with the Sonic Pi

tutorial and go on to create a text-to-morse code translator.

You could go on to make Pong in Minecraft-Pi or use a button

attached to Scratch to take photos with your Raspberry Pi

camera module. The list goes on.

All these projects are open source, so you’re encouraged to

tweak and develop them into something entirely new. If you

share your tweaks and changes with the community, you’re sure

to start beneﬁ tting from doing things the open source way…

Raspberry Pi Tips, Tricks & Hacks 29

Tips | Tricks | Hacks

Program your own melodies using Sonic Pi and create

musical cues or robot beeps

What you’ll need

Q Portable speakers

Q Sonic Pi

www.cl.cam.ac.uk/projects/

raspberrypi/sonicpi/teaching.html

Make music with

the Raspberry Pi

One of the major features of Scratch is

its ability to teach the fundamentals

of coding to kids and people with no

computing background. For kids, its

especially appealing due to the way it

allows them to create videogames to

interact with as part of their learning. In

this kind of vein then, Sonic Pi teaches

people to code using music. With a

simple language that utilises basic logic

steps but in a more advanced way than

Scratch, it can either be used as a next

step for avid coders, or as a way to create

music for an Internet of Things or a robot.

01 Getting Sonic Pi

If you’ve installed the latest version of Raspbian, Sonic

Pi will be included by default. If you’re still using a slightly older

version, then you’ll need to install it via the repos. Do this with:

$ sudo apt-get install sonic-pi

QSonic Pi is a great way

to learn basic coding

principles and have fun

30 Raspberry Pi Tips, Tricks & Hacks

Raspberry Pi Tips, Tricks & Hacks 31

Tips | Tricks | Hacks

1 How to code

The coding

style of Sonic Pi

uses concepts

from standard

programming

languages – if

statements,

loops, threads etc.

Whereas Scratch

teaches this logic,

Sonic Pi teaches

their structure.

2 Robotic

voice

Employ Sonic Pi

to create context-

sensitive chips,

chirps and beeps

and use it to give a

familiar voice while it

tootles around.

3 MIDI

The Musical

Instrument Digital

Interface is a

standard for digital

music, and the

numbers and tones

used in Sonic Pi make

use of this.

You’ll

learn...

02 Starting with Sonic Pi

Sonic Pi is located in the Education category in the

menus. Open it up and you’ll be presented with something that

looks like an IDE. The pane on the left allows you to enter the code

for your project, with proper syntax highlighting for its own style

of language. When running, an info pane details exactly what’s

being played via Sonic Pi – and any errors are listed in their own

pane as well, for reference.

03 Your ﬁ rst note

Our ﬁ rst thing to try on Sonic Pi is simply being able

to play a note. Sonic Pi has a few defaults preset, so we can get

started with:

play 50

Press the Play button and the output window will show you what’s

being played. The pretty_bell sound is the default tone for Sonic

Pi’s output, and 50 determines the pitch and tone of the sound.

04 Set the beat

For any piece of music, you’ll want to set the tempo. We

can start by putting:

with_tempo 200

…at the start of our code. We can test it out by creating a string of

midi notes using play_pattern:

play_pattern [40,25,45,25,25,50,50]

This will play pretty_bell notes at these tones at the tempo we’ve

set. You can create longer and shorter strings, and also change

the way they play.

05 Advance your melody

We can start making more complex melodies by using

more of Sonic Pi’s functions. You can change the note type by

using with_synth, reverse a pattern, and even create a ﬁ nite loop

with the x.times function; do and end signify the start and end

of the loop. Everything is played in sequence before repeating,

much like an if or while loop in normal code.

06 Playing a concert

Using the in_thread function, we can create another

thread for the Sonic Pi instance and have several lines of musical

code play at once instead of in sequence. We’ve made it create

a series of notes in a random sequence, and have them play

alongside extra notes created by the position and velocity of the

mouse using the play_pad function.

with_tempo 200

play_pattern [40,25,45,25,25,50,50]

2.times do

with_synth “beep”

play_pattern [40,25,45,25,25,50,50]

play_pattern [40,25,45,25,25,50,50].reverse

end

play_pad “saws”, 3

in_thread do

with_synth “fm”

6.tim es do

if rand < 0.5

play 30

else

play 50

end

sleep 2

end

2.times do

play_synth “pretty_bell”

play_pattern [40,25,45,25,25,50,50]

play_pattern [40,25,45,25,25,50,50].reverse

end

Full code listing

“We can start making more

complex melodies by using

more of Sonic Pi’s functions”

Tips | Tricks | Hacks

32 Raspberry Pi Tips, Tricks & Hacks

Add the power of speech to your Raspberry Pi

projects with the versatile eSpeak Python library

QIt’s easier to make your Raspberry Pi talk

than you might think, thanks to eSpeak

Raspberry Pi

voice synthesiser

We’ve already mentioned how the

Raspberry Pi can be used to power

robots, and as a tiny computer it

can also be the centre of an Internet

of Things in your house or ofﬁ ce.

For these reasons and more, using

the Raspberry Pi for text-to-voice

commands could be just what you’re

looking for. Due to the Debian base

of Raspbian, the powerful eSpeak

library is easily available for anyone

looking to make use of it. There’s also a

module that allows you to use eSpeak

in Python, going beyond the standard

command-line prompts so you can

perform automation tasks.

01 Everything you’ll need

We’ll install everything we plan to use in this tutorial at

once. This includes the eSpeak library and the Python modules

we need to show it off. Open the terminal and install with:

$ sudo apt-get install espeak python-espeak python-tk

What you’ll need

Q Portable USB speakers

Q python-espeak module

QeSpeak

QRaspbian (latest image)

Raspberry Pi Tips, Tricks & Hacks 33

Tips | Tricks | Hacks

from espeak import espeak

from Tkinter import *

from datetime import datetime

def hello_world():

espeak.synth(“Hello World”)

def time_now():

t = datetime.now().strftime(“%k %M”)

espeak.synth(“The time is %s”%t)

def read_text():

text_to_read = input_text.get()

espeak.synth(text_to_read)

root = Tk()

root.title(“Voice box”)

input_text = StringVar()

box = Frame(root, height = 200, width = 500)

box.pack_propagate(0)

box.pack(padx = 5, pady = 5)

Label(box, text=”Enter text”).p a c k()

entry_text = Entry(box, exportselection = 0, 

textvariable = input_text)

entry_text.pack()

entry_ready = Button(box, text = “Read this”, 

command = read_text)

entry_ready.pack()

hello_button = Button(box, text = “Hello World”, 

command = hello_world)

hello_button.pack()

time_button = Button(box, text = “What’s the 

time?”, command = time_now)

time_button.pack()

root.mainloop()

Full code listing

02 Pi’s ﬁ rst words

The eSpeak library is pretty simple to use – to get it to

just say something, type in the terminal:

$ espeak “[message]”

This will use the library’s defaults to read whatever is written in

the message, with decent clarity.

03 Say some more

You can change the way eSpeak will read text with a

number of different options, such as gender, read speed and

even the way it pronounces syllables. For example, writing the

command like so:

$ espeak -ven+f3 -k5 -s150 “[message]”

…will turn the voice female, emphasise capital letters and make

the reading slower.

04 Taking command with Python

The most basic way to use eSpeak in Python is to use

subprocess to directly call a command-line function. Import

subprocess in a Python script, then use:

subprocess.call([“espeak”, “[options 1]”, “[option 

2]”,...”[option n]”, “[message]”)

The message can be taken from a variable.

06 A voice synthesiser

Using the code listing, we’re creating a simple interface

with Tkinter with some predetermined voice buttons and a

custom entry method. We’re showing how the eSpeak module

can be manipulated to change its output. This can be used for

reading tweets or automated messages. Have fun!

05 The native tongue

The Python eSpeak module is quite simple to use to just

convert some text to speech. Try this sample code:

from espeak import espeak

espeak.synth(“[message]”)

You can then incorporate this into Python, like you would any

other module, for automation.

Import the

necessary eSspeak

and GUI modules, as

well as the module

to ﬁ nd out the time

Deﬁ ne the different

functions that the

interface will use,

including a simple

ﬁ xed message,

telling the time, and

a custom message

Create the basic

window with Tkinter

for your interface,

as well as creating

the variable for

text entry

The text entry

appends to the

variable we

created, and each

button calls a

speciﬁ c function

that we deﬁ ned

above in the code

“You can change the way eSpeak

will read text with a number of

different options”

Get

the code:

bit.ly/

14XbLOC

Tips | Tricks | Hacks

Learn to program while playing one of the

greatest games ever made!

Program

Minecraft-Pi

Minecraft

is probably the biggest game

on the planet right now. It’s available on

just about any format you can imagine,

from PCs to gaming consoles to mobile

phones. It should probably come as

no surprise that it’s also available on

the Raspberry Pi. While at ﬁ rst glance

Minecraft-Pi is a simpliﬁ ed version of the

Pocket Edition (designed for tablets and

smartphones), the Raspberry Pi edition

is very special, in that it’s the only version

Minecraft

to gives users access to its

API (application programming interface).

In this project we’re going to show you

how to set up Minecraft-Pi and conﬁ gure

it so you can interact with

Minecraft

in a

way you’ve never done before. This small

project is just the tip of the iceberg…

01 Requirements

Minecraft-Pi requires you to be running Raspbian on

your Raspberry Pi, so if you’re not already running that, take a

trip to raspberrypi.org and get it setup. It also requires you have

X Window loaded too. Assuming you’re at the command prompt,

you just need to type startx to reach the desktop.

What you’ll need

Q Raspbian (latest release)

Q Minecraft-Pi tarball

Q Keyboard & mouse

Q Internet connection

QUnlike all

other versions of

Minecraft

, the Pi

version encourages

you to hack it

Raspberry Pi Tips, Tricks & Hacks 35

Tips | Tricks | Hacks

02 Installation

Make sure you’re already in your

home folder and download the Minecraft-

Pi package with the following commands

in a terminal window:

cd ~

wget https://s3.amazonaws.com/

assets.minecraft.net/

pi/minecraft-pi-0.1.1.tar.gz

To use it we need to decompress it. Copy

the following into the terminal window:

tar -zxvf minecraft-pi-0.1.1.tar.gz

Now you can move into the newly

decompressed Minecraft-Pi directory

and try running the game for the ﬁ rst time:

cd mcpi

./minecraft-pi

03 Playing Minecraft-Pi

Have a look around the game.

If you’re not familiar with

Minecraft

, you

control movement with the mouse and

the WASD keys. Numbers 1-8 select items

in your quickbar, the space bar makes you

jump and Shift makes you walk slowly (so

you don’t fall off edges). ‘E’ will open your

inventory and double-tapping the space

bar will also toggle your ability to ﬂ y.

04 Conﬁ guring the Python API

To take control of

Minecraft

with

the Python API, you next need to copy the

Python API folder from within the /mcpi

folder to a new location. In the terminal,

type the following:

cp -r ~/mcpi/api/python/mcpi 

~/ minecraft

In this folder, we want to create a

‘boilerplate’ Python document that

connects the API to the game. Write the

following into the terminal:

cd ~/minecraft

nano minecraft.py

With nano open, copy the following and

then save and exit with Ctrl+X, pressing

Y (for yes), then Enter to return to the

command prompt:

from mcpi.minecraft import 

Minecraft

from mcpi import block

from mcpi.vec3 import Vec3

mc = Minecraft.create() 

mc.postToChat(“Minecraft API 

Connected”)

05 Testing your Python script

The short script you created

contains everything you need to get

started with hacking Minecraft-Pi in the

Python language. For it to work, you need

to have the game already running (and

be playing). To grab control of the mouse

06 Hide & Seek

As you can see from the code above, we’ve created a

game of Hide & Seek adapted from Martin O’Hanlon’s original

creation (which you can ﬁ nd on www.stuffaboutcode.com).

When you launch the script, you’ll be challenged to ﬁ nd a

hidden diamond in the fastest time possible. We’ve used it to

demonstrate some of the more accessible methods available in

the API. But there’s much more to it than this demonstrates. If

you’re up for another Minecraft-Pi tutorial, see: bit.ly/1v4DR2F.

# !/usr/bin/env python

from mcpi.minecraft import Minecraft

from mcpi import block

from mcpi.vec3 import Vec3

from time import sleep, time

import random, math

mc = Minecraft.create() # make a connection to the game

playerPos = mc.player.getPos()

# function to round players float position to integer position

def roundVec3(vec3):

return Vec3(int(vec3.x), int(vec3.y), int(vec3.z))

# function to quickly calc distance between points

def distanceBetweenPoints(point1, point2):

xd = point2.x - point1.x

yd = point2.y - point1.y

zd = point2.z - point1.z

return math.sqrt((xd*xd) + (yd*yd) + (zd*zd))

def random_block(): # create a block in a random position

randomBlockPos = roundVec3(playerPos)

randomBlockPos.x = random.randrange(randomBlockPos.x - 50, randomBlockPos.x + 50)

randomBlockPos.y = random.randrange(randomBlockPos.y - 5, randomBlockPos.y + 5)

randomBlockPos.z = random.randrange(randomBlockPos.z - 50, randomBlockPos.z + 50)

return randomBlockPos

def main(): # the main loop of hide & seek

global lastPlayerPos, playerPos

seeking = True

lastPlayerPos = playerPos

randomBlockPos = random_block()

mc.setBlock(randomBlockPos, block.DIAMOND_BLOCK)

mc.postToChat(“A diamond has been hidden somewhere nearby!”)

lastDistanceFromBlock = distanceBetweenPoints(randomBlockPos, lastPlayerPos)

timeStarted = time()

while seeking:

# Get players position

playerPos = mc.player.getPos()

# Has the player moved

if lastPlayerPos != playerPos:

distanceFromBlock = distanceBetweenPoints(randomBlockPos, playerPos)

if distanceFromBlock < 2:

#found it!

seeking = False

else:

if distanceFromBlock < lastDistanceFromBlock:

mc.postToChat(“Warmer “ + str(int(distanceFromBlock)) + “ blocks away”)

if distanceFromBlock > lastDistanceFromBlock:

mc.postToChat(“Colder “ + str(int(distanceFromBlock)) + “ blocks away”)

lastDistanceFromBlock = distanceFromBlock

sleep(2)

timeTaken = time() - timeStarted

mc.postToChat(“Well done - “ + str(int(timeTaken)) + “ seconds to find the diamond”)

if __name__ == “__main__”:

main()

while in-game, you can press Tab. Open a

fresh terminal window, navigate into your

minecraft folder and start the script with

the following commands:

cd ~/minecraft

python minecraft.py

You’ll see a message appear on screen to

let you know the API connected properly.

Now we know it works, let’s get coding!

Functional, &

fun coding

There’s nothing too

taxing about our

code. We’ve created

a couple of simple

functions (starting

with def) and used

if, else and while to

create the logic.

You’ll

learn...

Full code listing

Tips | Tricks | Hacks

36 Raspberry Pi Tips, Tricks & Hacks

Experiment with physical computing by using Scratch

to interact with buttons and lights on your Pi

Get interactive

with Scratch

Scratch is a very simple visual

programming language, commonly

used to teach basic programming

concepts to learners of any age. In

this project we’ll learn how to light up

an LED when a button is pressed in

Scratch, and then change a character’s

colour when a physical button is

pressed. With these techniques

you can make all manner of fun and

engaging projects, from musical

keyboards to controllers for your

Scratch games and animations.

01 Installing the required software

Log into the Raspbian system with the username Pi and

the password raspberry. Start the LXDE desktop environment

using the command startx. Then open LXTerminal and type the

following commands:

wget http://liamfraser.co.uk/lud/install_scratchgpio3.sh

chmod +x install_scratchgpio3.sh

sudo bash install_scratchgpio3.sh

This will create a special version of Scratch on your desktop

called ScratchGPIO3. This is a normal version of Scratch

with a Python script that handles communications between

Scratch and the GPIO. ScratchGPIO was created by simplesi

(cymplecy.wordpress.com).

What you’ll need

Q Breadboard

Q LEDs

Q Buttons

Q Resistors

Q Jumper wires

Q ScratchGPIO3

QScratch can be used to do Internet Of

Things projects with a few tweaks

Raspberry Pi Tips, Tricks & Hacks 37

Tips | Tricks | Hacks

1 Simple

circuits

While these are very

simple circuits, you’ll

get a great feel of

how the Raspberry

Pi interfaces with

basic prototyping

kit. If you need to buy

the bits and pieces,

we recommend you

check out:

shop.pimoroni.com

2 Coding

principles

If you’re new to

programming,

Scratch is the

perfect place to

learn the same

programming

principles employed

by all programming

languages out there.

3 Physical

computing

There’s nothing more

magical than taking

code from your

computer screen

and turning it into a

real-life effect. Your

ﬁ rst project might

just turn a light on

and off, but with that

skill banked, the sky

is the limit.

You’ll

learn...

02 Connecting the breadboard

Power off your Pi and disconnect the power cable. Get

your breadboard, an LED, a 330-ohm resistor and two GPIO

cables ready. You’ll want to connect the 3.3V pin (top-right pin,

closest to the SD card) to one end of the 330-ohm resistor, and

then connect the positive terminal of the LED (the longer leg is

positive) to the other end. The resistor is used to limit the amount

of current that can ﬂ ow to the LED.

Then put the negative terminal of the LED into the negative

rail of the breadboard. Connect one of the GROUND pins (for

example, the third pin from the right on the bottom row of pins)

to the negative lane. Now connect the power to your Pi. The LED

should light up. If it doesn’t, then it’s likely that you’ve got it the

wrong way round, so disconnect the power, swap the legs around

and then try again.

03 Switching the LED on and off

At the moment, the LED is connected to a pin that

constantly provides 3.3V. This isn’t very useful if we want to be able

to turn it on and off, so let’s connect it to GPIO 17, which we can turn

on and off. GPIO 17 is the sixth pin from the right, on the top row of

pins. Power the Pi back on. We can turn the LED on by exporting

the GPIO pin, setting it to an output pin and then setting its value

to 1. Setting the value to 0 turns the LED back off:

echo 17 > /sys/class/gpio/export

echo out > /sys/class/gpio/gpio17/direction

echo 1 > /sys/class/gpio/gpio17/value

echo 0 > /sys/class/gpio/gpio17/value

uses pin numbers rather than GPIO numbers to identify pins.

The top-right pin (the 3.3V we first connected our LED to) is pin

number 1, the pin underneath that is pin number 2, and so on.

04 Controlling the LED from Scratch

Start the LXDE desktop environment and open

ScratchGPIO3. Go to the control section and create a simple script

that broadcasts pin11on when Sprite1 is clicked. Then click the

sprite. The LED should light up. Then add to the script to wait 1

second and then broadcast pin11off. If you click the sprite again,

the LED will come on for a second and then go off. ScratchGPIO3

05 Wiring up our push button

Power off the Pi again. This circuit is a little bit more

complicated than the LED one we created previously. The first

thing we need to do is connect 3.3V (the top-right pin we used to

test our LED) to the positive rail of the breadboard. Then we need

to connect a 10Kohm resistor to the positive rail, and the other end

to an empty track on the breadboard. Then on the same track, add

a wire that has one end connected to GPIO 4. This is two pins to the

right of GPIO 17. Then, on the same track again, connect one pin of

the push button. Finally, connect the other pin of the push button

to ground by adding a wire that is connected to the same negative

rails that ground is connected to.

When the button is not pressed, GPIO 4 will be receiving 3.3V.

However, when the button is pressed, the circuit to ground will be

completed and GPIO 4 will be receiving 0V (and have a value of 0),

because there is much less resistance on the path to ground.

We can see this in action by watching the pin’s value and then

pressing the button to make it change:

echo 4 > /sys/class/gpio/export

echo in > /sys/class/gpio/gpio4/direction

watch -n 0.5 cat /sys/class/gpio/gpio4/value

06 Let there be light!

Boot up the Pi and start ScratchGPIO3 as before. Go

to the control section and add when green ﬂ ag clicked, then

attach a forever loop, and inside that an if else statement. Go

to the operators section and add an if [] = [] operator to the

if statement. Then go to the sensing section and add a value

sensor to the left side of the equality statement, and set the

value to pin7. On the right side of the equality statement, enter

0. Broadcast pin11on if the sensor value is 0, and broadcast

pin11off otherwise. Click the green ﬂ ag. If you push the button,

the LED will light up!

Tips | Tricks | Hacks

38 Raspberry Pi Tips, Tricks & Hacks

Use Google Coder to turn your Raspberry Pi into a

tiny, low-powered web server and web host

Build a Raspberry Pi

web server

We’re teaching you how to code in many

different ways on the Raspberry Pi this

issue, so it only seems ﬁ tting that we

look at the web too.

There’s a new way to use the web on

the Raspberry Pi as well: internet giant

Google has recently released Coder

speciﬁ cally for the tiny computer. It’s a

Raspbian-based image that turns your Pi

into a web server and web development

kit. Accessible easily over a local network

and with support for jQuery out of the

box, it’s an easy and great way to further

your web development skills.

01 Get Google Coder

Head to the Google Coder website, and download the

compressed version of the image. Unpack it wherever you wish,

and install it using dd, like any other Raspberry Pi image:

$ dd if=[path to]/raspi.img of=/dev/[path to SD

card] bs=1M

What you’ll need

Q Internet connectivity

Q Web browser

Q Google Coder

googlecreativelab.github.io/coder/

raspberrypi/sonicpi/teaching.html

QGoogle Coder is a brilliant way to

introduce yourself to web development

Raspberry Pi Tips, Tricks & Hacks 39

Tips | Tricks | Hacks

02 Plug in your Pi

For this tutorial, you’ll only need to connect a network

cable into the Pi. Pop in your newly written SD card, plug in the

power and wait a few moments. If you’ve got a display plugged in

anyway, you’ll notice a Raspbian startup sequence leading to the

command-line login screen.

03 Connect to Coder

Open up the browser on your main system, and go to

http://coder.local. You may have to manually accept the licence.

It will ask you to set up your password, and then you’ll be in and

ready to code.

04 Language of the web

Now it’s time to create your own app or website. Click

on the ‘+’ box next to the examples, give your app a name and

then click Create. You’ll be taken to the HTML section of the app.

Change the Hello World lines to:

<h1>This is a HTML header</h1>

<p>This is a new block of default text</p>

05 Styled to impress

Click on the CSS tab. This changes the look and style of

the webpage without having to make the changes each time in the

main code. You can change the background colour and font with:

body {

background-color: #000000;

color: #ffffff;

}

06 Querying your Java

The third tab allows you to edit the jQuery, making

the site more interactive. We can make it create a message on

click with:

$(document).click(function() {

alert(‘You clicked the website!’);

}

);

HTML

<h1>Welcome to the internet...</h1>

<p><a href=”http://www.linuxuser.co.uk”>Linux User &

Developer</p>

<p><a href=”http://www.reddit.com/”>Reddit</p>

<p><a href=”http://www.linuxfoundation.org/”>The 

Linux Foundation</p>

<p><a href=”http://www.fsf.org/”>Free Software 

Foundation</p>

Java

var d = new Date;

var hours = d.getHours();

var mins = d.getMinutes();

if (hours > 12) {

var hour = (hours - 12);

var ampm = “PM”;

}

else {

var hour = hours;

var ampm = “AM”;

}

if (hours == 12) {

var ampm = “PM”;

}

if (mins > 9){

var min = mins;

}

else {

var min = “0” + mins;

}

var time = “The time is “ + hour + “:” + min 

+ “ “ + ampm;

$(“h2”).h t m l(t i m e);

Full code listing

Some simple HTML

code that can

point us to some

important websites.

The h2 tag is used

to display the time

thanks to Java

We’re calling the

current time using

jQuery in the JS

tab so that we can

ultimately display it

on the webpage

We’re going to

display the time as a

12-hour clock in the

ﬁ rst if statement,

and use AM and PM

to differentiate

the time

We make the

minutes readable

by adding a 0 if

it’s below 10, then

concatenate all

the variables and

assign to the tag h2

Whether you’ve just got your lucky hands

on a powerful, petite Raspberry Pi Zero or

you’re looking to maximise the efﬁ ciency of

the faithful Raspberry Pi you already own,

this is everything you need to get started

on boosting not only your Raspberry Pi but

your own knowledge. The Raspberry Pi is

a versatile little piece of hardware, with a

wonderfully creative amount of potential, and

though most of you will be familiar with its

more day-to-day functions, there are always

tweaks and adjustments to be explored that

can tailor the Raspberry Pi to your own desired

user experience.

From soldering to useful Python features,

GPIO interrupts to remote access, and a whole

lot more, this masterclass in technical and

practical skills covers ﬁ fty useful ways to get

the most out of your Raspberry Pi. If you’re

anything like us, you’ll have been tinkering

around with your Raspberry Pi Zero, but

whatever your skill level there’s still something

here for you to get your teeth into.

Every single tip here will work on your Pi

Zero; just keep an eye out for the ‘Zero’ ﬂ ash,

indicating which are relevant to the Pi Zero

only. Those of you using an earlier model won’t

be missing out, though – how could we ever

neglect our favourite single-board computer?

– the majority of tips, tricks and tweaks are

still suitable for any other ofﬁ cial Raspberry Pi

as well. Have fun tinkering!

MASTER

RAS PI

WAYS TO

Get the most out of your

Pi with these expert tips and tricks

40 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

The newest member of the Raspberry Pi family, this tiny

board is the result of the Raspberry Pi Foundation’s efforts

to reduce the cost of the computer even further. Not content

with reducing its $35 computer to $25, which can still be a little

pricy for some people, it has cut it right down to $5 by making a

few adjustments. Here’s what you need to know.

03 Find your Pi on a network

If you can’t log into your router to view DHCP leases, you can use

nmap (available for Linux, Windows and Mac) to scan the local network

to ﬁ nd a Raspberry Pi. You need to know the address range of your local

network (common networks are 192.168.1.0/24, and 192.168.2.0/24).

nmap -sn 172.17.173.0/24 will run a ping scan and output a list of devices.

An example output is:

Nmap scan report for raspberrypi.home.org (172.17.173.21)

Host is up (0.0011s latency).

06 Enable max current draw

If you have a good power supply (ie

2 amps or more) and want to be able to

connect a current-heavy device to your Pi

2 or B+, such as a USB hard disk, then you

can add the line max_usb_current=1 to

/boot/config.txt, which will set the max

current over USB to 1.2 amps instead of the

default 600mA.

04 Experiencing stability issues?

By far the biggest cause of stability issues is the power supply

you are using, especially now the Raspberry Pi 2 has more CPU cores

and so uses more energy. The recommended current supply for a

Raspberry Pi 2 or B+ is 1.8 amps. If you are still having issues, your SD

card may be worn out.

05 Forgot to type sudo?

Sudo is used to get root privileges for a speciﬁ c command (for example,

editing a ﬁ le in /boot or /etc). The variable !! in bash is the previous command that

you typed. So if you need root privileges for something but forgot to type sudo

then you can simply type sudo !!, provided you haven’t typed anything else since.

Essential tricks to improve

day-to-day use

Vital knowledge

Micro-USB One of these ports

is for your micro-USB power

supply. To use peripherals and

a Wi-Fi dongle, you’ll need a

micro-USB to USB adaptor so

you can attach a powered

USB hub.

Pinless port The GPIO header is the same

as in the newer models but comes without the

pins. You’ll need to solder on a 40-pin male

header block.

Mini-HDMI You’ll

need a mini-HDMI to

HDMI cable to use your

monitor as a display.

You can use your TV with

the RCA video-out if you

solder the pin.

BCM2835 This is the same processor used

in the original Raspberry Pi models, although

it’s been overclocked to run at 900MHz and is

about 40% faster.

01 Raspberry Pi Zero

Ensure

you have the latest

packages on Raspbian

by running sudo apt-get

update; sudo apt-get

upgrade from a

terminal

Zero

07 Control options

sudo raspi-config can be

used to change several options.

For example, to enable the

camera, overclock the Pi, change

boot options, and expand the

filesystem to use the full space on

the SD card.

Tips | Tricks | Hacks

Handy hints and vital info to get the most out of

any Raspberry Pi model

Transferable tips

Raspberry Pi B+

08 Remote access with SSH

SSH stands for Secure Shell. You can use SSH to

connect to a terminal session on your Raspberry Pi over your

local network. This means that you can use the Pi with only a

network cable and power cable connected, which is much more

convenient than needing a screen and keyboard. Once you have

found your Pi on the network you can log into it using the default

username of ‘pi’ and the default password of ‘raspberry’. Both

Linux and Mac will have built-in SSH clients, so simply open the

terminal and type ssh pi@192.168.1.5, assuming that 192.168.1.5

is the address of your Pi. On Windows, you can use an SSH client

called PuTTY, which is free to download, doesn’t need installing

and is easy to ﬁ nd with a search engine.

09 Copy ﬁ les using SCP

SCP stands for Secure Copy Protocol, and is a way for

you to copy ﬁ les (and directories) to and from your Raspberry Pi

over the network. A good use of this would be if you have art for a

PyGame project and you need to copy it over. FileZilla is a decent

graphical SCP client to use (connect to your Pi on port 22 with the

username ‘pi’ and password ‘raspberry’). If you are using SCP

from the terminal then the syntax is as follows:

scp -r testdir/pi@172.17.173.21:~/

The -r switch is for recursive, which means entire directories

are copied in addition to ﬁ les. This will place your test directory

in /home/pi/ (because ~ points at the logged-in user’s home

directory on Linux). Simply swap the syntax for copying from the

Raspberry Pi instead:

scp -r pi@172.17.173.21:~/testdir .

The dot refers to the current directory in Linux, so the testdir

directory would be copied to the current directory.

10 USB controller The USB controller on

the Pi is theoretically capable of 480Mbit/s.

On earlier Pi models the performance is limited

by the single core ARM chip, but it is possible to

get close to that limit on a Pi 2.

12 SD cards SD cards aren’t really

designed for running an operating system.

Higher class SD cards don’t necessarily mean

better performance for lots of small ﬁ les. The

Raspberry Pi foundation recommend its SD

card, which is an 8GB class 6 microSD card.

13 Ethernet LEDs There are two LEDs

below the Ethernet port of a B+ onwards.

The orange light means there is a link, and the

ﬂ ashing green light means there is activity.

14 Wi-Fi module To get your

Pi online without an Ethernet

connection, you’ll need a Wi-Fi module.

We advise on an official one, but look for

802.11 b/g/n modules if going third-party.

11 Power / Act LEDs

The remaining LEDs

are for power and SD card

activity. The power LED is

red, and the activity LED

ﬂ ashes green when there is

SD card activity. The activity

LED also ﬂ ashes when

powering down to indicate

when it is safe to disconnect.

Above Get a terminal

on your Raspberry

Pi from the

convenience of your

main computer

42 Raspberry Pi Tips, Tricks & Hacks

Raspberry Pi Tips, Tricks & Hacks 43

Using an Ethernet adapter with your Pi Zero Navigate your way around

the command line with ease

Five terminal

tricks

15 Get your Pi Zero online

16 Set up a VNC server

VNC stands for Virtual Network Computing. Using

VNC, you can access the Raspbian desktop over the

network (meaning you only need power and Ethernet

connected). There is no audio support but for any other

tasks (including the use of Pygame), VNC should provide

acceptable performance. You can install a VNC server

with the following commands…

sudo apt-get update

sudo apt-get install tightvncserver

There are several free VNC clients available, so a search engine

will help ﬁ nd a suitable one. To start a VNC session on your Pi, log

in over SSH and then run tightvncserver. You will be prompted

to enter a password the ﬁ rst time you run it. You can specify

a screen resolution with the -geometry option, for example

-geometry 1024x768. You can kill an existing VNC session with

tightvncserver -kill :1, where 1 is the session number. To connect

to that session on a Linux machine, you could use the command:

vncviewer 172.17.173.21:1, substituting for the IP address of your

Raspberry Pi.

18 Listing open ports

Lsof stands for List Open Files, and you can install

it with sudo apt-get install lsof. If you run sudo lsof -i

you will see a list of all open network connections on the

machine, including applications that are listening for new

connections (for example, the SSH daemon).

19 Using wget to download ﬁ les

Wget can be used to download ﬁ les from the

Internet from the terminal. This is convenient if you need

to download a zip ﬁ le containing source code and then

extract it. For example:

wget http://liamfraser.co.uk/test.zip

unzip test.zip

20 Using htop to monitor load

Htop is an improvement on the original top utility.

It lets you see the CPU and memory load on your machine

in real time, which is useful to know how intensive your

application is being on a Raspberry Pi. You can install it

with sudo apt-get install htop.

21 Reboot from the terminal

It seems like a simple tip but not everyone knows

that you can reboot your Pi with the command sudo

reboot, and similarly power it off with sudo poweroff.

You need to disconnect and reconnect the power after

powering off the Pi, though, as there is no on/off switch.

22 Using screen

Screen (available via apt-get) is great if you have

something you want to run that takes a long time. You can

run it in a screen session, detach from it and reconnect

later on. Example usage:

screen -S test (Ctrl + A, d to disconnect)

screen -ls to list sessions.

screen -r test to reconnect

exit will kill bash and therefore end the screen session.

Step One: The parts

You’ll need an adapter to connect

the micro-USB port to a full size USB

port. This adapter, along with a mini-

HDMI to HDMI adapter and GPIO pin

headers can be found here: http://

swag.raspberrypi.org/products/pi-

zero-cables. You’ll also need a USB to

Ethernet adapter that works with Linux

(most will work out of the box), These

can easily be found on Amazon for

around £10.

Step Three: Testing it out

If the activity lights on your USB to

Ethernet adapter are lit, then it should

be working ﬁ ne. You can now use the

remote access tips from other sections

of the article with your Pi Zero!

Step Two: Conﬁ guration

As the Pi Zero uses the normal

Raspbian image, and eth0 (ie the built-

in Ethernet card) is missing, there is no

conﬁ guration necessary because the

USB Ethernet card will take the missing

LAN chip’s place as eth0.

Left Access the

Raspbian desktop

from your main

computer over your

local network

The sync

command ensures that

everything has been

ﬂ ushed to permanent

storage from the cache. It

can be useful to run after

updating packages,

for example.

Zero

23 split ﬁ les

If your program is large, you can split it up into

multiple ﬁ les. If you have a ﬁ le called MyClass.py

containing a class MyClass, you can use it from another

script with from MyClass import MyClass

Raspberry Pi Tips, Tricks & Hacks 43

Tips | Tricks | Hacks

You can use

negative indexes on

Python lists to get the

most recently added

item(s). mylist[-1] will get

the latest thing that

was added to

the list.

Here are some handy Python features that will make

your code really stand out

Become a Python Pro

24 The main function

Having a main function (if __name__ ==

__main__) in Python is useful. It makes it easier to

see the difference between where your functions/

classes are defined and where your entry point is.

More importantly, it allows you to only run code

from that Python script in the case that it is the

main script being run. This means that you can

create a class and have code that tests that class

to make sure it works. However, if you were to

include your file in another program, the code in

the main method would not be run and you can

just use the class that you require.

class MyClass:

def __init__(self):

self.x = 1

def print_increment(self):

print “x = {0}”.format(self.x)

self.x += 1

if __name__ == “__main__”:

# Test MyClass

m = MyClass()

m.print_increment()

25 Command line arguments

Command line arguments enable your

program to run in various modes depending on

the options that the user passes to the program

when running it. Command line arguments in

Python are given in sys.argv, which is a list of

arguments. The ﬁrst argument is always the

name of the script that has been executed. For

example, some code that prints the argv array

produces the following outputs:

$ python args.py

[‘a r g s.p y’]

$ python args.py --foo

[‘a rg s.py’, ‘-- fo o’]

You can check for command line arguments in

this list. If the length of the list is 1 and you require

arguments, print a help message with instructions.

import sys

help_msg = “My help message”

debug_mode = False

if __name__ == “__main__”:

if len(sys.argv) == 1:

print help_msg

sys.exit()

if “--debug” in sys.argv:

debug_mode = True

print “Using debug mode”

26 Using properties and setters

Properties in Python are a way to write

getters and setters for variables. You need new-

style classes (you need to inherit from object). We

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takes place in Belgium and has

grown wildly over the years

27 Python conferences 28

44 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 45

Uncover the secrets to be

found in Python

Five hidden

features

30 List comprehension

List comprehension is a way of generating a list on a

single line. You can use list comprehension to extract values

from other list-type data structures. For example, if you

have a collection of distance classes, you could get just the

distance in miles into a list: miles = [x.miles for x in

distances]. Here is a sample output:

>>> [x/2.0 for x in range(0, 10)]

[0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5]

31 Assertions

Assertions are useful when writing algorithms.

They are used to check the data is valid before and after

your algorithm. So, for example, if you are expecting your

results in a certain range you can check them. The syntax is

assert(boolean expression). For example:

>>> assert(0 < 1)

>>> assert(1 < 0)

Traceback (most recent call last):

File “<stdin>”, line 1, in <module>

AssertionError

32 Throwing exceptions

It’s useful to throw exceptions in your code if it’s

possible that it can go wrong. That way the person calling

your code can put it in a try-catch block and handle the

exception if it is raised. If the caller does not handle it then

their application will crash.

>>> raise ValueError(“Supplied value out of range”)

Traceback (most recent call last):

File “<stdin>”, line 1, in <module>

ValueError: Supplied value out of range

33 Running your script from a terminal

If you begin your Python script with #!/usr/bin/env

python and then mark it as executable, you can execute it

from bash just like a normal script without having to type

Python before it:

$ echo ‘#!/usr/bin/env python’ > test.py

$ echo ‘print “Hello World from Python!”’ >> test.py

$ chmod +x test.py

$ ./test.py

Hello World from Python!

34 Using the interpreter

Did you know you can start a Python interpreter to test

things are working without having to write a Python script?

Just type python into the terminal and then simply start

writing Python.

Above Not sure whether to pick Python 2 or 3? There’s a guide to help in the docs: bit.ly/1jyd799

have created a class called distance where

the distance in miles is a variable, and

the distance in kilometres is a property.

Getting from that variable multiplies the

distance in miles to be kilometres and

setting the variable sets the value in miles.

class Distance(object):

KM_PER_MILE = 1.60934

def __init__(self, mi):

self.miles = mi

@property

def km(self):

return self.miles * Distance.

KM_PER_MILE

@km.setter

def km(self, value):

self.miles = value / Distance.

KM_PER_MILE

if __name__ == “__main__”:

d = Distance(3.1)

print d.km

d.km = 10

print d.miles

print d.km

Get to grips with the GPIO library

29 Using the GPIO

Step One: Import library

Start by importing Rpi.GPIO:

import RPi.GPIO as GPIO

Then, you want to set the pin numbering

convention to the Broadcom mode (as

in GPIO17 will be pin 17, rather than

being pin 11 on the Pi):

GPIO.setmode(GPIO.BCM)

Step Three: Get values

Once the pins are set up, getting

values from them is easy. To get the

value of a pin (0 for low, and 1 for high),

use the following syntax:

value = GPIO.input(6)

…and to set the value of a pin (with

either 0 or 1, or True or False) use the

following syntax:

GPIO.output(5, True)

Please note that if you are starting

with Raspbian Jessie, you shouldn’t

need sudo to access the GPIO pins,

but in previous versions of Raspbian

you will need to use sudo to run

your code.

Step Two: Pin setup

Now you need to set up your pins

as either inputs or outputs with the

following syntax:

GPIO.setup(5, GPIO.OUT)

GPIO.setup(6, GPIO.IN)

If you have several pins to set up, it

makes sense to put them in a list and

then do something like:

for p in pins:

GPIO.setup(p, GPIO.OUT)

35 remove static

Make sure you haven’t built up any static charge when

working with electronics. Touching a grounded radiator in

your house can be a good way of getting rid of static charge.

Raspberry Pi Tips, Tricks & Hacks 45

Tips | Tricks | Hacks

40 Pin layout

0201

0403

0605

0807

1009

1211

1413

1615

1817

2019

2221

2423

2625

2827

3029

3231

3433

3635

3837

4039

3V3

Power

Ground

GPIO14

UART0_TXD

3V3

Power

GPIO23

Ground

GPIO8

SPIO_C E0_N

GPIO13

GPIO12

GPIO3

SCL1 I2C

Power

GPIO27

GPIO18

PCM_CLK

GPIO9

SPIO_MISO

Ground

GPIO5

ID_SC

I2C ID EEPROM

GPIO26

GPIO16

GPIO21

GPIO2

SDA1 I2C

Power

GPIO17

GPIO15

UART0_RXD

GPIO10

SPIO_MOSI

GPIO24

ID_SD

I2C ID EEPROM

GPIO7

SPIO_C E1_N

GPIO19

Ground

GPIO4

Ground

GPIO22

Ground

GPIO11

SPIO_SCLK

GPIO25

GPIO6

Ground

GPIO20

GPIO interrupts, pulse width modulation, soldering and more

Solder with ease in just a few steps

Hardware how-to

41 How to solder

Step One: The tools

You need a soldering iron (30-40 watts, or ideally

a temperature-controlled one), a stand to put it

in, a damp sponge to clean the tip, and some thin

solder. Lead solder is easier to work with than

lead-free, and an iron with a square tip conducts

heat better than a pointy one.

Step Three: If you make a mistake

You probably won’t need as much solder as you

think you will, so be sparing. Still, accidents can

happen, and the best way to remove excess solder

is to get some de-soldering braid. This is copper

that you put over solder, before putting the iron

over the top. The solder is sucked onto the braid.

Step Two: Soldering

Once the iron is hot, apply some solder to the tip

of the iron and wipe off any excess on the sponge.

When pressing the iron to the joint, the tip should

be touching both the joint and the wire you are

soldering. Do not apply solder directly to the iron;

apply it to the joint/wire.

37 Serial

console

If you connect the

UART0_TXD pin to

the receiver pin of

a USB-to-serial

converter, and the

UART0_RXD pin to

the transmitter pin

of that converter,

you can set up a

serial console.

GPIO explained

36 GPIO

orientation

The best way to

verify you have the Pi

oriented the right way

is to ﬂ ip it over. The

underneath of pin 1

has a square hole for

the solder instead of

a circular hole.

39 Soldering

headers

With the Pi Zero, you

will need to solder

GPIO headers onto

the board. Using a

reusable adhesive

like Blu-Tack to hold

the headers in place

will make the job

much easier.

38 Unused

GPIO pins

The green coloured

GPIO pins are unused

by default and

are therefore the

best pins to use in

your own personal

hardware projects.

The other pins may

have more than one

available purpose.

Zero

46 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 47

Quick and easy things you

can try in a few minutes

Five-minute

practical fixes

43 Pulse width modulation

Pulse width modulation is

where the output of a GPIO pin is high

for a percentage of time and low for

the remaining percentage of time. The

percentage where the pin is high is called

a duty cycle. Pulse width modulation

is very useful in electronics, especially

when it comes to tasks like controlling the

brightness of LEDs. To do this in Python:

GPIO.setup(5, GPIO.OUT)

# Frequency of 50 hz

p = GPIO.PWM(5, 50)

# 50 percent duty cycle

p.start(50)

# Do work or wait here so

# program doesn’t exit

# 70 percent duty cycle

p.ChangeDutyCycle(70)

p.stop()

44 GPIO interrupts

An interrupt is when a hardware

event triggers an interrupt on the CPU,

causing it to stop what it is dealing with

and run an interrupt request handler. The

Raspberry Pi can trigger inputs when a

GPIO pin goes high (ie from 0V to 3.3V) or

low (from 3.3V to 0V). This can be more

efﬁ cient than polling for the state of a

GPIO pin, as you only have to deal with the

pin changing when it happens. Plus, it can

actually simplify the ﬂ ow of your code.

The use of interrupts requires root

privileges so you will have to execute

your code with sudo. The code provided

demonstrates how to set up a callback

function to deal with a rising edge.

45 Using a push button

Refer to the circuit diagram

below. When the push button is

pressed, the left pins are connected

to the right pins. By using a 10K pull

down resistor connected to ground, the

purple output wire (connected to a GPIO

pin conﬁ gured as an input) defaults

to 0V when the button is not pressed.

The right-hand side of the button is

connected to 3.3V, so when the button

is pressed, the left-hand side of the

button will also be connected to 3.3V.

The left-hand side is connected in

parallel with the purple signal wire,

and also the 10K resistor to ground.

Because electricity takes the path of

least resistance, the purple signal wire

will output 3.3V.

46 Need more current?

You should only draw a few milliamps of current

from the GPIO pins of the Raspberry Pi. If you need more

current than that (or you need to switch a higher voltage),

then you can use the GPIO pin to switch a transistor

connected to a stronger voltage source.

47 Disable built-in sound card

If you are using a USB sound card then it can be

easier to disable the built-in sound card completely:

sudo rm /etc/modprobe.d/alsa*

sudo editor /etc/modules

Change snd-bcm2835 to #snd-bcm2835 and save, then

sudo reboot.

48 Use a multimeter to verify orientation

You can use a multimeter to verify the orientation

of the GPIO pins. Looking vertically, with the USB ports at

the bottom, the bottom-left pin (39) is ground and the top-

right pin (2) is 5V. Using the negative terminal on ground

and the positive terminal on 5V should show ~5V.

49 Set up serial console

You can use raspi-conﬁ g to set up a serial console so

you can get a login shell using the UART0_TX and UART0_RX

pins by connecting them to a USB to serial adapter:

sudo raspi-config

8 (Advanced Options)

A8 (Serial)

Select Yes to enable serial console. Finish, then reboot.

50 LED resistor calculations

To calculate an LED’s resistance value, use Ohm’s law:

Resistance = voltage / current. The voltage of a GPIO pin is

3.3V. You need to know the voltage drop of the LED and its

suggested current, so R = (3.3V – voltage_drop) / led_current.

Using 2V as the voltage drop and 20mA as the current: (3.3 –

2.0) / 0.02 = 65 ohms. Round up to the next available resistor.

Above Here are two waves with duty cycles of

roughly 80% (top) and 20% (bottom)

Above The blue wire is the ground, the red one

is 3.3V and purple is for the output

Ensure you are

only using 3.3V voltage

levels when working with

the GPIO pins. Connecting

anything higher than 3.3V

to a GPIO pin will likely

damage your Pi.

Raspberry Pi Tips, Tricks & Hacks 47

Tips

| Tricks | Hacks

48 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

What you’ll need

Q TightVNC tightvnc.com

Q VNC Viewer bit.ly/1jCzBRJ

Connect to a Pi with your phone or tablet

using VNC as a secondary or actual display

Use an Android device

as a Raspberry Pi screen

There are a few ways to attach a display to a Raspberry Pi.

The ones that everyone is most familiar with are the HDMI

port, which can go straight into your monitor or TV, or via

the GPIO ports with a portable screen. One avenue that is

rarely pursued is using VNC software to remotely view the

Raspberry Pi desktop using another computer entirely.

It’s actually fairly simple and we are going to concentrate on

viewing your Pi screen via Android for maximum portability.

With further tweaks you will be able to use this on the go if

you ﬁ nd yourself commuting and wanting to catch up on your

favourite program, for example.

There are a few things that you should be aware of when

doing this project – it can be quite taxing on the Pi and is

likely to drain a bit of battery from your phone too. We will talk

about some options to help take the strain off the Pi if the

connection seems a little laggy and how this method can be

used on normal PCs as well, so you can use a range of devices

and get the most from your Raspberry Pi.

01 Update your Raspberry Pi

Before starting, you should absolutely make sure that

your Raspberry Pi is up to date. With the limited resources on the

Pi, any optimisations can make the experience better. You’ll ﬁ rst

want to update the software by opening the terminal and using:

$ sudo apt-get update && sudo apt-get upgrade

… and then follow it up with a ﬁ rmware upgrade by running:

$ sudo rpi-update

02 Install the software

We’re going to be using TightVNC for our VNC needs here

– speciﬁ cally, the server side of the software. We’ll need to install

it ﬁ rst though, so head back to the terminal and type:

$ sudo apt-get install tightvncserver

You may have to run through a setting or two as it installs, hit ‘yes’

(or ‘y’) to them to continue.

06 Correct resolution

We created our test server with a resolution of 640 x 480,

just to get it running. However, this is unlikely to be the resolution

of your phone. Luckily, this resolution is not ﬁ xed every time, so

the best thing to do is to look up the resolution of your Android

device and then modify the line used to start up the server. For

example, if you have a 1080p tablet, you would use:

$ vncserver :1 -geometry 1920x1080 -depth 16

-pixelformat rgb565

03 Start up VNC

Once everything’s installed we can actually start up the

VNC server – it’s probably a good idea to do so now and check to

make sure it’s all working. We’ll do a test run with the following:

$ vncserver :1 -geometry 640x480 -depth 16

-pixelformat rgb565

As long as everything is installed correctly, it should start without

any problems at all.

04 First time setup

The ﬁ rst time you turn it on, you will have to set a

password. You’ll need to pick a password you can remember as it

will also be used by the client as it connects via VNC. You can only

use a maximum of eight characters for the password though, so

think carefully about how you want to make it secure.

Look up the resolution of your

Android device and then modify the

line used to start up the server

If you ﬁ nd the

server is running

a bit too slow for

your liking, our best

tip is to reduce

the resolution to

something your Pi

can more easily

create a server for.

If that’s not helping,

your network

connection may well

be the issue.

Running

slow

05 Stop and restart

As TightVNC doesn’t quite work like a normal service,

you can’t do a usual service X restart (or equivalent) to turn it off

or whatever you wish to do with it. Instead, if you want to restart

it, you’ll have to manually turn it off and then restart it with the

original command. To kill it, use:

$ vncserver -kill :1

… replacing 1 with the display number that you originally create.

Raspberry Pi Tips, Tricks & Hacks 49

Tips | Tricks | Hacks

Full code

FileSilo.co.uk

50 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

08 Raspberry Pi IP

We need the IP address of your Raspberry Pi so that we

can connect to it. You can get it via two methods – our preferred

method is to open the terminal and use ifconﬁ g to list the status

of the Pi’s network interfaces; this will include the IP address of

whatever is connected. If you’re using wireless to connect, you

can also access the wireless conﬁ g interface (iwconﬁ g) and see

what the wireless has been assigned as an IP.

09 Connect to the Pi

Now that we have the IP address, we can look at

connecting to the Raspberry Pi. Open VNC Viewer and click the

‘+’ sign to set up a new connection. Leave the name blank for the

moment, enter an IP address and choose ‘Save password’. It will

ask for the password when you attempt to connect, after which it

will then save it and not require it in the future.

10 Use VNC

If this is the ﬁ rst time that you are using VNC software,

you will notice that there can be a little lag between what you

do and what happens on-screen. Luckily, you can use your

ﬁ nger on the screen to move the mouse and tap to click, and

the Android keyboard can be used as the keyboard. It can take

a bit of getting used to and is not good for anything that you

need to do fast, but it’s still very useful.

11 Turn it all off

Killing the VNC server, as we talked about in Step 5, can

still be done when connected – your Android device will just

disconnect. The same occurs if you just turn off the Pi. If you

disconnect the VNC client from the Pi though, the server on the Pi

will still be turned on; this means that you can at least reconnect

at any time.

12 Turn server on at startup

Currently, every time you turn on the Pi you’ll have to turn

on the VNC server. There’s no conﬁ g setting or service setting

that we can set to have it turn on by default, so to actually do this

we need to write a script. Create a ﬁ le using nano in the terminal

at the following location:

$ sudo nano /etc/init.d/vncserver

Above VNC Viewer is made by RealVNC, the original developers of VNC technology

07 Get the app

On your Android device, go to the Play Store and look

for VNC Viewer (you can also install it from the web store via this

link: bit.ly/1jCzBRJ). Install it to your device and run it to make

sure it works ﬁ ne. We can now begin to try and connect it to

the Raspberry Pi.

Raspberry Pi Tips, Tricks & Hacks 51

Tips | Tricks | Hacks

13 Write the script

This script will do everything we need it to do, but be sure

to edit the resolution for your speciﬁ c use case:

#!/bin/sh -e

export USER=“pi”

# parameters for tightvncserver

DISPLAY=“1”

DEPTH=“16”

GEOMETRY=“1920x1080”

NAME=“VNCserver”

OPTIONS=“-name ${NAME} -depth ${DEPTH} -geometry

${GEOMETRY} :${DISPLAY}”

. /lib/lsb/init-functions

case “$1” in

start)

log_action_begin_msg “Starting vncserver for user

‘${USER}’ on localhost:{$DISPLAY}”

su ${USER} -c “/usr/bin/vncserver ${OPTIONS}”

;;

stop)

log_action_begin_msg “Stopping vncserver for user

‘${USER}’ on localhost:{$DISPLAY}”

su ${USER} -c “/usr/bin/vncserver -kill :${DISPLAY}”

;;

restart)

$0 stop

$0 start

;;

esac

exit 0

14 Or download it

We’ve also got this ready for you to download and put

right into the /etc/init.d directory. You can download it using:

$ wget http://www.linuxuser.co.uk/wp-content/

uploads/2015/06/vncserver.zip

Unzip it and move it into the correct folder, then make any

modiﬁ cations that you want before heading to the next step.

15 Make the ﬁ le executable

Once the script is written, customised to your liking and

saved, we now need to make it executable. To do this, use:

$ sudo chmod +x /etc/init.d/vncserver

As long as it is in the right place and named properly, this will

make it executable. This command is also good to remember in

general as it enables you to make any script executable.

16 Update and test

The ﬁ nal step is to update the ﬁ le rc.d (which handles

startup scripts and such) so that it knows our new script is

there. Do this with the following:

$ sudo update-rc.d vncserver defaults

You can then also test it by using the following to make sure it

works and also to turn it on for this session:

$ sudo /etc/init.d/vncserver start

You can use this

setup with other

systems as the

client – your PC, a

laptop, anything that

you can put VNC on.

It will use the same

settings for each

device though (such

as resolution and

colour depth), and

you can’t each have

a separate screen

to work from. This

can be a good way

to connect to a ﬁ le

server Pi or similar.

Other

VNC clients

Above It‘s simple enough to get around the GUI

using your phone, but for extended bouts of

typing, consider a portable Android keyboard

52 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

Don’t pay for web hosting. Conﬁ gure your Raspberry Pi to

act as a web server and host modest websites

Host your own website

on Raspberry Pi

Need a lightweight, low-cost web server? Your Raspberry

Pi is all you need! Whether you’re planning on hosting a static

homepage (or one with minimal database use) or need an easy

home for development websites, setting up your Raspberry Pi as

a web server is surprisingly easy.

Ideal as an always-on device thanks to its low-power

requirements, the Raspberry Pi can sit beside your router and

serve a basic website to visitors, allowing you to put hosting fees

to better use. You might wish to serve pages for some of your Pi

projects, or even a personal page to host photos or your CV.

If you’re planning on using it as a web-facing device, your Pi

will need to be set up with a static IP address. You’ll also need to

ensure your internet provider offers static IP addresses for their

users. Often a price is charged for leasing a static IP, but there are

services you can use (such as noip.com).

01Connect your Ethernet cable

For this project it makes more sense to use an Ethernet

cable. You may need your existing USB ports to attach ﬂ ash

drives or an external HDD to serve your web page. With Ethernet

you will need to rule out any wireless issues that are causing

interruptions for your visitors.

02Get Raspbian updates and Apache

As ever, begin by checking for Raspbian updates:

sudo apt-get update

You’ll then need to install Apache and PHP:

sudo apt-get install apache2 php5 libapache2-mod-php5

Finally, restart Apache:

sudo service apache2 restart

Your Raspberry Pi is now ready to be used as a web server.

What you’ll need

Q Latest Raspbian image

raspberrypi.org/downloads

Q Internet connection

Q External hard drive

(optional)

Q USB ﬂ ash (optional)

Q Ethernet cable for reliability

Raspberry Pi Tips, Tricks & Hacks 53

Tips | Tricks | Hacks

03 Check your Pi web server

With Apache installed, open the browser on another

computer on your network and enter your Pi’s IP address to

view the Apache conﬁ rmation page.

As things stand right now, all you will be able to view is the

Apache index.php page. To add your own HTML and PHP pages,

you will need FTP.

04 Install FTP for uploading ﬁ les

Create a www folder, then install the following vsftpd

FTP server software:

sudo chown -R pi /var/www

sudo apt-get install vsftpd

You’ll need to make some changes to Very Secure FTP Daemon,

so open it in nano. First, switch:

anonymous_enable=YES

…to…

anonymous_enable=No

Next, uncomment the following by removing the # symbols:

#local_enable=YES

#write_enable=YES

05 Restart the FTP Server

Complete conﬁ guration of the FTP software by

adding a command to the end of the ﬁ le which will display

server ﬁ les starting with “.” such as .htaccess:

force_dot_files=YES

Save and exit nano (Ctrl+X) and restart FTP:

sudo service vsftpd restart

Using the default Raspbian credentials you can upload ﬁ les to

/var/www.

06 Make Pi a LAMP server

By adding MySQL into the mix you can use the Pi to host

a database-driven website or even WordPress (although this is

best limited to using the device as a development server).

sudo apt-get install mysql-server mysql-client

php5-mysql

The LAMP bundle is useful of course, but for the best results your

site should remain streamlined.

07 Get your site online

Can’t afford a static IP for your router? A great solution

is available with the free service from www.noip.com.

This enables you to point a hostname at your computer

by using a client application that will remain in contact with

the No-IP servers.

08 Install No-IP

Make a new directory and switch it to:

mkdir /home/pi/noip

cd /home/pi/noip

Download No-IP on your Pi with:

wget http://www.no-ip.com/client/linux/noip-duc-

linux.tar.gz

Extract:

tar vzxf noip-duc-linux.tar.gz

Next, navigate to the directory and use sudo make and sudo

make install, following any instructions. Finish by running:

sudo /usr/local/bin/noip2

09 Change your password for security

Before using your Pi as a live web server, it’s a good

idea to change the default password to something more

imaginative than ‘raspberry’.

In the command line, enter passwd and then follow the

prompts to add your new, secure password. You’re doing this

step because you obviously would not want your Pi web server

to get hacked!

You can upload files

to /vav/www

54 Raspberry Pi Tips, Tricks & Hacks

Concerned about the security of data stored on

your Raspberry Pi? Protect yourself with passwords,

ﬁ rewalls and some physical security

Secure your Raspberry Pi

There is a distinct security risk around

your Raspberry Pi. Storing anything

from passwords to ﬁ rewalls, this

important saved data can be stolen

or pocketed with minimal effort if

someone knows how.

Therefore it’s a relief to learn that

several tools, tricks and methods

can be applied to keep your device

and data away from prying eyes. You

might, for example, be running a home

security cam with images uploaded to

a cloud account. These images would

What you’ll need

Q Velcro

Q Adhesive putty

Q Lockable cupboard,

strongbox, etc.

Left Running a

private cloud? Make

sure no one can

break into it…

be visible to anyone who possesses

your Raspberry Pi’s login details if

you haven’t bothered to change the

defaults. Such a project (and many

others) also demands that a ﬁ rewall is

installed for further improved security

on a network.

Whether you’re simply changing

passwords, keeping your Pi under lock

and key or installing a ﬁ rewall, you’ll

be surprised at how easy it is to secure

your Raspberry Pi and protect all of your

important information and ﬁ les.

Raspberry Pi Tips, Tricks & Hacks 55

Tips | Tricks | Hacks

01 Stop using the default password

Everyone who uses a Raspberry Pi knows that the

default Raspbian credentials are ‘pi’ and ‘raspberry’. Naturally,

this means that anyone can sign into your computer if you

haven’t changed these defaults – something you’ll need to do as

a matter of urgency. After signing in, open the terminal and set a

new password with:

passwd

04 Give the new account a password

With the new account set up, the next step is to set a

password. As you’re not signed into the account at this stage,

you won’t be using the passwd command. Instead, enter:

sudo passwd username

With the new account ready to use, you should be ready to

remove the default pi account from Raspbian altogether.

03 Create a new user account

To completely baffle anyone attempting to gain access

using default credentials, take the most secure option and create

a new user account. In the command line, enter:

sudo useradd -m username -G sudo

The –m switch creates a new home directory, while the second

sudo adds the new account to the superuser group.

02 Change password with raspi-conﬁ g

If you’re setting up a new installation of Raspbian,

changing the password is one of the ﬁ rst things that you should

do. With a new install, the ﬁ rst boot will automatically run the

raspi-conﬁ g screen.

Here, use the arrow keys to ﬁ nd the second option, change

User Password and then follow the on-screen prompts to set

yourself a new passcode.

With a desktop computer

and SD card reader, there

is a way that you can

recover your password

If you’re genuinely

concerned about

your Raspberry Pi’s

physical security,

you may consider

employing some

additional hardware

to make it less of

a target.

Your best option

here is probably a

proximity sensor

conﬁ gured to detect

an unauthorised

presence. When

coupled with a

buzzer, this can

detect the presence

of an intruder and

alert you. It’s even

possible to conﬁ gure

such an alert as an

email message if

you’re likely to be

elsewhere, and it

makes for a great

side project.

Use a

proximity

sensor

05 Delete the default Raspbian account

You no longer need the default user account, pi. Sign

out and login to your new account, and conﬁ rm it is correctly

set up by opening:

sudo visudo

…and adding…

username ALL=(ALL) NOPASSWD: ALL

…to the ﬁ nal line. Save and exit with Ctrl+X. Now that’s done,

simply delete the old account with:

sudo deluser pi

Then remove the home directory:

sudo deluser -remove-home pi

06 Recover a lost password

If you’ve somehow forgotten your Raspberry Pi user

account password or suspect that someone has changed it,

what can you do?

With a desktop computer and SD card reader, there is a way

that you can recover your password. Begin by inserting the

Pi’s SD card into your PC’s card reader.

Tips | Tricks | Hacks

56 Raspberry Pi Tips, Tricks & Hacks

08 Change the lost password

Unfortunately you won’t be able to use SSH to recover

the password, so instead connect a monitor and keyboard to

your Raspberry Pi. Boot the Pi and wait for the prompt, at which

point you should enter:

passwd username

Type the password, hit Enter and type it again to conﬁ rm.

09 Initialise the Raspbian boot

Thanks to the added code, we have changed the

standard Raspbian boot to display a new prompt that will let us

change the password.

When this is done, enter the following command to put things

back in order:

sync

exec /sbin/init

The Pi will now boot Raspbian normally, enabling you to sign in

with the new password.

10 Revert cmdline.txt

We are not done yet though. Safely shutdown your

Raspberry Pi with:

sudo shutdown -h now

With the Pi powered down, remove the SD card and insert it into

the card reader again. Open cmdline.txt in your text editor once

again and remove init=/bin/sh, then save and exit. This stops

anyone else from resetting your password.

11 Physically secure your Raspberry Pi

Keeping digital intruders out of your Raspberry Pi with

ﬁ rewalls and secure account passwords is only part of the story.

To fully protect your Pi you need to think outside of the box.

Barely larger than a credit card, the Raspberry Pi computer

can easily be picked up and palmed. Physical security is

paramount, but a genuinely secure Raspberry Pi case – for

example, one compatible with Kensington locks – has yet to be

released. However the ProtoArmour aluminium case from www.

mobileappsystems.com can be screwed to a secure surface,

which is great for more permanent project setups.

Putting your

hardware out of

sight and/or out

of reach is a good

option for security,

and for something

as small as the

Raspberry Pi and

an SD card you have

quite a few options.

For instance, using

Velcro or some

adhesive putty you

might attach the

computer to the

back of a cupboard

or unit, kitchen

kickboards or even

under a car seat. The

SD card, meanwhile,

is so compact that

you could easily

place it under a

carpet or even make

a home for it in a

cushion or shelf –

just don’t forget

where you put it!

Hiding

hardware 07 Edit cmdline.txt

Find the ﬁ le cmdline.txt and open it in your Linux

desktop text editor. Add the following to the end of the last line

of the ﬁ le:

init=/bin/sh

As the Raspberry Pi boots, this command will be read,

enabling us to access a screen to reset the password. Save

and eject the card.

Fwbuilder has a

great quick-start

guide that handily

annotates the

entire interface

The objects in

this panel can be

dragged out into

the rules panel on

the right-hand side

Several ﬁ rewall

templates are

available for the

most common

types of setup

Raspberry Pi Tips, Tricks & Hacks 57

Tips | Tricks | Hacks

12 Lock it in a drawer

Probably the best way to keep your Raspberry Pi secure

is to make sure you keep it locked in a drawer or cabinet –

particularly useful if you use the device as part of a security

cam system or as a cloud server storing valuable documents.

If no lockable storage is available and you’re taking some

time away from home where it isn’t practical to take the Pi with

you, another solution is needed. This might be to travel with

your Pi’s SD card in your wallet, perhaps leaving the computer

attached to the back of a wardrobe with Velcro.

13 Add a ﬁ rewall

Regardless of which operating system you’re using,

adding a ﬁ rewall is a guaranteed way to improve your

computer’s security. While the Raspberry Pi has a built-in

ﬁ rewall, it is tricky to conﬁ gure.

Thankfully, some other people have noticed this too and

released fwbuilder, an interface to the otherwise complex

iptables ﬁ rewall that comes with Raspbian.

14 Install fwbuilder in Raspbian

Because iptables is a bit ﬁ ddly and errors can

leave you with no network connection, fwbuilder has been

developed to make ﬁ rewall conﬁ guration quick and painless.

We’ll use the apt-get command to ﬁ rst check for updates

and then install fwbuilder:

sudo apt-get update

sudo apt-get install fwbuilder

Follow the prompts to install and, once complete, switch to

the Raspberry Pi GUI by entering:

startx

In the Pi’s mouse-driven desktop, launch fwbuilder from

the Internet menu. Upon launching fwbuilder, follow the

given steps to set up your Raspeberry Pi ﬁ rewall and save

the resulting script.

We’re nearly done but some adjustments are still required

before your Pi fully connects to the network.

15 Complete ﬁ rewall conﬁ guration

Launch the /etc/network/interfaces script in your text

editor and complete conﬁ guration by adding

pre-up /home/pi/fwbuilder/firewall.fw

Next, ﬁ nd the section labelled “Epilog” and add

route add default gw [YOUR.ROUTER.IP.HERE] eth0

If you’re using a wireless card, add the same line but switch

the last characters to wlan0:

route add default gw [YOUR.ROUTER.IP.HERE] wlan0

16 Consider Raspberry Pi theft

While losing your Raspberry Pi or the data on it, might

initially seem like a disaster, don’t be disheartened. As long as

you have taken steps to backup data or clone your SD card,

you at least have continuity when you resume the project.

You can also check our boxouts for methods to help you deal

with physical theft.

If you’re still

concerned with

your Pi’s safety, put

yourself in the place

of a potential thief.

Where would you

stash it? Probably

in your pocket. The

Raspberry Pi is small

enough to take with

you, so why leave it

lying around? Any

security questions

relating to your

Raspberry Pi can

be addressed by

keeping it close

whenever you think

it’s necessary.

Pocket

your Pi

Below If you tend to access your Pi

remotely via Wi-Fi, consider keeping

it locked away

A ﬁ rewall is guaranteed to

improve your security

Tips | Tricks | Hacks

58 Raspberry Pi Tips, Tricks & Hacks

The Raspberry Pi is small, silent and energy efficient,

so let’s turn it into the ultimate file server!

Build a file server

with the Raspberry Pi

router’s IP address, meaning that you can access

your Raspberry Pi from anywhere using an easy-to-

remember web address

• Transmission daemon – a torrent client that runs

in the background and can be accessed through a

web browser

This tutorial assumes that you have ﬂ ashed

the latest Arch Linux ARM image to an SD card. If

you haven’t done this, the instructions for ﬂ ashing

an image can be found at www.linuxuser.co.uk/

tutorials/how-to-set-up-raspberry-pi/.

You’ll only need to go up to the step that involves

writing the image to the SD card – or if you plan to

use the SD card to store ﬁ les, then you should follow

the GParted steps also. Not that you’ll also have to

adapt the instructions slightly for using the Arch

Linux image rather than the Debian one.

We’ll be using Arch Linux as the operating system for

our file server, because it is small, and has only the

minimum packages required for a working system.

This means that we can set up the file server without

wasting resources on a graphical user interface and

other unnecessary packages. Arch Linux comes with

hardly any RAM allocated to the GPU by default, which

is exactly how we want it for use as a headless server.

Our ﬁ le server will be made up of the following

software components:

• Base Arch Linux system

• SSH – will provide secure remote access to the

Raspberry Pi and the ﬁ les on it

• Samba – provides access to ﬁ les on the server to a

Windows, Mac or Linux client

• A dynamic DNS daemon (noip) – software that runs

in the background and points a domain name to your

Raspberry Pi

A powered USB hub which

provides power and USB

connectivity to two

2.5-inch hard drives

Two 2.5-inch hard drives.

Your advisor has a 320GB

Western Digital USB drive;

the second drive is an 80GB

from an old laptop which he’s

converted to a USB drive using

an IDE-to-USB converter

An 8-port Netgear switch

which the Raspberry Pi is

connected to, along with our

other computers and devices

www

What you’ll need

Q Raspberry Pi with all necessary

peripherals

Q SD card containing the latest

Arch Linux image for RasPi: www.

raspberrypi.org/downloads

Q Powered USB hub

Q External hard drive or pen

drive

Q A computer running Linux – it

can be another Raspberry Pi

Raspberry Pi Tips, Tricks & Hacks 59

Tips | Tricks | Hacks

01 Log into Arch Linux

Connect the necessary cables to the

Pi and wait for the Arch Linux login prompt.

The login is root, and the password is also

‘root’. We’ll change the root password from the

default later on.

02 Run a full system update

Arch Linux runs on a rolling release

schedule, meaning that there are no version

numbers and software is continually updated. Use

the command ‘pacman -Syu’ to start a full system

update. You’ll be shown a prompt explaining that

pacman needs to be updated first. Answer ‘Y’ to

the prompt. You can now run ‘pacman -Syu’ again

to start a full system update. There will be a lot of

packages to update so it will probably take a while,

especially because the Pi runs from an SD card.

03 Investigate your network

We highly recommend assigning a static

IP to your Raspberry Pi rather than being handed

one by your router because you’ll always know

where to ﬁ nd it on the network, which will be

useful for accessing it remotely. You’ll also need

a static IP if you want to access the Raspberry Pi

from the internet. We’ll need to ﬁ nd out a couple

of things about your current network setup before

setting a static IP. You can use the commands

‘ifconﬁ g eth0’ and ‘ip route show’ to do this.

04 Set up a static IP address

Now that we have found out things

about your network, such as your current IP

address, the network mask and so on, we

can set up a static IP address. The majority

of the Arch Linux conﬁ guration is done from

a ﬁ le called rc.conf, which is located in the

/etc directory. You can open this ﬁ le in the nano

editor with the command ‘nano /etc/rc.conf’.

Scroll down using the arrow keys until you come

to the networking section.

Begin to ﬁ ll in the blank eth0 section. Our IP

address was 192.168.1.215. When assigning an

IP address, you’ll only want to change the last

number. We’re going to change our address

05 Log in with SSH

We’ll now log into the Pi using SSH – but

before that, we’ll restart so that the static IP

and any updates take place. Use the command

‘init 6’ to do this. Once the Pi has booted back

up, open a terminal on your Linux computer

and type ‘ssh root@[ip of your pi]’. Answer yes,

to say that you want to connect, and type in the

root password, which will still be root. You are

now logged in over SSH.

07 Change the root password

Since we might be exposing an SSH login

to the internet, we need to change the password to

a more secure one. Type ‘passwd’, then follow the

on-screen instructions to change your password.

Your SSH session will stay logged in, but you’ll need

to use the new password next time you log in.

06 Set the default gateway

This step is really part of step 4 (set up a

static IP address). The reason for doing this step

after restarting, is that we found the changes

were lost when we did it before a restart. This is

probably due to DHCP cleaning up any settings it

changes during shutdown. We will now set the IP

of the DNS server, which will be used to resolve

addresses such as google.co.uk to an IP address

that your computer can connect to. Your DNS

server will be provided by the same IP as your

default gateway. You can set the DNS server

using the following command:

echo ‘nameserver [ip of default

gateway]’ > /etc/resolv.conf.

09 Formatting your hard drive

Before continuing, note that formatting

a disk will remove all the data on it. It’s now

time to connect your hard drive to the Pi. (We’re

using a pen drive, but the steps are exactly the

same.) Use the command

fdisk -l | grep Disk

to get a list of disks attached to the system.

You should be able to tell which disk is the one

you intend to use to store ﬁ les on by the size of

the disk. For example, our pen drive is 16GB, so

we know that the 16.1GB disk is ours. Run the

following command:

(echo o; echo n; echo p; echo 1;

echo ; echo; echo w) | fdisk [path

to your disk]

to create a partition that will be whole size of

the disk. Fdisk is an interactive program, so this

command simply inputs the keys that you would

press in a speciﬁ c order to create a partition that

will take up the whole size of the disk.

08 Install the required packages

Use the command ‘pacman -S samba

noip transmission-cli’ to install the required

packages mentioned at the start of the article.

Answer ‘Y’ to any prompts you may encounter.

to 192.168.1.191. You’ll probably want to use a

number between 100 and 200. Set the netmask

and broadcast to the values from ‘ifconﬁ g eth0’

so that the interface is conﬁ gured correctly

for your home network. Set the gateway to

the address in the line similar to default via

‘192.168.1.254 dev eth0 metric 202’ from the

output of ‘ip route show’. Once you have done

this, use the key combination Ctrl+O followed by

the Enter key to save the changes. You can then

use Ctrl+X to exit nano.

60 Raspberry Pi Tips, Trick & Hacks

Tips | Tricks | Hacks

11 Make the drive accessible to Linux

The fstab ﬁ le on Linux system contains

a list of storage devices on the system, and

where to mount them. The ﬁ le is read on boot,

so any devices in the fstab ﬁ le will be mounted

automatically as long as it is connected

during boot.

We’ll edit the fstab in nano using the

command ‘nano /etc/fstab’. You want to add a

line like the following:

[path to disk]1 /mnt/data ext4

defaults 0 1

Save the changes in the same way we did

earlier. Once you have done this, you can use

the command ‘mount -a’ to reread the fstab ﬁ le

and mount the new entry we just added.

14 Conﬁ gure the Transmission

torrent daemon

We’ll need to start the Transmission daemon

because we’ll need to edit some conﬁ guration

ﬁ les that it will only make on ﬁ rst execution.

Start it using the command:

/etc/rc.d/transmissiond start

You’ll then want to stop it using the command:

/etc/rc.d/transmissiond stop

so that we can edit the conﬁ guration ﬁ le

without Transmission interfering. Open the

conﬁ guration ﬁ le using the command:

nano /root/.config/transmission-

daemon/settings.json

You need to set rpc-whitelist-enabled from

true to false, and also change the download-

dir to /mnt/data/Downloads. You can then

save the changes and make that directory

using the command:

mkdir /mnt/data/Downloads

15 The Transmission web interface

We can now start the Transmission

daemon using the same start command

from the previous step. Transmission can

sometimes be a bit picky with the syntax of its

conﬁ guration ﬁ les, so now that you’ve started

13 Permit access to the shared drive

Set a password for your Samba user

using the command ‘smbpasswd -a’ and then

enter the password you want to use twice. Now

that we’ve done that, we can start the Samba

daemon using the command

/etc/rc.d/samba start

Note that the method of accessing a Samba

share from each operating system will be

different, so you may have to look it up. It

Input the following information:

[global]

# workgroup = NT-Domain-Name or

Workgroup-Name, eg: MIDEARTH

workgroup = WORKGROUP

security = user

load printers = no

# Some performance tuning

socket_options = TCP_NODELAY SO_

RCVBUF=65536 SO_SNDBUF=65536

[data]

path = /mnt/data

public = no

writable = yes

Save the changes in the same way we did earlier.

12 Share the drive with

network clients

We need to open an empty Samba conﬁ guration

ﬁ le in nano using the command

nano /etc/samba/smb.conf

10 Create a ﬁ le system & mount point

Once we have a partition on the disk,

we need to create a ﬁ le system and a place to

mount it. You can create an ext4 ﬁ lesystem on the

partition using the command

mkfs.ext4 [path to disk]1

You can make a directory to mount the drive in

using the command

mkdir /mnt/data

should show up as ‘ALARMPI’ in the Network

browser on most operating systems and user-

friendly Linux distributions. Use the username

‘root’ and the password that you set with the

smbpasswd command.

Fig 1 Testing out Transmission

The Transmission web interface

is straightforward to use

Raspberry Pi Tips, Tricks & Hacks 61

Tips | Tricks | Hacks

18 NAT port forwarding

It is likely that there are multiple devices

behind your router that all use the same external

IP address. This is because of the shortage of IPv4

addresses, and also because it is more secure to

segregate the internet from your internal home

network. NAT (network address translation)

forwards a port from the router’s external IP

address to a computer on the LAN (local area

network). In this case, we’ll want to forward any

trafﬁ c for port 22 that comes to your router’s

external IP address to the IP address of your

Raspberry Pi. Port 22 is the port used for SSH,

which is the only port we’d recommend that you

forward. SSH will provide access to your ﬁ les,

and also port forwarding, so you can access the

Transmission web interface should you want to.

The conﬁ guration of port forwarding really

depends on the router that you are using, so

you may have to look up that information. The

chances are that it will be hidden away in the

‘advanced’ section of your wireless router. You

should be able to access your router by typing

your No-IP hostname into your web browser. If

not, it should be at the address of your default

gateway that we used earlier on.

On his router, your advisor had to go to

Advanced>NAT>Port Mapping and add a mapping

that looks like that in Fig 2.

20 Use SSH to port forward

Use the SSH command with the

following option to forward any trafﬁ c from

127.0.0.1:9091 to 126.0.0.1:9091 on the Pi:

ssh -L 9091:127.0.0.1:9091

root@192.168.1.191

(You can replace the IP address of the Pi with

your No-IP hostname if you are outside of your

LAN.) 127.0.0.1 is a loopback address, which

points back to ‘this computer’.

Once you have run that command, you

can then go to the web browser on your

computer, type in 127.0.0.1:9091 and access the

Transmission web interface as if it was on the

LAN. Now, you are ready to enjoy your brand

new ﬁ le server!

package manager, to access ﬁ les via SSH. Set

the host to the IP address of your Pi (or your No-

Ip hostname if outside your LAN), the username

to ‘root’, and the password to your password. Set

the port to 22 and click ‘Quickconnect’. Click OK to

trust the host and connect to it. To access ﬁ les on

your external drive, change remote site from /root

to /mnt/data.

it, you’ll want to check that your conﬁ guration

changes are still there. If not, stop the

Transmission daemon and try again.

You can go to the Transmission web interface

by opening up a web browser and going to

the IP address of your Pi, followed by :9091.

This is needed because the web interface is

served from port 9091. In our case, we used

192.168.1.191:9091. Click on the icon in the

top-left corner of the interface to add a torrent

ﬁ le. You can either upload a ﬁ le from your

computer, or copy and paste a URL. As you can

see from Fig 1 (on preceding page), we have just

added a Raspberry Pi image to test it out.

The Transmission web interface is really

straightforward and easy to use, so you

should be able to ﬁ gure out anything else you

want to do. There is also more documentation

on the settings.json conﬁ guration ﬁ le here:

https://trac.transmissionbt.com/wiki/

EditConﬁ gFiles

16 Set up dynamic DNS

Head over to www.no-ip.com/personal/

and sign up for the No-IP Free option. Once

you have done that, don’t bother downloading

No-IP’s client because we’ve already installed

it. Go to your email Inbox and follow the

activation link that was just sent to you by No-

IP. You can now sign in to your account. Once

you have logged in, select the ‘Add a host’

option. Choose a hostname and a domain to be

part of from the drop-down list. Leave the Host

Type as ‘DNS Host’ and then click the ‘Create

Host’ button.

Your advisor used the hostname liam-ludtest

with the domain no-ip.org, so would access

that using liam-ludtest.no-ip.org.

17 Conﬁ gure No-IP

Run the command:

noip2 -C -Y

…to be taken through interactive conﬁ guration

of the No-IP client. We left the update interval

to the default of 30 minutes, meaning the client

will check every 30 minutes for an IP address

change. Once you’ve ﬁ nished, start the daemon

with the command ‘/etc/rc.d/noip start’. 19 Use FileZilla for accessing ﬁ les

We recommend that you use FileZilla,

which you should be able to install with your

After a minute or two, your IP address will be

accessible via your No-IP hostname. However,

it’s likely that trying it from inside your house

will simply take you to your router’s homepage.

Fig 2 Port mapping example

Tips | Tricks | Hacks

62 Raspberry Pi Tips, Tricks & Hacks

Borrow a mouse and keyboard from another PC, using

only your Raspberry Pi and Synergy

Network and share your

keyboard and mouse

One issue we sometimes find with the Raspberry Pi is the lack

of USB ports. We don’t always have the luxury of using a powered

USB hub, and it can become a bit of a hassle to juggle a mouse

and keyboard with other devices. Instead of using a hardware

solution for this, you can always try a software solution – one

that opens up the uses of the Raspberry Pi as well. The Synergy

program lets you share the mouse and keyboard of one system

with other systems on the same network, acting as a virtual

KVM. In this tutorial we'll learn how to use your main computer's

input devices on your Raspberry Pi, as well as how you can look

into making it a server.

01 Install Synergy

Synergy is available from the

Raspbian repositories. We can install it

by using the following:

$ sudo apt-get update

$ sudo apt-get install synergy

This will go through the basic installation

process as normal and Synergy will be

put in the Accessories folder.

What you’ll need

Q Latest Raspbian Image

raspberrypi.org/downloads

Q Synergy

Q Host computer

Raspberry Pi Tips, Tricks & Hacks 63

Tips | Tricks | Hacks

02 Start up Synergy

Start up Synergy on the host

computer and choose the ‘Server’ option

for the moment. We’ll cover how to use

it as a client later, and how to use the

Raspberry Pi as a server for the mouse

and keyboard.

03 Encryption and passwords

Here, you can set up whether

or not the connection is encrypted. This

is useful for stopping key loggers from

being able to snoop on your information,

or random clients from connecting

and hijacking your mouse. Provide a

password and then click Finish.

04 Server naming

Once the process has ﬁ nished,

go to Conﬁ gure Server. Your host

computer will be put virtually in the

centre of your array of displays and you

can drag and drop it around, along with

any connected screens. Double-click on

the server to change its name, making it

easier to remember and ﬁ nd. Add a new

screen and call it pi.

05 Starting and connecting

Once you’re happy with the setup, click Start to

be able to accept client connections. To connect from a

Raspberry Pi, enter the following:

$ synergyc --name pi [IP Address of host]

It will be recognised as ‘pi’ on the host system.

06 Autostart Synergy

To make sure it starts every time you turn on the Pi, we

need to create an LXDE autostart ﬁ le by using the following:

$ sudo mkdir -p ~/.config/lxsession/LXDE

$ sudo touch ~/.config/lxsession/LXDE/autostart

$ sudo nano ~/.config/lxsession/LXDE/autostart

And then add the following to autostart:

~/.startsynergy.sh

07 Start ﬁ le

Open and populate the startsynergy ﬁ le with:

$ sudo nano ~/.startsynergy.sh

#!/bin/bash

killall synergyc

sleep 1

synergyc --name pi [IP address of host]

exit 0

08 Permissions

Finally, to ﬁ nish it off you’ll need

to run:

sudo chmod 777 ~/.startsynergy.sh

This will autostart, and hopefully

autoconnect, Synergy whenever you turn

it on. The Raspbian client is a little old,

so if you get a problem you may need to

compile the latest version from source.

09 Pi server

Setting up the Raspberry Pi as

a server is a little more involved and uses

the synergys command. It allows you to

listen for clients on speciﬁ c addresses.

You then need to create a separate

conﬁ guration ﬁ le to arrange the displays

– however, you can load one from a

different computer and edit it.

Synergy lets

you share a

mouse and

keyboard

Left Select the Server

option to use this

machine’s mouse and

keyboard for the Pi

Tips | Tricks | Hacks

64 Raspberry Pi Tips, Tricks & Hacks

Need to restart your Pi after a system lock-up? Ease

strain on the mains connector – install a reset switch!

Add a reset switch

to your Raspberry Pi

We all know that shutting down a Raspberry Pi by removing

the power cable is risky. Data may be writing to the SD card,

leading to corruption, while repeated removal of the power cable

can cause problems with the connector port.

Clearly this can cause problems when faults cause the

Raspberry Pi to hang, so the simple ﬁ x here is to add a simple

reset function to the device. There are three ways this can be

done: with a USB reset button, a motherboard jumper on the

GPIO bus or with a momentary button connected to newly-

soldered pins on the P6 header on the Model B Rev 2 and B+ (this

is the most complicated option).

If you have an old PC lying around, retrieving the reset button

and cable from this and even the connecting motherboard pins

is achievable if you’re handy with a soldering iron. Otherwise, we

recommend purchasing the parts online, although be aware that

you'll probably need to buy more pins than you'll need.

01Check your Raspberry Pi model

Only two models feature the P6 header: the Raspberry

Pi Model B Rev 2 (which you can ﬁ nd next to the HDMI port)

and the B+ (to the left of the ‘© Raspberry Pi 2014’ label). You

will need to install the pins manually, however, as they are not

preinstalled for this function.

What you’ll need

Q Momentary switch

Q Suitable wire for PCB

projects

Q Soldering iron and solder

Q Single pin pair header

Q HDD/motherboard jumper

Raspberry Pi Tips, Tricks & Hacks 65

Tips | Tricks | Hacks

QYou should

know your Pi

inside and out,

and learn how to

identify GPIO pins

02Find your components

Header pins can be purchased online, although this will

invariably result in having to order more than you need.

Alternatively, if you have an old motherboard, remove a pair

of pins with a soldering iron. Similarly, you might buy a new reset

button, or use one from an old PC.

03 Solder pins to your Pi

To gain stability when soldering, place the Pi upside

down on a layer of packaging foam, with the header slotted into

the holes.

Using ﬁ ne solder, secure the pins to the mainboard with

your soldering iron. This will require a very steady hand, so get

assistance if required.

04 Connect your reset switch

Leave the solder to cool for a few minutes before

attaching the reset switch connector.

Some cases don't have space for the pins and/or the

connector, however, so take the time to plan ahead and

make sure everything ﬁ ts. If not, you may need to make some

adjustments to your case.

05 Reset Raspberry Pi following crashes

With the switch installed, you’ll be able to reset the

Raspberry Pi when required. Note, however, that this isn’t an

option to be used for whenever you feel like restarting. Rather,

it should be done only when the system fails to respond within

a reasonable time frame.

06 Reset with a HDD jumper

Not keen on soldering new pins to your Raspberry Pi?

That is perfectly understandable, but it doesn’t mean you cannot

reset the computer. We have another solution for you.

Using a motherboard jumper, two GPIO pins and a script to

initiate an ordered shutdown is a simple alternative that doesn't

involve solder and potential PCB damage.

07 Identify the GPIO pins

This method works on most models. Each has a GPIO

array, 26 pins on the A and B (Rev 2) and 40 on the A+ and B+.

The jumper should be placed on GPIO3, pins 5 and 6 counting

from the left with the board the right way around.

08 Detect jumper with a script

Use the script at bit.ly/1Ge5n0O to detect the jumper,

making it executable (sudo chmod 755) before running. Within

a minute your Pi will shut down. Add this line to /etc/crontab to

run the script whenever you boot up.

@reboot root /home/user/scripts/gpio_actions.sh

Remember to remove the jumper before booting up!

09 Try a USB reset button

Specialist online stores offer USB reset buttons that

can be connected to your Pi for scenarios when the device

needs to be rebooted.

If the idea of using the HDD jumper or doing some minor

soldering doesn’t suit you, then a USB reset switch might be

your best option.

Shutting down a Raspberry

Pi by removing the power

cable is risky

Tips | Tricks | Hacks

66 Raspberry Pi Tips, Tricks & Hacks

Use a web interface to control your Pi and employ

it as a ﬁ leserver or media centre from a remote

location using any web-connected device

Remotely control

your Raspberry Pi

Not everyone uses the Raspberry Pi

while it’s hooked up to a monitor like a

normal PC. Due to its size and portability,

it can be located almost anywhere

that it can be powered and it’s widely

used as a ﬁ le server, media centre and

for other nontraditional applications.

Some of these uses won’t easily allow

access to a monitor for easy updates and

maintenance. While you can always SSH

in, it’s a bit slower than a full web interface

that allows for custom commands and a

view of the Pi’s performance. We’re using

software called RaspCTL, which is still in

development, but works just ﬁ ne for now.

01Update your Pi!

To make sure the Raspberry Pi works as best it can, you’ll

need to update Raspbian. Do this with a sudo apt-get update

&& apt-get upgrade, followed by a ﬁ rmware update with sudo

rpi-update. Finally, if you’re booting to LXDE, enter raspi-

config and change it to boot to command line to save power.

What you’ll need

Q Raspbian set to

command line

Q RaspCTL

Q Internet connection

Main window Get the full details of

the currently running system from the web

Commands Create custom

commands for running your Raspberry Pi

Other utilities Seeing through your

webcam and setting an alarm are just two

additional things you can do with your Pi

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 67

02Edit the IP

For everything to work more easily, you should set the

Raspberry Pi to have a static IP of your choice. To do this, edit the

networking conﬁ g by using:

$ sudo nano /etc/network/interfaces

…and change iface eth0 inet dhcp to iface eth0 inet static.

03 Set up a static IP

Add the following lines under the iface line with your

relevant details:

address 192.168.1.[IP]

netmask 255.255.255.0

network 192.168.1.0

broadcast 192.168.1.255

gateway 192.168.1.[Router IP]

04 Ready to install

You’ll need to grab the public keys for the software

we’re going to install by using the following commands. The ﬁ rst

will take just a moment to download the software, while the

other quickly installs it:

$ wget debrepo.krenel.org/raspctl.asc

$ cat raspctl.asc | sudo apt-key add -

05 Add the repository and install

Add the repository to the source’s ﬁ le with the

following command:

$ echo “deb http://debrepo.krenel.org/ raspctl

main” | sudo tee /etc/apt/sources.list.d/raspctl.

list

…and ﬁ nally install the software with:

$ sudo apt-get update

$ sudo apt-get install raspctl

06 Access your Raspberry Pi

Now the software is installed you can start to access

your Raspberry Pi from anywhere on your network. To do this

type the following into your address bar, with the IP being the one

we set up earlier:

http://[IP]:8086

07 Change your password

The default username and password is admin for both

ﬁ elds, and you should make sure to change that before doing

anything else. Go to Conﬁ guration along the top bar and ﬁ nd

the Authentication ﬁ eld at the bottom of the page. Input the

original password (admin), followed by your new passwords.

The username will remain as admin.

08 First command

Go to Commands on the top bar to begin creating

commands to run. Here you’ll need to add a class – a user-

deﬁ ned way to ﬁ lter your commands that won’t affect the way

it’s run – a name for the command and the actual command

itself. The commands won’t necessarily run from the pi user

unless you tweak the conﬁ g ﬁ les.

09 More functions

The web interface has a few extra functions apart from

running commands, such as the ability to view the webcam and

connect to radio services. Updating the software every so often

will also allow you to make sure it keeps working. Play around

with it and see what best suits you.

Android ports are

now available for

Raspberry Pi, opening

up a whole new world of

possibilities. Here’s how

to get started…

Raspberry Pi

on your

Android

Install

68 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

While one of the main reasons for the creation of the

Raspberry Pi was to offer a cheap way for people to get

into programming and using Linux, there are plenty of

people who see it being used as a replacement for other

forms of computing tasks. With the Pi being so small, the

concept of using it for purposes where space is a premium

is deﬁ nitely not too far-fetched. Its form factor, weight and

low power requirements make it ideal for use in a number

of situations; however, the software may not always be

the best for the task. Where Linux may be lacking, though,

Android is there to cover it.

Android ports to Raspberry Pi have been in the works for

a little while now, but they’ve only just been made a usable

reality thanks to the recent open-sourcing of the VideoCore

GPU driver code. This allows for full hardware acceleration

of Android, something that was previously having to be done

purely by the CPU.

Android can offer a very different experience and

interface than a standard Linux distribution, without having

to obtain custom distros so it’s optimised for a particular

use. This means you can experiment with the sort of

applications you’d want to use Android for without carrying

around multiple SD cards in lieu of wiping them every time.

Thanks to an ever growing development community,

Google recently announced that there had been 25 billion

Android app downloads by the end of September, ﬁ ve

billion up from the number at the end of July, from its

675,000-strong selection. With this rate of expansion, there

are always a number of apps for pretty much anything you’d

want an Android device to do. With access to this range of

possibilities on the Raspberry Pi, you can create a system

that has the advantages of using a mobile, user-friendly

OS, with the price of the Pi. And the addition of more I/O

ports from the Pi can make it ﬁ t in better than your standard

Android smartphone.

There are three types of projects we’re going to cover over

the next few pages: a smart TV, a home automation remote

and an in-car computer. While such distros like XBian and

OpenELEC exist for media centres and home theatre PCs

using the Raspberry Pi, the XBMC apps do not have the

same kind of range as Android. With apps going outside the

concept of plain media watching, and even the inclusion

of Android games, there’s a lot more you can do with an

Android-run smart TV.

For home automation, there are very mature X10 and

Z-Wave remote control apps available on Android that are

optimised for the kind of interface you’d want to use for a

remote control, unlike the mainly mouse-focused tweaking

tools used on Linux distros. Finally, with in-car computers,

the touch-screen optimisations and grid array for apps

allow for easy navigation to music, podcast and other

media apps, as well as plenty of fantastic GPS and satellite

navigation applications native to Android.

Q All you need

is a Raspberry

Pi set up and

ready to go!

Meet Razdroid

The team makes the ﬁ rst project to

get Android on your Pi

Before the release of the VideoCore

drivers, some community members

decided they wanted to have a go

at porting Android to Raspberry Pi,

creating Razdroid. Based mainly on

CyanogenMod, the project got far enough to have a couple

of working ports, only limited by the lack of hardware

acceleration. Since then, the Raspberry Pi Foundation

has created its own ports, and eventually released the

VideoCore driver to make ports of Android and other

software a lot smoother.

Raspberry Pi Tips, Tricks & Hacks 69

Tips | Tricks | Hacks

You can put Android on your Raspberry Pi

right now by visiting the Razdroid site at

www.razdroid.net. There are currently a couple

of images, based around both CyanogenMod 7.2

and 9, with different performance capabilities

and app compatibility. The images can be put on

an SD card using the same method as you would

a Linux distro image, and will run from boot

without any extra setup needed.

If you’re feeling a little more adventurous, you

can compile the images from source instead.

You’ll be able to make changes, updates and

additions as well, if you want to improve the

build. The steps on this page will guide you

through a basic build of CyanogenMod 7.2,

based on Android 2.3, for the Raspberry Pi, using

the same ﬁ les as the Razdroid image to get

it working.

Q Using a standard dd operation, you can get your Raspberry Pi running Android

01 Install libraries

You’ll need to get the necessary

libraries for the build to work:

$ sudo apt-get install git-core

gnupg flex bison gperf build-

essential zip curl libc6-dev

libncurses5-dev:i386 x11proto-

core-dev libx11-dev:i386

libreadline6-dev:i386 libgl1-

mesa-glx:i386 libgl1-mesa-dev

g++-multilib mingw32 openjdk-6-jdk

tofrodos python-markdown libxml2-

utils xsltproc zlib1g-dev:i386

$ sudo ln -s /usr/lib/i386-linux-

gnu/mesa/libGL.so.1 /usr/lib/i386-

linux-gnu/libGL.so

CC: Jim Killock

It’s easy to install Android…

When the Raspberry Pi was ﬁ rst created, there were some

very speciﬁ c goals in mind for the ﬁ nished product. Thanks

to the way it met these goals, it has blown up as the darling

of hobbyists and other tech enthusiasts for all manner of

projects. To further understand the relationship between

the original goals and this new concept of putting Android

on the Raspberry Pi, we spoke to the co-creator of the

Raspberry Pi himself, Eben Upton.

Upton told us that there had never really been any plans

originally for Android to be supported by the Raspberry

Pi. However, developments in recent times had changed

the view of the Foundation: “A signiﬁ cant minority of our

customers want to see it, so that makes it important to us.”

When the Foundation originally announced it was

working on Android compatibility, it already had a working

prototype. “This implementation uses a different kernel

and VideoCore binary image from the one available on

GitHub,” explained Upton, “which is why we’ve been

keeping quiet about it so far.” This was in late July, and it

took the Foundation a further three months to ﬁ nally get

the VideoCore drivers open-sourced. Upton told us shortly

before its release why it had been delayed so long: “The

issue around releasing the Broadcom Android version is

that we’d need a separate microcode image for the GPU,

and we really don’t want to fork the community.”

Eben Upton

speaks

Follow our step-by-step guide to get up and running

Without Eben Upton, the Raspberry Pi

would not have been possible. Coming

from a background of computing and

teaching, Upton is currently a technical

director at Broadcom and is responsible

for the overall software and hardware

architecture on the Raspberry Pi.

The co-founder of the

Raspberry Pi Foundation

70 Raspberry Pi Tips, Tricks & Hacks

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Raspberry Pi Tips, Tricks, & Hacks 71

www.linuxuser.co.uk

Q The Play Store will

initially be missing

from any ports

03 Build environment

Now we’ll make a directory for the

build environment and initialise it for the repo

sync. First:

$ mkdir ~/android_pi

Then move to it and initialise:

$ cd ~/android_pi

$ repo init -u git://github.

com/CyanogenMod/android.git -b

gingerbread

And ﬁ nally sync:

$ repo sync -j16

04 Device tree

After the sync has ﬁ nished, create a

new directory and download the device tree for

your build:

$ mkdir -p ~/android_pi/device/rpi

$ cd ~/android_pi/device/rpi/

$ git clone https://github.com/

Mathijsz/device_rpi.git

$ mv device_rpi rpi

06 The build

We’re now ready to build our Razdroid

image. Make sure to do following to start

the build:

$ source build/envsetup.sh

$ lunch

$ make -j4

Be aware that this may take a while.

02 Working directory

We need to download the source to

a folder that we can make executable. First

create the directory:

$ mkdir ~/bin

Then add it to your path:

$ PATH=~/bin:$PATH

And ﬁ nally, download and chmod:

$ curl https://dl-ssl.google.com/

dl/googlesource/git-repo/repo > ~/

bin/repo

$ chmod a+x ~/bin/repo

05 Initial setup

Before we do the actual build, we need

to run a little script to properly prepare the

source code:

$ cd ~/gingerbread_pi/device/rpi/

rpi

$ ./initial_setup.sh

$ cd ~/gingerbread_pi

This will automatically make the changes.

Now the source code has been released, via the ARM

Userland on GitHub, and marks the ﬁ rst time a full ARM-

based, multimedia SoC has received vendor-provided open-

sourced drivers, and Broadcom is the ﬁ rst company to open

up its mobile GPU drivers in this way. With it, people can get

down to ﬁ nishing Android ports and starting new ones.

Android is well known as being used on touch-screen

interfaces, but earlier devices included keyboards

and trackballs. While this has gone out of vogue for

smartphones and other handheld devices, for testing out

your Android-powered Pi it would be useful to have this

option. Is it available now, though?

“I’m not aware of any signiﬁ cant challenges in this area.”

Upton told us when we asked about traditional inputs. “We

expect most people would use Android with a mouse and

keyboard, and this seems to be a well-supported option

from ICS (Android 4.0) onward.”

So with this native mouse and keyboard support,

you’re going to be able to ﬁ nd a lot more applications for a

Raspberry Pi running Android than you could do with even

an Android smartphone. On top of that, you will likely get

the same kind of performance as a Linux distro according

to Upton: “I would expect them to be very close in terms

of performance. There may be more UI acceleration in

Android, though, which we hope to bring into Linux.”

Finally, one of the main reasons to use Android would be

to access the huge array of apps. We asked Upton about the

issue with Google Play – those into the Android scene

might know that CyanogenMod had to remove this

from the standard build for legal reasons. Upton

told us there were currently no plans to obtain

a licence for the store; however, Android

allows you install the APK ﬁ les

without the store, and these are

usually very easy to obtain.

Q The concept

of the Raspberry

Pi is a spiritual

successor to the

BBC Micro

Tips | Tricks | Hacks

Smart TV

Use your Raspberry Pi to

make any TV ‘smart’

Q The Raspberry

SAFE VESA

Mount add-on

attaches the

Pi to most

flat-screen TVs

Game on!

Why not turn your smart TV into a

games console?

Q The MOGA

can also

cradle Android

phones, hence

the square

shape

If the buzz around the Ouya is anything to go by, a lot of

people are interested in how to turn Android into a games

console. With a Raspberry Pi running Android, you’re

already part way there. While you could use a mouse and

keyboard for some games, others will probably work better

with a joypad, and this is where the MOGA controller comes

in. It connects via Bluetooth to Android and is able to

control a number of Android games.

Get OnLive

If Android games don’t really do it for you, how about full-

blown PC games? The OnLive streaming service allows you

Smart TV is a very recent and popular buzzword

for a more advanced media PC running inside

your TV, which add a whole host of different apps

as well as being able to stream your content

from around a network. Android itself does not

need any speciﬁ c apps or skinning to turn it into

a functional smart TV – the display is already

conﬁ gured for easy access to all the installed

software, and using home replacement apps

such as Launcher Pro will allow you to increase

the number of on-screen apps if the stock

launcher displays too few for you.

This usage for Android has not gone

unnoticed by other people, with a few

companies already on board. Recently, a high-

proﬁ le Kickstarter project was successfully

funded, called Pocket TV by Inﬁ nitec, which

while deﬁ nitely not the ﬁ rst Android-powered

smart TV device, is notable for running off a USB

stick. Like the Pocket TV, the Raspberry Pi is

capable of running 1080p video without an issue.

The beneﬁ ts of Android even go beyond the TV,

as Ahmad Zahran, founder of Inﬁ nitec, explains:

“[You] get access to all your information,

games, TV streaming channels, work

documents and your entire digital life. You’ll

have all the beneﬁ ts that you get from carrying

your smartphone but with the ability to display

it on a much bigger screen. Imagine walking

into a meeting and doing a presentation

without a laptop.”

As well as having access to simple

information apps such as the Weather and

Stocks, you can also use Android widgets to

add a news feed or social network streams, and

you can even connect to streaming websites

like Netﬂ ix or the BBC iPlayer, as well as

browsing the web.

Once you’ve got your Raspberry Pi set up as an

Android smart TV, you may be wondering where

to put it. Well luckily, there are a few cases out

there that support VESA mounts, the standard

used to attach ﬂ at-screen TVs to brackets and

walls. The Raspberry SAFE case by Solarbotics

is just the tool to tuck it out the way.

to buy and rent games and play them anywhere, thanks to

all the legwork being done in the cloud. Using the OnLive

Android app, you can access these games from your

Android-powered Raspberry Pi and play them directly

on your television without the need for a bulky PC in your

living room. And it also works out much cheaper than the

ofﬁ cial OnLive console.

72 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks, & Hacks 73

Home

automation

In-car computer

Fit a Raspberry Pi in your car

There’s no need for costly

ofﬁ cial controllers

Q Conrad Vassallo has tried a few solutions for

home automation, including some using the Pi

looking up information, such as recipes via the

Epicurious app, or using it to stream music from

your ﬁ le server while you cook.

Home automation controller

Using your Android-powered Pi to control the

house is fairly simple once you have it up and

running. However, you can make it completely

customisable using software like Open Z-Wave

to set up timed events and remote access using

your Raspberry Pi as the controller.

“When I got my ﬁ rst Raspberry Pi, I thought

it would make the project more interesting

to have a dedicated appliance to control my

lights,” explained Conrad Vassallo, who already

had a fully working solution. “So the next step

was to install SSH, Apache, PHP and MySQL

and my code on the Raspberry Pi. Now my

system was consuming very little power and

performed ﬂ awless!”

The system created by Conrad also supports

Android input. “The Raspberry Pi is an excellent

piece of hardware to ‘embed’ systems into. First,

it is very small, silent, green and provides the

services offered by larger, more expensive PCs.”

Using home automation can be fairly simple.

There are a number of different standards used

for achieving it, such as powerline-based X10, or

the RF-controlled Z-Wave products. These are

usually controlled by very expensive remotes and

wall screens, vastly increasing the price over the

hardware you’d need in the ﬁ rst place.

There’s also a problem with running on open

source operating systems. We spoke to an open

source home automator, Conrad Vassallo, about

the problems he faced even getting it started:

“I did some research on systems that provided

home automation and concluded that Z-Wave

was the best option for me… soon I could control

the lights in my living room with the touch of

a button on a remote control. However, this

was not enough: I wanted to have the system

controlled by timed events and so the quest

for a Z-Wave computer interface was on. First I

bought a ControlThink USB stick, which did work

ﬁ ne for my needs; however, my home server runs

on CentOS and the ControlThink USB stick was

only supported under Windows. So I had to run

the system on a virtual machine, which was not

the best option on an Intel Atom PC.”

Luckily he was able to get a setup running using

code from the Open Z-Wave project, creating

his own controller out of it – you can obtain the

source code from here: code.google.com/p/

open-zwave-controller/source/checkout.

The beneﬁ t of running these Z-Wave systems

is that you can control them using Android apps.

A Raspberry Pi and a small screen to connect it to

cost a lot less than the ofﬁ cially made products

and generally work better for the purpose, as you

can always use the extra Android apps on the

device anyway, whether it’s mounted on a wall or

a small box on your coffee table.

Kitchen computer

The size of a Raspberry Pi allows it to ﬁ t in a lot of

spaces – add a touch screen and it takes up very

little room. Putting it in a discreet location like

the corner of a kitchen worktop gives you instant

access to the internet and your home network for

The main issues usually associated with carputers are

ﬁ nding a small enough computer with enough power to do

the tasks you’d want it to do, and then making sure you have

a proper way to actually power the system once it’s in place

in your vehicle. On its own, the Raspberry Pi is a solution to

this problem, with the ability to be powered solely from the

cigarette lighter using a USB adaptor that you’d normally

ﬁ nd for phones.

Running Android on top of that makes it the perfect in-car

computer. In the past, even with a touch screen, navigating

around an operating system was tricky, especially

while on the move. While there have been a lot of recent

improvements to the Linux kernel and X for touch and

multi-touch inputs, the desktop environments themselves

are optimised for mouse and keyboard – at least, the

lightweight ones like LXDE that would run on a carputer.

With Android, that is no longer an issue. As well as a

fantastic selection of apps for music and podcast playback,

you also have the fairly advanced satnav apps like Waze and

even the native Navigation software. To top it off, there’s

also a customisable car dock mode that gives you bigger

buttons and default access to car-friendly apps.

Tips | Tricks | Hacks

The making of Razdroid

What caused you guys to start the project in

the ﬁ rst place?

Viktor Warg: Well, I had just gotten my

Raspberry Pi and instead of just loading up

Debian as suggested, I started browsing the

forums for something more, well, fun, to run

on it. Stumbled upon the Android thread and

knew instantly that I wanted Android on my Pi.

Started collaborating with Mathijs and Les and

one thing led to another, and here we are!

Les de Ridder: The only real reason I was

interested in doing it was because it hadn’t

been done before. I thought it would be really

nice to be part of something like this, as I had

never done any porting or even embedded

projects before.

What limitations did you experience with the

Raspberry Pi?

VW: The main limitation was the lack of open

source libraries for the VideoCore IV (the Pi’s

GPU) which had put the project in somewhat

of a slumber for a few months. This led to the

fact that we had a fully functional Android

system but lacked the appropriate graphics

libraries to make it hardware accelerated

and thus the response times for the UI were

sluggish at best.

LdR: Well, mostly Android compatibility issues.

First of all, support for the Pi’s relatively old

CPU was pretty much broken in the then-

available Android sources; Mathijs luckily

managed to ﬁ x this. Other limitations were

obviously the RAM: with 256MB, Gingerbread

works, but Ice Cream Sandwich runs… well…

much slower to say the least. This is not only

caused by the RAM, but also by the lack of

hardware graphics acceleration. Android

requires people to build custom accelerated

drivers for its libraries (eg Bionic). We couldn’t

do this at the time when we ﬁ rst built ICS for the

Pi and still cannot, because the drivers’ sources

are sadly closed source.

How challenging was it to build Android for

the Raspberry Pi?

VW: It was quite a challenge at ﬁ rst, seeing as

none of us (as far as I know) had been involved

in similar projects at all. As we progressed (or

didn’t, in some cases), things fell into place,

though. Eventually, I’d venture as far as to

saying that all three of us knew what most

of the issues we faced stemmed from and

how to solve them. One issue we had quite

early was that the Raspberry Pi kernel wasn’t

compatible with some of the patches Android

needed, mainly the IPC-Binder that it relies on

heavily. If I recall correctly, that was solved by

our main kernel guy (Mathijs) after a few days

of brainstorming.

Mathijs de Jager: Another issue was a strange

problem with executables crashing all the

time (‘segfaulting’). After some help from

the #cyanogenmod-dev channel, it turned

out to be a bug regarding the ageing ARMv6

Q The team want to get Roku-style

streaming on the Raspberry Pi

Q The Raspberry Pi Foundation’s successful

attempt at running Android on a Raspberry Pi

Razdroid was developed by a small team of like-minded

people, eager to test out the Raspberry Pi’s limits. We

spoke to three members of the team, Viktor Warg, Les

de Ridder and Mathijs de Jager, about their involvement

74 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

architecture in the CyanogenMod sources we

used. Additional build ﬂ ags, almost speciﬁ c to

the Pi, were needed too. This had us stuck for

quite a while.

What project ideas do you guys have for a

ﬁ nished product?

LdR: I personally would like to make a build

that anyone who owns a Pi can use, whether

it’s a Model A with limited peripheral support

or a new fancy Model B with 512MB RAM. This

might mean that we would have to remove some

features, but I think that we will be able to ﬁ nd

a good conﬁ guration that works for the largest

part of the people who are interested in running

Android on their Pi, suiting as many people

as possible. For people who are interested in

making their own builds, we will supply patches

so they can make their own conﬁ guration but

still use our patches for the Pi. I don’t really have

any personal projects, but using it as a Google

TV-like internet player would be nice.

What had you been using the Raspberry Pi for

before Razdroid?

MdJ: Mine had been running as a local web

server for testing.

VW: Nothing at all. I had just gotten my Pi when

I started helping the Razdroid project.

LdR: Not much to be honest. I only had just

received my Pi when I started working on

Razdroid. I was still waiting for my Pi electronics

starter kit to arrive back then, which I later used

for learning some basic electronics, like using

resistors, LEDs, transistors etc.

Any future plans for ports or development on

the Pi?

MdJ: Netﬂ ix on Android on the Pi seems

attractive and I can imagine a lot of people

would want that, but I heard some DRM module

Contribute to Razdroid

Here’s some ways you can help port Android

As Eben Upton said, the Raspberry Pi is about content

creation, and what better way to do this than by getting

in on a project and helping out with the Android port?

Razdroid’s Viktor Warg tells us that the drivers are a

good start, but they need a little more: “We’ve analysed

the libraries and ﬁ gured out that we need to implement

our own userland gralloc-module, and none of us have

even the slightest idea on where to start on that.”

The best place to start is to visit the Razdroid wiki,

www.razdroid.net, and check on the current progress.

There’s also an IRC channel, #razdroid on Freenode,

where the developers regularly talk about their current

work, and the entire project is maintained on GitHub.

Of course you can always start your own project,

either by using the ofﬁ cial Android source from the

AOSP, modding CyanogenMod, or forking Razdroid.

Happy hacking!

is needed. The Broadcom CPU seems to have

it (for example the Roku 2 has Netﬂ ix and

has the same Broadcom CPU), but needs to

have it enabled. Maybe the Pi Foundation can

eventually get a licensing thing going, just like

the MPEG2-decoding licence.

Q Razdroid is

based mainly on

the CyanogenMod

Android firmware

“The Pi kernel wasn’t compatible

with some patches Android needed”

Raspberry Pi Tips, Tricks & Hacks 75

Tips | Tricks | Hacks

76 Raspberry Pi Tips, Tricks & Hacks

Don’t leave your Raspberry Pi behind – incorporate it

into mobile projects by powering it with AA batteries

Add a battery pack

to your Raspberry Pi

Your Raspberry Pi’s mobility is usually restricted by the

length of the power lead. Rather than limiting it to your desk

or living room, however, you can use it for mobile projects as

diverse as launching it into near-Earth orbit or monitoring and

automating your garden.

Of course, to do this you will need batteries, but adding

battery power to your Raspberry Pi is simpler than you might

have imagined. All that is required are six rechargeable AA

batteries (or single-charge alkaline), a battery box with space

for the batteries and a UBEC. The latter is a Universal Battery

Elimination Circuit, a voltage regulator that will regulate the

power supply and prevent damage to the Raspberry Pi, and can

be bought for under £10.

What you’ll need

Q AA battery box

bit.ly/1FDiJGa

Q 3-Amp UBEC

bit.ly/1HLKih7

Q 3-Amp terminal strip

Q 6x AA rechargeable

batteries

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 77

Tips | Tricks | Hacks

01 Order your components

If you’re buying your components online, you should be

able to get them all within ﬁ ve days. However, if you’re ordering

ofﬂ ine (speciﬁ cally the UBEC), you should avoid traditional

electronics stores and instead visit a model enthusiast store, as

these circuits are regularly used in RC devices.

02 Check your UBEC

Two types of UBEC are available. If you used the store

that we suggest in the resources box to the left, you’ll receive one

with a micro USB power connector for easy connection to your

Raspberry Pi. However, if you bought one from eBay then there is

a strong chance that you will receive one with a 3-pin connector.

05 Add a battery to boot

With your Pi ready to use and your Wi-Fi dongle plugged

in, connect the UBEC to the micro USB port and insert the sixth

battery into the battery box. The Pi’s power and status lights

should indicate that the computer is booting up, which gives you

a fully portable computer.

06 Connect the 3-pin UBEC

If you purchased the UBEC with the now-modiﬁ ed 3-pin

connector, you’ll need to connect this to the Raspberry Pi’s GPIO

header. Speciﬁ cally, connect the positive +5V (red) connector to

Pin 2 and the negative 0V connector to Pin 6. Once again, check

the status lights to ensure the Pi is booting.

03 Change the UBEC connector pins

To use the UBEC with a 3-pin connector, alter the

position of the pins so that they occupy the two outer slots.

Use a small jeweller’s screwdriver to lever up the small plastic

catch and remove the red wire from the central slot, before

sliding into the unoccupied outer slot.

04 Connect the UBEC to the battery box

With ﬁ ve batteries in the battery box, connect it to the

UBEC: red-to-red, black-to-black. You might do this by twisting

the wires or soldering, or employ a 3-amp terminal strip, cut

down to two pairs. The terminal strip can be cut to size using

a modelling knife.

Left You can also use

a UBEC to charge

your smartphone

from a battery pack

It is possible

to power your

Raspberry Pi

directly from four

or more batteries,

but without the

safety that the

UBEC provides

you’re likely to burn

out the computer.

Unregulated

power can cause

considerable

damage to your

Raspberry Pi, and

as you increase the

current with more

batteries, the risk

also increases.

Unless you are

planning to learn the

hard way and you

have plenty of cash

to burn, always use

a UBEC!

Use a

UBEC

07 Measure uptime

You should have already set up your Pi for SSH use, so

connect to the device via Putty after giving it time to boot fully (at

least 60 seconds). In the terminal, enter:

watch -n 60 uptime

This command will display the system uptime and also keep the

Wi-Fi connection active.

08 Judge your uptime results

Uptime results depend upon the type of battery you use

and the Raspberry Pi model. Single-charge batteries will last a

little bit longer, but this is a more expensive option. Meanwhile,

newer models have greater power requirements but run for less

time. For more power, add more batteries!

09 Power extreme!

More batteries added in parallel should result in almost

double the uptime (at least 16 hours on a 256MB Raspberry Pi

Model A), but instead of alkaline or rechargeable batteries you

might consider a modern lithium-based AA cell, which will last

considerably longer than alkaline batteries.

Tricks

80 10 Inspiring

Pi Projects

96 Set up the PiTFT touch screen

120 Make a digital photo frame

116 Add gesture control to your Pi

112 Build a network of Raspberry Pi’s

110 Tether your Pi to Android

106 Build a radio transmitter

102 Make a Raspberry Pi sampler

100 Portable Pi video player

98 Calibrate a touch screen interface

78 Raspberry Pi Tips, Tricks & Hacks

• Retro arcade cabinet

• Audiobook reader

• Web radio

• Media caster

• Portable Wi-Fi signal repeater

• Secure Tor web station

• Private cloud storage

• AirPi

• Dusklights

• Outdoor time-lapse camera

106

124 Pygame Zero

120

116

120

“Fire up your imagination

and test your Python skills”

Raspberry Pi Tips, Tricks & Hacks 79

110

80 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

The Raspberry Pi has come a long way over

the last couple of years, and it’s all down to

the creativity and imagination of a burgeoning

community that’s bought over three million of

these single-board computers. They’ve powered

quadcopters and coffee makers, self-sailing boats

and even touched the edge of space, but the one

thing that’s still as much in demand as it was on

launch day is an idea.

Our Raspberry Pi community works so well

because we all share our work with each other. We

can all see what everyone else is up to and, if we see

something that we like, we can have a go at making

it ourselves – and then changing it, so we can share

a different version. It’s all about inspiration.

So for this feature we made ten inspiring

projects for you to try – and we encourage you

to deviate from the steps when a new idea takes

hold and let us know where your project leads

you! There’s a range of different projects here for

you to try, covering media and entertainment,

networks, security and more. All the components

you’ll need for each one are listed on the page –

we’ve tried to keep the cost down as much as

possible by using widely and cheaply available

parts – and each project is simple enough for you

to work through in a single sitting.

One more thing to mention – some of our

Raspberry Pi creations are designed to be

combined, to give you a great starting point when

you begin adapting these projects to the way you

want them. If you come up with any combinations

we’ve missed, be sure to tweet us a photo (we are

@Books_Imagine) – and have fun making them!

Fire up your

imagination

and test your

Python skills

projects

Inspiring Pi

Tips | Tricks | Hacks

88 89

Wi-Fi repeater

Private cloud

Dusklights

AirPi

Time-lapse

camera

Audiobook reader

Secure web station

Web radio

84 85

We are very big fans of retro gaming, and when the Raspberry

Pi was released a couple of years ago we immediately

recognised its potential as an excellent device to power a

homemade, MAME-using arcade machine. Maybe one day we

could use a Raspberry Pi or another Linux-powered machine to

run a cabinet in the future.

We weren’t the only ones that realised how well a Pi would

ﬁ t in an arcade machine; many projects have been completed

since then with impressive results. If you don’t fancy carving out

custom pieces of wood just yet then you can always start small

with the Cupcade kit from Adafruit. The kit is composed of laser-

cut plastic panels, a PiTFT screen and a selection of buttons,

custom boards and a special joystick that can be assembled into

a miniature MAME arcade cabinet.

Unfortunately, for the moment, the Cupcade only supports

the original Model B. However, we like to think of it as a great

excuse to test out whether or not your Model B is up to the task

of powering an arcade machine in case you want to expand. If

not, that means you’ll need another Raspberry Pi to replace the

arcade one, in which case you can always upgrade to a Model B+

or the more recently released Model A+.

When you get the kit in, you’ll need to assemble the

components step-by-step. It’s a long process which we don’t

quite have room for in this issue, so instead we’re going to point

you towards the excellent Adafruit instructions for constructing

your Cupcade: https://learn.adafruit.com/cupcade-raspberry-

pi-micro-mini-arcade-game-cabinet/.

A brief word of warning: it will take you a few hours to

complete, so make sure you have some time clear to do

so. It’s quite ﬁ ddly in places as well, so it might be worth

getting a second pair of hands to help you. When

attaching the side panel to the screen, speaker and

What you’ll need

Q Raspberry Pi Model B

Q Adafruit Cupcade

adafruit.com/product/1783

Q 1.5 A power supply

Q Soldering iron

Q Wire strippers

Q A short length of audio wire

Left It’s a bit tricky to get across the size

of the Cupcade in this picture. Imagine

the joystick is the same size as the

analogue stick on a console controller

Create a tiny arcade machine

and learn how to expand it into

a fully-stocked games cabinet

Retro arcade cabinet

82 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 83

Tips | Tricks | Hacks

The emulators will still

work when you use the

HDMI port to hook it up

to a normal TV

Top lef t You can

always reverse the

button mapping for

traditional NES-

style control

Top right The

Raspberry Pi sits

snugly below a great

bale of wires

Bottom Upgrading

to a full-size

arcade cabinet is

easily done, as the

principles are the

same as with the

Cupcade build

buttons, we suggest ignoring the instruction to carefully lift

the panel off your work desk. Instead, try sliding it slightly off

the desk itself so that you can access each screw one at a time

without having to precariously balance the sections at an angle.

Once completed, it’s time to test it out. Adafruit has a

pre-rolled image you can write to an SD card which can be

downloaded with:

$ wget http://adafruit-download.s3.amazonaws.com/

cupcade-5-13-2014.img.zip

Write it to a 4 GB card (your Cupcade comes with one),

download the free, non-commercial ROMs they provide to

test the setup and power it up with a proper plug adapter. The

components are running directly off the Pi and can be quite

power-hungry, so it’s imperative that you properly power it.

The image we’ve written has a full MAME arcade emulator

in it, and a NES emulator. They’re both conﬁ gured to use the

buttons you’ve installed on the case by default; this means that

because the NES emulator directly maps the cabinet’s A and B

buttons to its own A and B, the layout is the reverse of the NES

controller, which had A on the right and B on the left. Depending

on what you plan to use the cabinet for, you can either

swap over the buttons or just get used to a slightly altered

control scheme.

How can we expand the Raspberry Pi from here to create a

full-sized cabinet? The good news is that the emulators will still

work when you use the HDMI port for output instead, allowing

you to hook it up to a normal TV. The buttons and speakers

will still work as well and they can be plugged straight into the

Raspberry Pi’s GPIO port via a connecting ribbon, like we used

with the board to the screen.

However, this does leave you with only four buttons and the

small joystick; luckily there are plenty of USB arcade sticks

and components out there that can be connected via USB,

and with the right conﬁ guring you can get them working on the

emulators just ﬁ ne.

There’s a lot more you can do with the Pi once you’ve got it

set up in a cabinet, such as letting it connect to the network

so you can remotely maintain it without having to disassemble

the entire thing to retrieve an SD card. Make sure you do your

research on speciﬁ c parts and look out for any community

forums that will deﬁ nitely have helpful advice on what to buy.

One of the best

arcade cabinet

projects we’ve seen

has been featured on

the Raspberry Pi blog:

bit.ly/1pWjQWE

Using an old arcade

cabinet for parts,

the maker managed

to modify the inputs

to be read by the Pi

and got the coin slot

to work. You don’t

need to go this far

by getting a CRT

monitor or even an old

busted cabinet, but it

certainly adds a ﬂ air

of authenticity to a

project like this.

inspired

84 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

Create an audiobook player that works at

the touch of a button

Audiobook reader

Audiobooks and podcasts are

becoming more and more prevalent in

a society where we’ve learned to multi-

task thanks to all our modern devices.

Whether out and about or doing some

chores, it can be nice to have some extra

sensory input when you’re not using your

full concentration. Enter, like always, the

Raspberry Pi. With only a small selection

of components and a pair of earphones

or portable speakers, you can take your

Raspberry Pi with you and have it play

audio books.

First, you need to get the Raspberry Pi

ready. Do your usual apt-get update and

apt-get upgrade in the terminal before

you start, although there isn’t really much

What you’ll need

Q Speakers

Q LED

Q 1.2 k resistor

Q 10 k resistor

Q Push-button switch

Q Breadboard and wires

Right The synergy

between these two

projects means you

can use the same

setup for both

Below This circuit

will work on both the

Model B and Model

B+ – the pins begin

at the same end of

each board

preparation involved. Once that’s done, all we need to do is install

VLC, which is done with:

$ sudo apt-get install vlc

Once that’s done, turn off your Pi, disconnect the power and

begin hooking up your circuit as according to the Fritzing

diagram below. It’s a fairly simple setup – we’re going to use

the button to activate the playing of the audiobook and the

LED will turn on while this is happening.

Once you’re conﬁ dent with the circuit, turn your Raspberry

Pi back on and open up the terminal. Type in the following to

download the Python code for this project:

$ wget http://www.linuxuser.co.uk/wp-

content/uploads/2014/08/audiobook.zip

There are a couple things we need to note about the code:

it ﬁ rst of all assumes you have your audiobook located in a

directory known as audiobook within your home folder. It also

looks for a ﬁ le called audiobook.mp3 to play; you can easily

change this by editing the path but you’ll need to be consistent

with the name of the ﬁ le you have on your Pi. You could always

have it point to a speciﬁ c location on a USB stick, swapping

out the ﬁ les on another computer and renaming them

appropriately once you’ve ﬁ nished with previous book.

Test it out by running the code – one press of the button

will start the process while another press will stop playing the

book. If you ﬁ nd the button press too sensitive or not sensitive

enough, edit the delay in time.sleep which is currently set at a

default of 0.2 seconds.

Raspberry Pi Tips, Tricks & Hacks 85

You can easily

put both projects

together and have

an all-in-one radio

and audiobook. Wire

up a second button

that will play the

audio book instead

and maybe even

add extra buttons if

you like for different

radio stations.

Put ’em

together

on command. Double check all your connections on the

breadboard and then plug your Pi back in.

Open the terminal and use it to download our Python script

for playing internet radio:

$ wget http://www.linuxuser.co.uk/wp-content/

uploads/2014/08/webradio.zip

Unzip the ﬁ le and put it wherever you want; it doesn’t require

any special placement in your Pi’s ﬁ le structure. You will likely

want to change the radio station that the code is currently

tuned to, and this can be found in the subprocess.Popen line

in the code. Find an m3u URL for your favourite radio station

and replace the URL already in that code to get it to play.

There may be a short delay between pressing the button

and the music starting as VLC launches and gets the stream

buffered. We’ve made it so the light comes on straight away,

though, so at least you’ll know the process has started.

Pressing the button again will kill VLC and stop the radio

stream. If you feel the button is too sensitive or not sensitive

enough, look for the time.delay setting and change the

amount of time it requires the button to be pressed.

Our Raspberry Pi web radio is a true companion piece to

the audiobook over the page, and we’ll get into why as we

go through this tutorial. Like the audiobook, we’re taking full

advantage of the Raspberry Pi to help aid you in a real-life

situation. As standard radio methods begin to die out, the

established web-streaming platforms will become more and

more popular, and you can get in on those straight away using

this project. The circuit for this is also the exact same one as

the audiobook, so if you’ve already had a crack at that, then

you’ll just need to grab the code for this tutorial.

Before you wire it up, it’s time to prepare your Raspberry

Pi. Open the terminal and do an apt-get update and apt-get

upgrade to make sure everything is up to date, followed up by

installing VLC using:

$ sudo apt-get install vlc

When it’s ﬁ nished installing, you will need to turn off

your Raspberry Pi. Disconnect the USB cable, break out

the breadboard and components and follow the wiring

diagram. It’s not a complicated circuit at all, and revolves

around sensing a button being pressed and lighting an LED

A portable radio that streams web content wherever you are

Web radio

86 Raspberry Pi Tips, Tricks & Hacks

Have you ever wanted to move between

rooms while watching or listening to

the same film or song? We often ﬁ nd

ourselves switching from a phone or

tablet to the desktop. There are some

complicated setups you can use for this

involving MythTV and various custom-

built servers and receivers, but you can

also do it with just one Raspberry Pi

server and then many XBMC receivers

with a lot less hassle.

Broadcasting your media over your

network so that the clients can pick up

the stream means that you can easily

pick up where you left off in your track

or ﬁ lm wherever you move to, without

having to make a note of the track

position and ﬁ nd the ﬁ le again. Here’s

how to get set up.

What you’ll need

Q Raspberry Pi Model B

Q XBMC

http://xbmc.org

Q Portable hard drive

Cast your content over the local network to receive it

from multiple clients so you don’t lose your place

Media caster

01Install storage drivers

You’ll likely be using a portable NTFS hard drive if you

want to store a lot of media on your Raspberry Pi caster. This

means you need to install the NTFS libraries on the Pi, which

requires you to open the terminal and type:

$ sudo apt-get install ntfs-3g

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 87

Tips | Tricks | Hacks

SSH into your Pi from

another computer or an

Android device

Left Media stored on

your portable hard

drive will show up in

a dedicated folder

Why not add a web

interface to your Pi so

that you can browse

from your laptop or

smartphone? Have

it run the multicast

code when clicking

on ﬁ les it’s scraped

from the media drive

to make the process

much easier. You can

also fuse the project

with our cloud server

in a few pages time.

inspired

02 Create mounting folder

We’re going to have the Raspberry Pi automatically

mount the hard drive for us whenever it boots up, and in order

to do this it ﬁ rst needs to have a place where the ﬁ les will be

accessible. Let’s create a directory called mediadrive inside

the Home folder. Keep the directory name to just one word to

make your life easier later.

$ mkdir mediadrive

03 Boot-time mount parameters

Your hard drive will likely be mounted as /dev/sda1, but

do a fdisk -l if you want to double check. To make sure it mounts

at boot, go to fstab with sudo nano /etc/fstab and write the

following line below, with a tab between each bit of information:

/dev/sda1 /home/pi/mediadrive ntfs-3g

defaults,noatime 0 0

04 Install VLC on Pi

So all our media is now accessible, and now we need

a way to broadcast it. For this we’ll use multi-functional media

player VLC, which was originally designed to be the client for a

casting server. You can install it with:

$ sudo apt-get install vlc

05 XBMC stream receiver

This bit is dead simple – on any computer you can

easily get ﬁ les off of, create a ﬁ le called Stream.strm, and add

this line to it, with IP as the last two sets of Pi’s IP address:

udp://239.255.[IP].[IP]:1234

Save it and move it to your XBMC clients that you want to

receive the cast from.

06 Custom VLC command

Here’s the really fun part. Go back to your Pi and right

click on one of the ﬁ les you’d like to play, go to Properties and

click the down arrow next to Open with. Go to Customise and

then Custom Command Line and type in the following, with IP

as the last two sets on your IP address:

cvlc --sout udp:239.255.[IP].[IP] %f

07 Test out casting

Here’s the big test: boot up XBMC, open your media on

the Raspberry Pi and use the Stream ﬁ le on XBMC to receive

the cast. It might take a moment to load but it will start

playing via XBMC in short time.

08 Command line alternative

Your setup may not always be convenient for you to go

to the Pi and start launching ﬁ les from the desktop. You can

always SSH into your Pi from another computer or an Android

device and run the ﬁ le using a similar custom command to the

one we used earlier:

$ cvlc --sout udp:239.255.[IP].[IP] [file location]

Tips | Tricks | Hacks

Boost your signal using a Raspberry Pi and two USB Wi-Fi dongles

Portable Wi-Fi

signal repeater

What we like about the Raspberry Pi for this

project is that it’s very low maintenance and

extremely easy to put in an appropriate location.

All you need for this project are two USB wireless

adaptors, a nice little case and a way to power it.

Once you’ve set it up, you can basically leave it to its

own devices, checking in over SSH every now and

then to do some updates.

Set this up on a monitor with a keyboard, using

a fresh image of Raspbian and with your Wi-Fi

dongles plugged in. On ﬁ rst boot keep it as CLI and

after doing the usual apt-get updates and upgrades,

type startx to get to the desktop. Conﬁ gure the

wireless for wlan0 to connect to your home network

and make sure it has a ﬁ xed IP address, then reboot

to make sure it all works from the command line by

using ping www.google.com. Now you need to install

your ﬁ rst bit of software using:

$ sudo apt-get install hostapd iw

After it’s installed, you’ll want to download and save

the ﬁ le we’ve created directly to conﬁ g by entering

the following two commands:

What you’ll need

Q 2 USB Wi-Fi adaptors

Q Raspberry Pi case

Q Portable power pack

Right One Wi-Fi adaptor picks up

your main Wi-Fi network, while the

other one broadcasts a new signal

88 Raspberry Pi Tips, Tricks & Hacks

Raspberry Pi Tips, Tricks & Hacks 89

Tips | Tricks | Hacks

Stay private online by routing all

your web trafﬁ c through Tor on

your Raspberry Pi

Secure Tor

web station

Right Adafruit’s Onion Pi Pack

contains all the components you

need to set up a secure connection

Above As well as from the main Tor website, you can also download Tor

from this issue’s DVD

A secure wireless

connection can be

created using the

Raspberry Pi by

looking at the Onion Pi

project from Adafruit:

learn.adafruit.com/

onion-pi/overview

This creates a

wireless access

point connected

to the internet that

anonymises all web

trafﬁ c by directing it

through the

Tor network.

This means all your

home computers and

smart devices can be

connected to Tor and

not just the Raspberry

Pi itself. You can

also apply some of

the lessons learnt in

the Wi-Fi repeater

tutorial to unshackle

it from the ethernet

cable, although that

will reduce slightly its

overall security.

Put ’em

together

In a much more privacy-focused world, being able to

browse securely online is an important freedom for many

people. With the use of Tor and a few tweaks to the Raspberry

Pi, you can make sure all your internet trafﬁ c is kept private.

First of all, you’ll need to make sure to install Tor from the

repos. Open up the LXTerminal and simply type:

$ sudo apt-get install tor

Once that’s done, edit the torrc ﬁ le by using sudo nano /etc/

tor/torrc and add this to the top of the ﬁ le:

VirtualAddrNetworkIPv4 10.192.0.0/10

AutomapHostsOnResolve 1

TransPort 9040

DNSPort 53

Save this and then open the next ﬁ le with sudo nano /etc/

resolv.conf ﬁ le and modify it:

na meserver 127.0.0.1

Finally, you need to change the iptables ruleset, but before

you do this, use top to conﬁ rm the uid of Tor and make a note

of it. Now open up a new ﬁ le with nano /etc/init.d/iptables and

enter the code found at: http://www.linuxuser.co.uk/wp-

content/uploads/2014/08/tor.zip. Now save it and enter:

$ chmod 755 /etc/init.d/iptables

$ update-rc.d iptables defaults 12

$ wget http://www.linuxuser.co.uk/wp-

content/uploads/2014/08/repeater.zip

$ cp LUDRepeater.conf /etc/hostapd/hostapd.conf

Do a reboot and test the conﬁ guration ﬁ le with:

$ hostapd -dd /etc/hostapd/hostapd.conf

If there are no errors, open the ﬁ le using nano /etc/hostapd/

hostapd.conf and then add the following to the ﬁ le:

DAEMON_CONF=“/etc/hostapd/hostapd.conf”

RUN_DAEMON=yes

Also change the SSID to be the same one for your network in

the ssid ﬁ eld. Once that’s done, you’ll need to install the bridge

utilities with apt-get install bridge-utils. Then conﬁ gure it with

the following four commands:

brctl addbr bridge0

brctl addif bridge0 wlan0

brctl addif bridge0 wlan1

ifconfig bridge0 up

Test it out to make sure it works and then place it around

the house to extend your wireless signal!

Tips | Tricks | Hacks

The themes of a lot of our Raspberry Pi guides revolve

around the size and portability of the Pi itself, lending

it to tasks you may have used a full-sized or small

computer for in the past that the Pi can now take over.

Having your own private cloud is another excellent use of

the Raspberry Pi’s capabilities, because you can store it

hidden away somewhere and it will require very little day-

to-day maintenance.

Make sure you invest in some decent, portable USB

storage such as an external HDD, and also get a case for

your Pi in the process.

What you’ll need

Q External storage

Q Constant internet

connection

Left Rather than store all your

media and ﬁ les on a cloud server

in an unknown location, you can

keep a cloud in your own home

Turn the Pi into your own personal

Dropbox using ownCloud and an

internet connection

Private cloud storage

01Set a static IP

After setting up your wired or wireless internet

connection, you need to make it static. Use sudo

nano /etc/network/interfaces to open up the network

settings ﬁ le. Fine the iface eth0 line so you can change

and add to it:

iface eth0 inet static

address 192.168.0.50

gateway 192.168.0.1

netmask 255.255.255.0

network 192.168.0.0

broadcast 192.168.0.255

90 Raspberry Pi Tips, Tricks & Hacks

Raspberry Pi Tips, Tricks & Hacks 91

Tips | Tricks | Hacks

Need an idea of

what your next step

could be? Check out

our media caster

tutorial and maybe

you can fuse the two

concepts together.

Upload videos to

your cloud and get

them to play over

your network.

inspired

02 Install a lot of software

You’ll want Apache software and PHP for this. Install

everything you need with:

$ sudo apt-get install apache2 php5 php5-json php5-gd

php5-sqlite curl libcurl3 libcurl4-openssl-dev php5-

curl php5-gd php5-cgi php-pear php5-dev build-

essential libpcre3-dev libapache2-mod-php5 php-apc

03 Set up PHP accelerator

Install your accelerator with sudo pecl install apc and

create an ini ﬁ le for it. To do this, use sudo nano /etc/php5/cgi/

conf.d/apc.ini and then add this to the ﬁ le:

extension=apc.so

apc.enabled=1

apc.shm_size=30

04 Conﬁ gure ﬁ le limits

Go into the Apache conﬁ g ﬁ le with sudo nano /etc/

php5/apache2/php.ini. It’s a big ﬁ le, but there are two ﬁ lesize

options you need to ﬁ nd, and a third extension option you

need to add as below:

upload_max_filesize = 2048M

post_max_size = 2200M

extension = apc.so

05 Set up SSL

First of all, you need to enable SSL in Apache; do this

by using sudo nano /etc/apache2/sites-enabled/000-default

and change ‘None’ to ‘All’ in the AllowOverride option. Follow

this up with the following two commands:

$ sudo a2enmod rewrite

$ sudo a2enmod headers

06 Finish up with Apache

You now need to do two sets of commands: a big one

which requires some info and then a restart:

$ sudo openssl genrsa -des3 -out server.key 1024

$ sudo openssl rsa -in server.key -out server.key.

insecure

$ sudo openssl req -new -key server.key -out server.csr

$ sudo openssl x509 -req -days 365 -in server.csr

-signkey server.key -out server.crt

$ sudo cp server.crt /etc/ssl/certs;sudo cp server.key

/etc/ssl/private;sudo a2enmod ssl

$ sudo a2ensite default-ssl

$ sudo service apache2 restart

07 Download and install ownCloud

Here you have a series of commands to run that will

download, unzip and install ownCloud to the right place:

$ wget https://download.owncloud.org/community/

owncloud-7.0.0.tar.bz2

$ sudo tar -xjf owncloud-7.0.0.tar.bz2

$ sudo cp -r owncloud /var/www

08 ownCloud permissions

Make sure your hard drive is connected and mounted as

you want it. First, give webserver permission to use ownCloud:

$ sudo chown -R www-data:www-data /var/www/owncloud/

Next, use sudo nano /var/www/owncloud/.htaccess and make

the same changes you did in the php.ini ﬁ le above. Finally, give

permissions to the location you mounted the hard drive to with:

$ sudo chown -R www-data:www-data [mount]

09 Set up ownCloud

Open Midori and navigate to https://[ipaddress]/

owncloud to begin the ownCloud setup process. The ﬁ rst thing

you’ll need to do is change the data location to the mount point of

your external drive, which can be found in the advanced options.

And you’re done!

Tips | Tricks | Hacks

Predict the weather using your own sensor station

AirPi

The AirPi has a pedigree that aligns perfectly with the

mission of the Raspberry Pi Foundation. Created by two

teens in sixth form to measure various forms of pollution, the

project’s popularity exploded with thanks to some highlighting

by the Raspberry Pi Foundation and it’s now the premier way to

create a weather station on the Raspberry Pi.

The AirPi kit comes with a small selection of sensors by

default that can be upgraded and improved upon with extra

breakout boards and modules. Included with the kit is a

barometric pressure sensor, a humidity and temperature

sensor, an ultraviolet radiation sensor and a microphone for

noise pollution.

The ﬁ rst thing you’ll need to do is assemble the kit, for which

you’ll require a soldering iron and a steady hand. There are

some basic instructions that come with the kit you can follow

but it doesn’t hurt to have a look at some of the online images

to ﬁ gure out exactly where everything goes. Be careful when

soldering all the resistors to make sure you don’t melt the 26-

pin connector on the underside otherwise it won’t go on your Pi.

Once that’s done you need to start setting up your Raspberry

Pi. Open up a terminal and get some of the Python tools you’ll

need to use:

$ sudo apt-get install git-core python-dev

python-pip python-smbus

Download and install the python-eeml package:

$ sudo apt-get install libxml2-dev libxslt1-dev

python-lxml

$ git clone https://github.com/petervizi/

python-eeml.git

$ cd python-eeml

$ sudo python setup.py install

You need to install i2c support for the pressure sensor, so ﬁ rst

use sudo nano /etc/modprobe.d/raspi-blacklist.conf and

remove the comment from the blacklist i2c-bcm2708 line.

What you’ll need

Q AirPi

tindie.com/products/tmhrtly/airpi-kit/

Q Soldering iron

Q Solder

Top right Measure your surroundings

with AirPi and share your data with the

scientiﬁ c community

Bottom right The AirPi perfectly ﬁ ts the

Raspberry Pi, so you can easily enclose

your device in a small weatherproof box

Next, open up the modules ﬁ le with sudo nano /etc/modules

and add i2c-dev to the bottom of the ﬁ le. Save that and install:

$ sudo apt-get install i2c-tools

Add your Pi to the i2c user group with:

$ sudo adduser pi i2c

Now reboot your Raspberry Pi before continuing. Finally, install

the ﬁ nal Python module with:

$ sudo apt-get install python-smbus

Now we can install the AirPi code. Still in the terminal, use:

$ git clone -b non-modular https://github.com/

tomhartley/AirPi.git

If you’re using a revision 2 Model B or a B+, use sudo nano AirPi/

AirPi.cfg to edit the conﬁ g ﬁ le. Change I2CBus = 0 to I2CBus

= 1 and alter the next line to read LCD = False. Create a Xively

account, add the API and ID keys to the conﬁ g ﬁ le and save it.

You can now start taking measurements by running Upload.py.

92 Raspberry Pi Tips, Tricks & Hacks

Use your Raspberry Pi to control outdoor lights

that automatically come on when it’s dark

Dusklights

You’ve probably all seen those cheap, solar-powered lamps

that you can stick into your garden to try and give it a classy

bit of illumination during the night. If you’ve actually got

one then you may have found out that they don’t shine very

brightly and the plastic stakes can be very ﬂ imsy. So why not

make your own version? What we’ll show you on this page is

the beginning of an array of light-sensitive LEDs using a single

LED, so that you can understand how the system works. We’ll

use a special resistor called a light dependant resistor (LDR)

or photoresistor that changes its resistance based on the

levels of light it’s receiving.

There’s no extra software you’ll need for this, so just make

sure your Pi is up to date with an apt-get update and apt-get

upgrade. Turn it off, unplug it from the power source and get

to work wiring up the circuit as shown in the Fritzing diagram.

Take special note of the placement of the components,

especially the LDR and the capacitor. What you’ll need to do

is measure the time it takes for the capacitor to fully charge

between pin three of the GPIO ports and ground. Also, make

sure the negative end of the capacitor is hooked to the ground

side of the circuit.

Once that’s done, turn your Raspberry Pi back on and

download the code we’ve created for this project using:

$ wget http://www.linuxuser.co.uk/wp-content/

uploads/2014/08/dusklight.zip

What you’ll need

Q 1.2 k resistor

Q 2.2 k resistor

Q Light dependent resistor

Q 1 µF capacitor

Q Breadboard and wires

Linking up the AirPi

with your dusklights

allows you to have

the ultimate outdoor

Raspberry Pi device,

allowing you to

predict the weather

and control your

outdoor lighting

with more precision.

The humidity and

pressure sensors will

be able to tell if it’s

foggy or not, giving

you more control

over when your lights

turn on.

Put ’em

together

Unzip it and run it. We’ve made it so the Python shell will print

out the values that the circuit returns, with a higher number

meaning it’s darker and the capacitor takes longer to charge.

See how the circuits react to you covering the LDR with a

ﬁ nger or shining a torch on it in order to get an idea of how your

version will work.

To get this working for outdoor use it will require a bit of trial

and error. The easiest way is to set it up when it’s getting to

about the level of darkness you’d want the light to turn on and

record the output from the sensor. Change the if statement so

that it activates the LED over a certain number and you’ll be

set. With some external power and more LEDs you can have

a Raspberry Pi power an entire array of shining lights around

your garden.

Tips | Tricks | Hacks

Raspberry Pi Tips, Trick & Hacks 93

94 Raspberry Pi Tips, Tricks & Hacks

We love the Raspberry Pi camera. It’s a lovely

little piece of kit that is as versatile as the Pi and

it doesn’t even take up any of the USB slots. We’ve

done a bit of time-lapse photography in the past but

that was using a proper camera attached to the Pi –

now we’re doing it with just the Pi camera and a lot

less code thanks to the picamera Python module.

We need to set up our Pi with a few things before

we start with the code, though. We’ll start off with

assuming you’ve got a freshly installed Raspbian

SD card, so the ﬁ rst thing to do is an apt-get update

followed by an apt-get upgrade to make sure your

ﬁ les are up to date. Follow this with an rpi-update to

make sure your ﬁ rmware is also up to date – this step

is very important because if you’re using an outdated

ﬁ rmware then the camera won’t work.

The next step is to get the camera enabled. Open

up the terminal if you’re on the desktop, or simply

write into the command line:

$ sudo raspi-config

Find the Enable Camera option. Press Enter and key

over to Enable. Go to Finish but don’t restart straight

away as you have some more commands to get

through. Install your picamera module using this:

$ sudo apt-get install python-picamera

You also need to install the software that you’re

going to use for compiling your images into the

ﬁ nished time-lapse video. We’re using gstreamer

to compile the video as it works well with the

Raspberry Pi GPU. To get it installed, ﬁ rst add the

repo to the sources list with:

$ sudo sh -c ‘echo deb http://vontaene.

de/raspbian-updates/ . main >> /etc/apt/

sources.list’

What you’ll need

Q Pi camera module

Q A weatherproof case, such

as a PICE+

Get beautiful views of the sunset using your

Raspberry Pi, a Pi camera and a small Python script

Outdoor

time-lapse camera

Raspberry Pi Tips, Tricks & Hacks 95

Tips | Tricks | Hacks

Left Ground yourself

and carefully insert

your Pi camera while

the Raspberry Pi

is unplugged

Below The PICE+

case is currently

being Kickstarted,

so it wasn’t available

at the time of

writing, but look out

for it by the end of

the year

With some

modiﬁ cations to

the code and the Pi,

you can make it a lot

more automated,

running the Python

script after boot and

uploading it to the

cloud storage we set

up earlier. You can

also use it as a CCTV

camera thanks to an

additional hood that

comes with the PICE

inspired

Do an apt-get update and then install a huge selection of

packages with the following:

$ sudo apt-get install libgstreamer1.0-0 liborc-0.4-0

gir1.2-gst-plugins-base-1.0 gir1.2-gstreamer-1.0

gstreamer1.0-alsa gstreamer1.0-omx gstreamer1.0-

plugins-bad gstreamer1.0-plugins-base gstreamer1.0-

plugins-base-apps gstreamer1.0-plugins-good

gstreamer1.0-plugins-ugly gstreamer1.0-pulseaudio

gstreamer1.0-tools gstreamer1.0-x libgstreamer-

plugins-bad1.0-0 libgstreamer-plugins-base1.0-0.

Once that’s done, shut down the Raspberry Pi. Unplug the USB

cable and locate the special DSI port for the camera, next to

the HDMI port. Gently pull on the edges to lift the fastener and

slot in your Raspberry Pi camera ribbon – make sure the silver

connectors are facing the HDMI port. Turn your Raspberry Pi

back on and get back into Raspbian. Everything should be about

ready now, so give the camera a test by opening up the terminal

and using:

$ raspistill -o test.jpeg

It will show the preview screen and then take a photo after ﬁ ve

seconds; if it does so, you’re ready to get set up with our code.

Our preferred method for doing this is to ﬁ rst create a folder

called timelapse in your home directory; you can do this simply

by opening the terminal and typing:

$ mkdir timelapse

If you haven’t made any changes to your username and such,

this should create the directory with the full path /home/pi/

timelapse. Keep this in mind and we’ll explain its importance in

a bit. Now in the terminal we’ll download the Python code we’ve

created for this project:

$ wget http://www.linuxuser.co.uk/wp-content/

uploads/2014/08/timelapse.zip

Unzip it and have a quick look through it using IDLE. There are a

couple of things to note in the code in case you wish to modify

it. The photos variable is set to 500 and that’s the number of

shots it will take before compiling the video. In reality it will

actually do one more due to the mathematical quirks of Python

but that shouldn’t matter. The delay parameter is in seconds

and using a bit of Google Fu you can ﬁ gure out that 500 shots

at 30-second intervals will take about four hours to complete.

The large subprocess.call line is used to compile the images

into an AVI ﬁ le at 24 frames per second. It uses the full path

to the directory that we mentioned previously, so if yours is

slightly different make sure you change it now.

There are a number of ways you can use it to get a time-

lapse of the outdoors; the easiest and safest way is to locate

a window with the view you wish to use. This may not always

be easy, though, in which case we suggest trying out the

PICE or PICE+ case. It’s a durable and waterproof case that is

designed to house the Pi and a Pi camera. Once it’s in place,

all you’ll need to do is hook it up to power, preferably with a

long cable, and run the code. Once it’s ﬁ nished, retrieve the Pi

and the AVI ﬁ le.

Tips | Tricks | Hacks

This simple little touch screen takes a bit more

than just plugging it in, as we show in the ﬁ rst of

our hand-held Raspberry Pi video player tutorials

Set up the PiTFT

touch screen

We’ve spoken a lot about about how

portable the Raspberry Pi is, but one

of the minor issues associated with

this portability is the lack of a display.

Carrying around a monitor is hardly

practical and connecting via a phone with

SSH takes some interesting trickery to get

right. The PiTFT screen removes all these

issues by requiring no extra power and

being the size of the Raspberry Pi itself.

While Adafruit does supply a

preconﬁ gured Raspbian image for the

screen, you’ll need to add some extras

to get it working on your current install,

which is exactly what we’re going to cover

in this tutorial.

01Adafruit kernel ﬁ les

The ﬁ rst thing we need to do is download and install the

necessary kernel ﬁ les. Open up a terminal or SSH in and do

the following:

$ wget http://adafruit-download.s3.amazonaws.com/

libraspberrypi-bin-adafruit.deb

$ wget http://adafruit-download.s3.amazonaws.com/

libraspberrypi-dev-adafruit.deb

$ wget http://adafruit-download.s3.amazonaws.com/

libraspberrypi-doc-adafruit.deb

$ wget http://adafruit-download.s3.amazonaws.com/

libraspberrypi0-adafruit.deb

$ wget http://adafruit-download.s3.amazonaws.com/

raspberrypi-bootloader-adafruit-112613.deb

$ sudo dpkg -i -B *.deb

What you’ll need

Q SD card with up-to-date

version of Raspbian

Q PiTFT, fully assembled

bit.ly/1jHEJT4

96 Raspberry Pi Tips, Tricks, & Hacks

Raspberry Pi Tips, Tricks, & Hacks 97

Tips | Tricks | Hacks

02Attach the screen

If you’re using Raspbian from an image after

September 2013, turn off the accelerated framebuffer using:

$ sudo mv /usr/share/X11/xorg.conf.d/99-fbturbo.conf ~

After that’s done, shut down the Raspberry Pi completely

and plug the screen into the GPIO pins if you haven’t already

done so.

03 Install the screen driver

We can do a test to make sure that the screen works

at this point. This will turn on the screen but it won’t work

after reboot:

$sudo modprobe spi-bcm2708

$sudo modprobe fbtft_device name=adafruitts rotate=90

$export FRAMEBUFFER=/dev/fb1

$startx

04 Add the modules

There are two modules we need to get to auto-load

at boot time, including the actual PiTFT driver. Open up the

modules ﬁ le with the ﬁ rst command and add the second two

lines to the list:

$ sudo nano /etc/modules

spi-bcm2708

fbtft_device

05 Edit conﬁ guration ﬁ les

We need to create/modify the necessary

conﬁ guration ﬁ le so that the screen can turn on properly.

The ﬁ rst line opens the ﬁ le, while the second line needs to be

added to this ﬁ le:

$ sudo nano /etc/modprobe.d/adafruit.conf

options fbtft_device name=adafruitts rotate=90

frequency=32000000

06 The options

You may have noticed the speciﬁ c wording on these

options: rotate allows you to have it at 0, 90, 180 or 270 degrees.

A frequency of 32MHz gives you about 20fps on screen; but if the

screen is playing up, take it down to 16MHz. Now reboot the Pi.

07 Install touch screen

Once back in, we need to create a new conﬁ g ﬁ le and

populate it as shown below:

$ sudo mkdir /etc/X11/xorg.conf.d

$ sudo nano /etc/X11/xorg.conf.d/99-calibration.conf

Section "InputClass"

Identifier "calibration"

MatchProduct "stmpe-ts"

Option "Calibration" "3800 200 200 3800"

Option "SwapAxes" "1"

EndSection

08 Testing touch

Once that's all done you can restart X with:

$ FRAMEBUFFER=/dev/fb1 startx

You can make it so you just need to type startx by adding the

following to ~/.proﬁ le:

export FRAMEBUFFER=/dev/fb1

You can also go into raspi-conﬁ g to have the desktop load by

default. That’s it – you’re now ready to start calibrating the

display for your portable video player.

Left Get the

neccessary ﬁ les

from the Adafruit

website and

download them to

your Pi

Calibrate your new touch screen and

add a small interface using some

simple Python code

Calibrate a touch

screen interface

We’ve got a screen with basic touch

functionality but where do we go from

there? Our ﬁ rst step is to actually make

the touch screen usable; it’s resistant-

style touch, so you can use your ﬁ nger

or a stylus with it, and this will affect the

calibration of the screen once we get to

it. Don’t worry – if you calibrate with one

method, you can always go back and

recalibrate with another.

Once you’ve completed the tutorial on

the previous two pages, be sure to give

this one a try. Here we’re going to properly

set up the touch screen so you can

continue to use the Raspberry Pi on the go

without any other devices or within range

of a decent power socket.

01New rules

To make things easier for ourselves we’re going to

create a little rule so that we don’t lose track of what the

touch screen is called in the command line. SSH in, run the

next command and copy the following text into it:

$ sudo nano /etc/udev/rules.d/95-stmpe.rules

SUBSYSTEM=="input", ATTRS{name}=="stmpe-

ts", ENV{DEVNAME}=="*event*", SYMLINK+="input/

touchscreen"

02Reinstall the touch screen

We’ll need to undo what we did at the end of the last

tutorial to make sure we can get the touch part working

properly, by removing and then reinstalling the support for it:

sudo rmmod stmpe_ts; sudo modprobe stmpe_ts

What you’ll need

Q SD card with up-to-date

version of Raspbian

Q PiTFT, fully assembled

bit.ly/1jHEJT4

98 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

Raspberry Pi Tips, Trick & Hacks 99

03 Main event

Find out what event the touch screen is known by

with the following:

$ ls -l /dev/input/touchscreen

We can install tools now to calibrate and debug the touch

screen. Install and test them with:

$ sudo apt-get install evtest tslib libts-bin

$ sudo evtest /dev/input/touchscreen

04 Touch calibration

Now we can ﬁ nally begin the calibration process.

Enter the following so that the Pi can learn roughly where the

positions are on the screen:

$ sudo TSLIB_FBDEVICE=/dev/fb1 TSLIB_TSDEVICE=/dev/

input/touchscreen ts_calibrate

05 Draw calibration

Once you’ve done the previous calibration, you can try

out a drawing test to see how the screen reacts. Do this with

the following:

$ sudo TSLIB_FBDEVICE=/dev/fb1 TSLIB_TSDEVICE=/

dev/input/touchscreen ts_test

If it’s not working quite to your liking, you can try the previous

step again.

06 Install X calibrator

Now we need to calibrate the touch screen in X, which

ﬁ rst means installing the correct tools. Use the following two

commands to download and install the tool:

$ wget http://adafruit-download.s3.amazonaws.com/

xinput-calibrator_0.7.5-1_armhf.deb

$ sudo dpkg -i -B xinput-calibrator_0.7.5-1_armhf.deb

Follow this up quickly by deleting irrelevant calibration data with

the following:

$ sudo rm /etc/X11/xorg.conf.d/99-calibration.conf

07 X-calibrate

From your SSH shell, run startx for the screen to turn

on. From here you can either try to get xinput_calibrator typed

into the terminal or type the following from the SSH session if

it’s easier:

FRAMEBUFFER=/dev/fb1 startx & DISPLAY=:0.0 xinput_

calibrator

08 Save calibration

Having completed calibration, you’ll get an output

starting with Section “InputClass”. Open up the following ﬁ le

and copy the output from Section to EndSection into there:

$ sudo nano /etc/X11/xorg.conf.d/99-calibration.conf

09 Play around

Your new touch screen is now properly set up! We’ll go

over more ways to make it easier to use in the following tutorial,

but it’s basically portable now and ready to have other projects,

such as the PiPhone or PiCam, loaded onto it.

Once you’ve done the calibration,

you can try out a drawing test to

see how the screen reacts

Tips | Tricks | Hacks

Need a better way to watch video on the go? Let

your newly powered-up touch-screen Pi play

your favourite ﬁ lms and shows

Portable Pi video player

We’ve got a Raspberry Pi that we can

make portable now – but how can you

use it? The easiest thing to do with it is

use it as a portable video player. It has a

far superior battery to your phone and has

the added bonus of being easily plugged

into a TV once you reach your destination.

Before we can use it to play the

videos, though, we need to make it a

bit more friendly to transport and get

it to play videos in a particular way. So

we’ve recommended some excellent

accessories and extras you can take

advantage of to achieve this.

01Install VLC

Go to your SSH terminal and install VLC media player.

It’s a lightweight, highly customisable media player that is

able to play just about anything you throw at it. Do this with:

$ sudo apt-get install vlc

02Default settings

Here’s where it gets a bit tricky, as you’ll need to

perform this step via the screen. Hook the Pi up to a display,

mouse and keyboard or just use the mouse and keyboard on

the small screen. Go to an AVI or MP4 ﬁ le and right-click on it,

go to Properties>Open with… and choose Customise for the

next step.

What you’ll need

Q SD card with up-to-date

version of Raspbian

Q PiTFT, fully assembled

bit.ly/1jHEJT4

100 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

03 Set the default

Go to Sound & Video to select VLC from the menu.

Click the checkbox to set it as the default app and then press

Enter to save the changes. Now when you double-click or

tap on the video, it will automatically play in VLC.

04 VLC options

Open up VLC from the menu and right-click anywhere

in the player space to open the Context menu. From here, go

to Tools and then Preferences. Scroll down to click on ‘Allow

only one instance’ and then go to the Video tab and click on the

Fullscreen checkbox. Press Enter to save.

05 Play videos

You’re done! It will play videos at the size of your

Raspberry Pi screen and only one player will exist at a time.

You may have better luck if you convert videos to 320x240, but

it should play much larger videos just ﬁ ne.

06 USB storage

A lot of Raspberry Pi SD cards have limited space, so it

makes sense to keep your videos separate. Make sure to use

storage that does not require any extra power, like a USB stick or

portable hard drive. Access the storage from the File Manager,

as no other mounting is required.

07 Get some protection

The PiTFT PiBow case from Pimoroni is one of the few

cases – if not the only case – that houses the Raspberry Pi with

the PiTFT screen. It’s assembled in layers and only works with

the revision 2 Raspberry Pi (the newer one with 512MB of RAM);

this one won’t have the pins between the yellow video port and

headphone port.

08 Independently powered

To have it working on the go, you’ll need to have it set

up so that you can remove it from a tethered power source.

Portable, USB batteries are quite common these days, but

there are certain things you need to look out for, such as high

capacity and higher amp output.

09 Next time…

Now we have our portable Raspberry Pi video player!

Use it as you wish and learn the ins and outs of the touch

screen in the process. Next month we’ll demonstrate how you

can change the setup from watching video to capturing video

with our RasPi Camera.

Raspberry Pi Tips, Tricks & Hacks 101

Tips | Tricks | Hacks

102 Raspberry Pi Tips, Tricks & Hacks

Build your own looping drum machine

with only 200 lines of code!

Make a Raspberry

Pi sampler

In this tutorial we combine electronics, music and

programming knowledge to create a simple sampler with

looping capabilities. The implementation used in this article has

three drum sounds as the samples, but it is trivial to add more

until you run out of GPIO pins.

Before we start, let’s cover some basic musical terms. Music is

split into bars. There are a certain number of beats in a bar. This

sampler uses the 4/4 time signature, which means there are 4

beats in each bar. Tempo is the speed at which music is played,

and it is measured in beats per minute (bpm). A metronome is an

audible tone that is heard at the start of every beat.

Quantization is the process of aligning notes to beats, or exact

fractions of a beat, and a quantization value is usually given in the

form 1/8. This means that there are eight possible places in a bar

where a note can be played. When the sampler is recording and

a sample button is pressed, we store the sample at the current

position in the bar with the accuracy of the quantize value.

There’s a lot to cover, so let’s get started.

01Connect LEDs

The circuit diagram is an LED that can be turned on and

off with a GPIO output. The orange wire is the connection from

the GPIO output. This then goes through a 220û resistor to limit

the current draw to a safe level. This current ﬂ ows through the

positive leg of the LED and then back to ground. We need nine

LEDs for this project.

What you’ll need

Q Latest Raspbian image

raspberrypi.org/downloads

Q At least one breadboard

Q Push buttons

Q LEDs

Q Female-to-male GPIO

jumper cables

Q Male-to-male GPIO

jumper cables

Left Extra breadboards are

used here to keep the main

breadboard as free from

wires as possible

Raspberry Pi Tips, Tricks & Hacks 103

Tips | Tricks | Hacks

02Wire up buttons

The second circuit we need is a

push button. The purple wire goes to a

GPIO input. There is a 10Kû pull down

resistor to ground, which represents

a logical 0. When the push button is

pressed, the 3.3V supply representing a

logical 1 is connected to the purple wire.

The electricity takes this path because it

has less resistance than the path to

ground. We need two buttons for record

and undo, and then as many buttons as

you like for samples (three drum samples

are provided).

03 Download samples

Create a few folder for the

project called pisampler. Then download

and unzip the sounds:

mkdir pisampler

cd pisampler

wget http://liamfraser.co.uk/lud/

pisampler/sounds.zip

unzip sounds.zip

There will now be a folder called sounds

with some samples in. The ﬁ le format for

samples is .wav audio, Microsoft PCM,

16 bit, stereo 44100 Hz. Mono will work

too. Any samples can be converted to this

format with Audacity by exporting them as

a .wav ﬁ le.

04 Import required libraries

Create a ﬁ le called pisampler.

py in your favourite editor. The ﬁ rst thing

we need to do is import the required

libraries and set some conﬁ guration

values. A key option is debounce: the time

to wait before a button can be pressed

again to stop accidental presses from

contact bounce.

05 Create a sample class

We’re going to use a class to

represent each sample. It's going to need

a few things: the pin that the sample

button is connected to, the name of the

sound ﬁ le, and a reference to the instance

of the sampler class. We haven’t created

the sampler class yet, but the sample

will need to be able to tell if the sampler is

recording or not, and have access to the

data structure that recordings are stored in

to add itself to it if necessary.

The other thing that we need to do

is set the GPIO pin to an input, and add

an event listener for when the button is

pressed. We set callback (the function to

be executed when the button is pressed)

to a function called self.play_btn, which

import RPi.GPIO as GPIO

import time

import pygame

import os

beat_leds = [2, 3, 4, 17]

bar_leds = [27, 22, 10, 9]

record_led = 11

record = 19

undo = 26

debounce = 200 # ms

class Sample(object):

def __init__(self, pin, sound, sampler):

self.sampler = sampler

self.name = sound

self.sound = pygame.mixer.Sound(os.path.join('sounds', sound))

self.pin = pin

GPIO.setup(pin, GPIO.IN)

GPIO.add_event_detect(self.pin, GPIO.RISING, callback=self.play_btn,

bouncetime=debounce)

def play_btn(self, channel):

self.sound.play()

s = self.sampler

if s.recording:

s.recording_data[s.bar_n][s.quantize_n].append({'loop' : s.loop_count,

'sample' : self})

class PiSampler(object):

def __init__(self, tempo=80, quantize=64):

pygame.mixer.pre_init(44100, -16, 1, 512)

pygame.init()

self.quantize = quantize

self.tempo = tempo

self.recording = False

self.record_next = False

self.metronome = False

self.met_low = pygame.mixer.Sound(os.path.join('sounds', 'met_low.wav'))

self.met_high = pygame.mixer.Sound(os.path.join('sounds', 'met_high.wav'))

self.met_low.set_volume(0.4)

self.met_high.set_volume(0.4)

self.samples = []

self.recording_data = []

for i in range(0, 4):

bar_arr = []

for i in range(0, quantize):

bar_arr.append([])

self.recording_data.append(bar_arr)

GPIO.setmode(GPIO.BCM)

for pin in beat_leds + bar_leds + [record_led]:

GPIO.setup(pin, GPIO.OUT)

GPIO.setup(record, GPIO.IN)

GPIO.add_event_detect(record, GPIO.RISING,

callback=self.record_next_loop,

bouncetime=debounce)

Full code listing (Cont. on next page)

Step 04

Step 05

Step 06

104 Raspberry Pi Tips, Tricks & Hacks

06 The sampler init method

Here’s the start of the sampler class. The

last value in the Pygame mixer init is the buffer size.

You might need to increase this to 1024 or higher if

you have audio dropouts. We create some variables

to store recording state. Metronome sounds are then

added and their volume lowered. We also create a list

to hold our samples in.

We create nested arrays to represent recorded

sample presses. There is an array for each bar. Each

bar has an array for each possible quantize value.

The default value of 64 gives us 64 possible places to

store a sample hit per bar.

Finally, we set up the LED pins, and the pins for the

record and undo buttons.

07 The tempo property

The tempo variable is actually a property

with a custom setter. This means when a value is

assigned, it does a custom action. In our case, we need

to calculate how often we need to check for recorded

notes to play in the main loop that we’ll write later.

08 Helper functions

There are a few helper functions in the

class. One of them simply adds a sample to the list of

samples. Another sets a variable to trigger recording at

the start of the next loop. There is also a function which

turns the red LED on when the recording variable is set

to true. Now we'll jump forward and take care of the

main loop towards the end of the full code listing.

09 Start the main loop

The main loop doesn’t actually have to do

any work at all to play sounds, as that’s done by the

GPIO event handlers. The main loop is used to play the

metronome, update the state about which bar/beat/

quantize we are currently on, update the LEDs and deal

with recording if necessary.

Before the loop, we create variables to track the

state. The last recorded loop is a list that we will use

as a stack. A stack is a last in/ﬁrst out data structure,

allowing us to undo recordings multiple times by

removing each sample that was recorded when the

loop count was the value on the top of the stack.

If we’re at the start of a new beat then we use a

function called do_leds that we haven’t created yet.

As the LEDs work in the same way (a block of four LEDs

where only one is turned on), we can use the same

function twice and just pass a different set of pins,

and the index of the LED we want to turn on. We then

call the do_metronome function which will play the

appropriate metronome sound.

We then do some recording logic which starts

recording if we should be recording, and stops

recording if we have just been recording, adding the

GPIO.setup(undo, GPIO.IN)

GPIO.add_event_detect(undo, GPIO.RISING,

callback=self.undo_previous_loop,

bouncetime=debounce)

@property

def tempo(self):

return self._tempo

@tempo.setter

def tempo(self, tempo):

self._tempo = tempo

self.seconds_per_beat = 60.0 / tempo

self.quantize_per_beat = self.quantize / 4

self.quantize_seconds = self.seconds_per_beat / self.quantize_

per_beat

def add(self, sample):

self.samples.append(sample)

@property

def recording(self):

return self._recording

@recording.setter

def recording(self, value):

self._recording = value

GPIO.output(record_led, value)

def record_next_loop(self, channel):

self.record_next = True

def play_recording(self):

for sample_dict in self.recording_data[self.bar_n][self.

quantize_n]:

if sample_dict['loop'] != self.loop_count:

sample_dict['sample'].sound.play()

def undo_previous_loop(self, channel):

if len(self.last_recorded_loop) == 0:

print "No previous loop to undo"

return

print "Undoing previous loop"

loop = self.last_recorded_loop.pop()

for bar in self.recording_data:

for quantize in bar:

removes = []

for sample in quantize:

if sample['loop'] == loop:

removes.append(sample)

for sample in removes:

quantize.remove(sample)

def do_leds(self, leds, n):

count = 0

for led in leds:

if count == n:

GPIO.output(led, True)

else:

Full code listing (Cont.) will play a sound and add it to the recording data if we

are recording. It will become clear how this works once

we’ve written the sampler class. Note that the GPIO

event handler passes the pin that the event handler was

triggered on, hence the channel variable that is present

but never used.

Step 06

Step 07

Step 08

Step 13

Step 11

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 105

11 Lighting LEDs

The LED code is simple. It simply goes through

each pin in the list you provide it with and lights up the

appropriate LED, ensuring that all of the others are

turned off.

12 The metronome

The metronome simply plays a high tone on the

ﬁ rst beat or a lower tone on the remaining beats if the

metronome variable is set to true.

13 The recording code

Looking back at the sample class we created at

the start, you can see that if recording is enabled, and

a note is pressed, then we add a dictionary to the list

of samples for the current bar at the current quantize

point. The dictionary contains a reference to the

sample so that it can be played, and also the loop that

it was added on so that it can be removed if necessary.

The code for playing and undoing recordings can be

seen below.

Note that we directly play the sound rather than

using the btn_play function so that we don’t trigger the

recording logic when playing recorded sounds.

The pop function in undo_previous_loop removes

the last thing that was added to the stack, which will

be the loop count. We then go through every possible

recording data point and remove anything recorded on

the loop we want to remove.

14 Finishing it off

To ﬁ nish it off, we need to add a main function

where we load some samples in and then start the

main loop. Remember that you need to run the code

with sudo python2 pisampler.py because we need sudo

to access the GPIO. Happy jamming!

15 Possible improvements

There are a number of improvements that

could be made to the sampler. Here are a few to get

you started:

• A button to turn the metronome on and off

• The ability to time stretch samples (such as chords)

to ﬁ t with the tempo

• The ability to pitch shift samples on the ﬂ y

• Using a shift register to use less pins when lighting

the LEDs, allowing more inputs

• The ability to save recorded beats so that they can

be loaded and played back

GPIO.output(led, False)

count += 1

def do_metronome(self):

if not self.metronome:

return

if self.beat_n == 0:

self.met_high.play()

else:

self.met_low.play()

def run(self):

self.loop_count = 0

self.last_recorded_loop = []

self.bar_n = 0

self.beat_n = 0

self.quantize_beat_n = 0

self.quantize_n = 0

while True:

if self.quantize_beat_n == 0:

self.do_leds(beat_leds, self.beat_n)

self.do_leds(bar_leds, self.bar_n)

self.do_metronome()

if self.quantize_n == 0 and self.bar_n == 0:

if self.record_next:

self.recording = True

self.record_next = False

elif self.recording:

self.recording = False

self.last_recorded_loop.append(self.loop_count)

self.loop_count += 1

self.play_recording()

time.sleep(self.quantize_seconds)

if self.quantize_beat_n == self.quantize_per_beat - 1:

self.quantize_beat_n = 0

self.beat_n += 1

else:

self.quantize_beat_n += 1

if self.quantize_n == self.quantize - 1:

self.quantize_n = 0

else:

self.quantize_n += 1

if self.beat_n == 4:

self.beat_n = 0

self.bar_n += 1

if self.bar_n == 4:

self.bar_n = 0

if __name__ == "__main__":

sampler = PiSampler(tempo=140)

sampler.add(Sample(05, 'kick01.wav', sampler))

sampler.add(Sample(06, 'snare01.wav', sampler))

sampler.add(Sample(13, 'clhat01.wav', sampler))

sampler.metronome = True

sampler.run()

Full code listing (Cont.)

10 Main loop continued

This code is at the indentation level after

the “while True:” statement. After dealing with the

recording logic, we need to play any notes that have

been previously recorded. We’ll work out how to do

that later on. After that, we can sleep until the next

quantize change is due. Once this happens, we have to

do logic that deals with the quantize and any related

variables such as the beat or bar if necessary, either

incrementing them or resetting them if necessary.

Step 09

Step 10

Step 14

Step 12

Step 11

loop number to the last_recorded_loop stack. We

increment the loop count after doing this.

Tips | Tricks | Hacks

What you’ll need

Q Jumper wire

Q 2mm wire

Q Heat shrink tubing

Q Soldering iron

Q Wire cutters/strippers

Q Hair dryer/heat gun

Q PiRadio bit.ly/1MWkxwp

Q PirateRadio.py script

bit.ly/1SkkeCh

Take advantage of the interference-blocking

feature and make your mark on the airwaves

Build a radio

transmitter

Back in the 1960s, offshore boats were used to broadcast

what was then known as ‘pirate’ radio: unlicensed broadcasts

that provided an alternative to the BBC’s light program (as the

most populist radio station was then known). Pirate radio was a

revolution that inspired Radio 1 and commercial broadcasting, but

these days you don’t need a boat to pursue your radio DJ dream –

just a Raspberry Pi.

Add a basic DIY antenna, an SD card with some MP3 tunes

saved to it, plus a script to automate playback, and you can follow

in the footsteps of John Peel and Tony Blackburn.

This is a 50-50 project, one that has a chunk of DIY as well as

the usual SD card ﬂ ashing. You’ll also need a battery pack, so we

would recommend trying the project on p.76 to make sure you’re

always powered up on the go.

One word of warning: unlicensed broadcasting on the FM

band is an offense. This tutorial is merely a proof of concept –

one that might be used for a school radio project, for instance.

01 Gather your equipment

Begin by downloading the PiFM image. This is over

2.3GB, so if you’re on a slower connection then you’ll need to

get it downloaded in advance.

Meanwhile, source an antenna. This might be a wire coat

hanger or 2mm wire from your local electronic component

store. While you’re there, grab some heat shrink tubing and

some jumper cables, ensuring that you’re well prepared to

start the project.

Below Our home-

made antenna may

look a little rough

around the edges,

but it works great!

Full code

FileSilo.co.uk

Okay, so you’ve already

got a suitable case for

your Raspberry Pi, but

why not go all-out and put

together a new case for

this project? One idea is to

take inspiration from the

broadcast motif and design

an old-style antenna case,

with the Pi and the genuine

antenna cleverly hidden

inside it. Alternatively, a

Mason jar (or other suitably

wide-necked jar) will also

make a great home for the

PiFM – just drill a hole in the

lid for the antenna!

Build a case

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 107

Tips | Tricks | Hacks

02 Prepare MP3 ﬁ les in advance

There’s no facility for live broadcast. Instead, you will

need to arrange your MP3 ﬁ les in advance. These will be played

using a script and transmitted to the nearest radio.

Planning on some DJ-ing? All is not lost, as you can produce

your own MP3 ﬁ les using Audacity or similar open source audio

production tools. To get the ﬁ les to play in a particular order,

number them, or the folders, sequentially.

03 Power your Raspberry Pi radio

Planning to try this out in a remote area? You’ll need

a battery pack to power your Raspberry Pi, or else run it from

your car’s cigarette lighter. For ﬂ exibility, you may also need a

mobile device with SSH software to wirelessly connect to your

Raspberry Pi pirate radio in headless mode.

Of course, the project doesn’t have to be portable and you

can power your Raspberry Pi as usual.

bulk. As you only need a single 200-250mm length, the best

option is to use a handheld rotary blade (or hacksaw) to cut

the length from a wire coat hanger.

Unlicensed broadcasting on the

FM band is an offence. This tutorial

is merely a proof of concept – one

that might be used for a school radio

project, for instance

05 Connect the jumper

Strip the wire from a female jumper, leaving enough to

solder the 2mm wire to.

Once cooled, add a 50mm length of heat shrink tubing to

the top of the jumper and the lower portion of the antenna to

insulate the connection. This will tighten as you apply heat from

a hairdryer or heat gun. Be careful when heating, as the antenna

will warm up and can burn your ﬁ ngers.

04 Prepare your broadcast antenna

To broadcast from your Raspberry Pi, you’ll need a

suitable antenna. Electronic retailers stock copper wire that’s

around 2mm in diameter, but this is usually only available in

Left Prepare MP3

ﬁ les in advance or

make your own using

Audacity, or a similar

open source audio

production tool

108 Raspberry Pi Tips, Tricks & Hacks

08 Copy your MP3 ﬁ les to SD

You cannot simply dump your MP3 ﬁ les on the SD card.

With your ﬂ ashed SD card still inserted into your PC card reader,

browse to the /Pirate Radio partition of the card and paste your

copied ﬁ les.

Beyond simply pasting in numbered MP3s, you can also drop

in named folders from your music collection containing entire

albums or artist catalogues.

09 Conﬁ gure the Pirate Radio

With the SD card still inserted into your PC, open the

pirateradio.conﬁ g ﬁ le in a text editor. Look for the frequency

setting and adjust this as necessary. You’ll need to set this to a

frequency that is currently unoccupied, so switch on your FM

radio, ﬁ nd some free space and change the pirateradio.conﬁ g ﬁ le

as necessary. Save and exit the ﬁ le when you’re done.

10 Random and continuous music

Should you plan to add a lot of music to your SD card

for playback on your pirate radio project, you may want to use

the shufﬂ e and repeat_all settings in the pirateradio.conﬁ g

ﬁ le. By default these are set to true, but to disable, you simply

need to change true to false.

Save when you’re done, and remember to unmount the SD

card before removing it from your computer.

11 Stereo or mono?

The pirateradio.conﬁ g ﬁ le offers you the choice of setting

a true or false value to the stereo_playback value. You should

consider this carefully, as it will determine quality and range for

your broadcast.

Set to true, the broadcast will be of superior audio quality.

However, the range will be reduced as additional power is

Throughout the

tutorial, we’ve talked

about audio ﬁ les as

MP3s, but one of

the many beauties

of the PiFM project

is that it supports

other formats. These

are re-encoded as

required in time for

broadcast, based

on a playlist created

when the Python

code scans the SD

card for audio ﬁ les.

In addition to MP3s,

you can cue up and

broadcast ﬁ les in

FLAC, WAV, M4A,

AAC and WMA.

Multiple

audio

formats

07 Prepare your SD card

As with all Raspberry Pi projects, it’s good to start with

a freshly ﬂ ashed SD card. To get started quickly, use the disk

image linked in the kit list, extract the ISO ﬁ le and ﬂ ash. However,

if you would rather spend some time tweaking the script, ﬂ ash

Raspbian Wheezy and install PirateRadio.py from GitHub.

06 Connect the antenna

The antenna is connected to pin 4 on your Raspberry

Pi’s GPIO. Before you do this, check that your Raspberry Pi case

is suitable for high proﬁ le GPIO connections. If not, consider

connecting it to a short length of wire and mounting it on top of

your case with an adhesive like Sugru, or perhaps just tape it to

the side of your case. As long as the antenna has a connection to

pin 4, you’re good to go.

Above The original

GPIO 4 hack was

discovered by two

students at Imperial

College London

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 109

Tips | Tricks | Hacks

12 Appreciate the law

It’s all too easy to get into trouble with this project, so

before you start broadcasting make sure you’re familiar with

the law and licensing requirement for broadcasting on the FM

band. This project is perfect for short range use, such as playing

your MP3s on an old car radio, although you’ll have to modify the

length of the antenna for this. Schools may also beneﬁ t from a

Raspberry Pi radio station.

13 Take to the airwaves!

Insert your SD card into the Raspberry Pi and plug the

device in. Meanwhile, step away from the device and head into

the next room with your FM radio and tune into the speciﬁ ed

frequency. Once the Raspberry Pi has booted you should ﬁ nd

that the MP3 ﬁ les are being broadcast!

14 Troubleshooting bad broadcasts

Problems with your broadcast? Check the FM radio is

capable of picking up other stations. If you’re in the UK, look for

Radio 2 on 88-91 FM, which can be received virtually anywhere.

You should also check the frequency setting in the pirateradio.

conﬁ g ﬁ le. Remember that the band is accessible in the UK from

87.5-108 FM. As such, you cannot access frequencies beyond

these points on an FM radio.

Raspberry Pi, but equally it won’t result in audio being broadcast

to your FM radio!

Interference in the broadcast may be due to wireless routers

and microwave ovens. Your Raspberry Pi’s power source may

also cause problems.

16 Elevate your broadcast

You can improve the range by positioning your

Raspberry Pi and the PiFM antenna in an elevated position. You

might, for instance, place it by an upstairs window.

Even better results can be achieved by broadcasting from

up a tree or on a hillside – but keep in mind that an unlicensed

project really needs to maintain a short range.

17 Curb your piracy

You’ve built a compact, potentially portable radio

transmitter, but remember that it isn’t the 1960s and you’re not

a revolutionary. Consider the approved uses for the project and

stick to these, rather than using it to cause mischief and get a

criminal record. You could make an FM repeater, for example,

or create a wireless mic. If you really want to get on the radio,

consider volunteering with your local community station.

Spread-spectrum

clock signals on the

GPIO pins are the

secret power behind

the Raspberry Pi’s

surprising hidden

ability to broadcast

on the FM band. By

utilising this energy

with an antenna on

pin 4, you can turn a

method employed

to reduce electrical

interference with

other devices

connected to and

situated near your

Raspberry Pi into

a tool for radio

communication.

How does

the Pi

broadcast?

This project is perfect for short

range use, such as playing your

MP3s on an old car radio, although

you’ll have to modify the length of

the antenna for this

Left Check out

Ofcom’s radio

broadcasting

licenses for more

details on the

law regarding

broadcasting music

required. So setting stereo_playback to false will increase your

broadcast’s range. However, due to the scale of the transmitter,

this is only a matter of 20 feet!

15 Check your antenna for problems

Reception issues may be traced back to the antenna.

Double-check the soldering is secure and conﬁ rm that the wire

is connected to GPIO 4. Using the wrong pin won’t harm your

Tips | Tricks | Hacks

Need the internet on your Pi on the go? Try out a physical

tether to your Android device for instant online access

Tether your Raspberr y

Pi to an Android device

The portability of the Raspberry Pi is one of its most lauded

features and you can get many different accessories to help

aid this portability. Mini screens, mini wireless keyboard and

mouse combos, portable batteries and more can get you out

and about, but the Internet is a stumbling block that you can’t

easily ﬁ x with an accessory. What you do also usually have

with you is an Internet-connected magic pocket box called a

smartphone that, with a bit of know-how, you can connect the

Pi to and steal some Internet from. Over the next two pages

we will impart this know-how to get you using your Raspberry

Pi on the Internet when you’re on the go.

01 The easy way

A lot of smartphones now have a Wi-Fi hotspot feature,

which the Raspberry Pi can easily attach to. First of all, turn the

hotspot on and then boot into the Pi. Connect a wireless dongle

and open up the wpa_gui in Preferences>Wi-Fi Conﬁ guration.

02 Scan for device

Click Scan to open up the scan window and then select

Scan again from inside there. It should pick up your device –

connect it as you would to any Wi-Fi network and the Pi will

remember it for when it needs it next.

What you’ll need

Q Android device

Q USB cable

110 Raspberry Pi Tips, Tricks, & Hacks

Raspberry Pi Tips, Tricks, & Hacks 111

Tips | Tricks | Hacks

03 Set up tether

First connect your phone to your Raspberry Pi via a USB

cable – depending on the amount of power your Pi has, it might

have trouble charging your phone but it will still let you tether. In

the tethering menu you can now activate USB tethering.

04 Check connection

Your Android device will create an interface known

as eth0 on the Raspberry Pi. You can check to make sure this

is happening, and that it will let you tether, by opening up a

terminal and typing the following:

$ ifconfig

05 Quick connect

You can connect from the terminal right now to

access the Internet. You should be able to do this by typing the

following into the terminal:

$ sudo dhclient usb0

This will automatically grab any available IP address that your

phone will give to it.

06 Test connection

There’s a few ways to test your connection. We’d usually

stay in the terminal and ping www.google.com, which you can

do, or you can click on the browser and see if it loads the page.

07 Save the settings

Once you reboot your Pi, it won’t remember to

automatically connect to the phone’s tether. However, we can

add an entry to its conﬁ g so that it will try and do this in the

future. From the terminal use:

$ sudo nano /etc/network/interfaces

08 Interface settings

Here you’ll ﬁ nd all the current network settings – yours

might look different from ours depending on if you have added

any ﬁ xed wireless settings or passthroughs. Using the same

syntax as the eth0 line, add:

iface usb0 inet dhcp

09 Tether on the go

After a save and reboot, your Pi should now

automatically connect to your phone, whether it’s via Wi-Fi

hotspot or a physical connection. It may draw a little more

charge than usual while tethering, so be sure to keep an eye on

your battery level.

Above It’s usually

easy to ﬁ gure out

which device is your

phone – set it right

next to the Pi and it

will be the one with

the best signal!

Using your Pi on

your mobile phone

will eat up data

much faster than

browsing on your

phone normally

is. We suggest not

doing a full software,

distribution or

ﬁ rmware update

if you don’t want

to spend a fortune

on data. You can

also set limits on

the amount of data

used on your phone

to save yourself any

problems, and a

physical tether will

allow you to connect

via the phone’s Wi-Fi

if that’s an option.

Mobile

data

Tips | Tricks | Hacks

112 Raspberry Pi Tips, Tricks & Hacks

Learn how to set up a network of Raspberry Pis

with centralised authentication and ﬁle storage

Build a network of

Raspberry Pis

In this tutorial, we’ll learn to set up a Network

Information Services server on a Raspberry Pi

that centralises some of the configuration of

Linux systems. This includes user accounts. This

means that we can set up users on the Raspberry

Pi server and have them available on each

client Raspberry Pi. This arrangement would

be useful in a classroom situation where there

were a number of Raspberry Pis shared between

classes. Each child would have a username and

password, and they would have access to all

of their ﬁles from any Raspberry Pi once they

have logged in. One big advantage of this is that

each user’s ﬁles can be backed up from a single

place. We’ll also be giving some examples of

software that could be used in a classroom on the

Raspberry Pi.

We’ll be using the latest Raspbian image as the

operating system for both our Raspberry Pi server

and Raspberry Pi clients, so we’ll need to start by

writing that to two SD cards. Note that we’ll be

making a master SD card for the clients which can

then be written to the rest of the SD cards, so only

write the image to two of them.

The instructions for ﬂashing an image to an

SD card can be found at www.linuxuser.co.uk/

tutorials/how-to-set-up-raspberry-pi/. You will

only need to go up to the step where you write

the image to the SD card. Note that you will have

to adapt the instructions slightly for using the

latest Raspbian image rather than the Debian

one. The image that we used was 2012-09-18-

wheezy-raspbian.zip.

We are going to assume that you are plugging

the Raspberry Pis into an existing network

with DHCP, a protocol for handing out network

settings to devices that connect to said network.

This way, they can get access to the internet for

installing packages and other useful things such

as teaching resources.

Resources

At least 2 Raspberry Pis

with appropriate peripherals

(Note that the server Raspberry Pi will

only need a power and Ethernet cable

connected once conﬁgured)

SD card

Computer

Network switch

Ethernet cable

Storage device

The Network

Information Services

and Network File

System server

providing centralised

authentication and file

storage to the clients

A network switch

connecting each

device to the network

An external storage

device connected

to the server to

periodically back

up each user’s files

The client Raspberry

Pis that all use the

same master image

and pull the rest of

the data from the

server, making it very

easy to add more or

replace an SD card

should it get broken

Raspberry Pi Tips, Tricks & Hacks 113

Tips | Tricks | Hacks

01 Initial conﬁ guration of the server

Raspberry Pi

Connect a keyboard, mouse, Ethernet cable,

monitor and, lastly, power to your server

Raspberry Pi. Raspbian will boot and a

conﬁ guration menu will be displayed. You

need to select the option to expand_rootfs to

make sure that you’re using the entire space of

the SD card. You should deﬁ nitely change the

password for the pi user so that no one can log

into your server with the standard credentials

of Username: pi and Password: raspberry. Then

change the memory split to 240MiB for ARM and

16MiB for the VideoCore. Finally, enable SSH,

then select ‘Finish’. Select ‘Yes’ to reboot now.

02 Fire up your Linux computer

Now that we have enabled SSH on the

server Raspberry Pi, we can configure it remotely

using SSH as long as your Linux computer is on the

same network (if not, connect it now). We might

as well make sure that SSH works now for when

a monitor is no longer needed. During the boot

process of Raspbian, a message will be displayed

with the current IP address of the Pi. Open up a

terminal on your Linux computer and type ‘ssh pi@

[your Pi’s IP address]’. Type ‘yes’ when asked if you

want to connect and then enter the new password

that you set. You are now logged into your server Pi.

03 Setting up a static IP address

We highly recommend assigning a

static IP to your server Raspberry Pi because

you, and more importantly the client Raspberry

Pis, will always know where to ﬁ nd it on the

network. We’ll need to ﬁ nd out a couple of

things about your current network setup before

setting a static IP. You can use the commands

‘ifconﬁ g eth0’ and ‘ip route show’ to do this.

We’ve included the important output from our

commands below so that you can see what to

do with each value. Now that we have found out

things about your network, such as your current

IP address, the network mask and so on, we can

set up a static IP address.

Use the command:

sudo nano /etc/network/interfaces

…to edit the networking conﬁ guration ﬁ le. Use

04 Restart the server Pi

Restart the server Pi so that the

networking changes we just made can take

place. Log back in using SSH and the new IP

address that you chose.

05 Installing the required packages

for an NFS server

NFS stands for Network File System, and is what

we’ll use to share each user’s home directory.

Run the command:

sudo apt-get update

……to update the package lists on the device,

followed by :

sudo apt-get install nfs-kernel-

server nfs-common rpcbind

…to install the packages required for an NFS

server. You’ll probably get a message like ‘[warn]

Not starting NFS kernel daemon: no exports....

(warning)’. This is just telling us that the NFS

server hasn’t started because we haven’t set it

up to share (export) any directories yet.

07 Installing NIS

NIS stands for Network Information

Services and used to be called Yellow Pages,

or yp for short. Many of the services and

directories still have ‘yp’ in the name. Use the

command ‘sudo apt-get install nis’ to install

Network Information Services. Accept any

extra packages that may be required. You will

now be taken to the package conﬁ guration

screen for NIS. It will start by asking you to

enter an NIS domain. This can be anything you

like, but we’re calling ours raspberrypi. Once

you have set that, NIS will continue to install

and then the NIS services will attempt to start.

This will take a few minutes and fail, so don’t

worry when that happens. We need to do more

conﬁ guration before it will work.

the arrows to navigate and start by deleting the

line ‘iface eth0 inet dhcp’. Then replace it with

lines similar to the following:

iface eth0 inet static

address 172.17.173.249

netmask 255.255.255.0

gateway 172.17.173.1

Make sure that the IP address you assign to

your Raspberry Pi server isn’t taken. You’ll want

to discuss this with your network administrator

if you have one, but it’s usually safe to assume

that the address the device had already won’t

be taken. You’ll also want to note down that IP

address for future usage.

Save the changes in nano using the key

combination Ctrl+O followed by Enter. You can

exit nano using Ctrl+X.

You might notice that we haven’t done

anything about the DNS server. DNS is used to

resolve hostnames such as google.co.uk to an

IP address. The IP address of the DNS server is

stored in /etc/resolv.conf and will not change

value after changing to a static IP address.

pi@raspberrypi ~ $ ifconfig eth0

eth0 Link encap:Ethernet

HWaddr xx:xx:xx:xx:xx:xx

inet addr:172.17.173.249

Bcast:172.17.173.255

Mask:255.255.255.0

pi@raspberrypi ~ $ ip route show

default via 172.17.173.1 dev eth0

172.17.173.0/24 dev eth0

proto kernel scope link src

172.17.173.249

06 Exporting directories

Add the line:

/home *(rw,sync)

…to the end of /etc/exports using nano. The line

means share the /home directory with everyone,

permitting read and write access. Although

this sounds insecure, other users will only get

read access to directories that aren’t their own

and therefore won’t be able to delete or change

ﬁ les. NFS requires rpcbind, so you need to start

that before NFS. Rpcbind doesn’t start on boot

by default on Raspbian, but we want it to. You

can do this using the command ‘sudo update-

rc.d rpcbind enable’. You can start them both

immediately using the following commands:

sudo /etc/init.d/rpcbind start

sudo /etc/init.d/nfs-kernel-server

start

08 Conﬁ guring NIS

We need to do a few things before our

NIS server will work. The ﬁ rst thing we need to

do is open up /etc/default/nis with nano as we

do in the usual way. Make sure you preﬁ x the

nano command with sudo because we need root

privileges to edit each of these ﬁ les. You need to

change the line:

NISSERVER=false

…to…

NISSERVER=master

…and also change the line…

NISCLIENT=true

…to…

NISCLIENT=false

Save the changes and then exit nano. We then

need to edit:

114 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

11 Preparing the client

We’re pretty much done with the NIS

server for now, so it’s time to start working

on a client image. Connect up the second

Raspberry Pi and insert the SD card with the

fresh Raspbian image on. Raspi-conﬁg will

show as it did when we conﬁgured the server.

The only option you need to use is the one to

expand_rootfs and then select ‘Finish’. Select

‘Yes’ to reboot now.

13 Mounting the server’s home

directory

It’s now time to mount the server’s home

directory as our own. We want to do this at every

boot, so we’ll put an entry in /etc/fstab to make

it permanent. Open /etc/fstab in nano and add a

line in the following format to the end of the ﬁle:

[server ip]:/home /home nfs

defaults 0 0

You can now save the changes and use the

command ‘sudo mount -a’ to mount each entry

in the /etc/fstab ﬁle, therefore mounting the

servers home directory as the clients. If you run

‘ls /home’ you’ll see the home directory of the test

user we created before and also the pi user on

the server.

pi@raspberrypi /home $ cat /etc/

fstab

proc /proc

proc defaults 0

/dev/mmcblk0p1 /boot

vfat defaults 0

/dev/mmcblk0p2 /

ext4 defaults,noatime 0

# a swapfile is not a swap

partition, so no using swapon|off

from here on, use dphys-swapfile

swap[on|off] for that

172.17.173.249:/home /home nfs

defaults 0 0

pi@raspberrypi /home $ ls /home

pi testuser1

14 Becoming an NIS client

You need to open up /etc/yp.conf in nano

(remember to use sudo) and add the lines:

ypserver [server ip address]

domain [nis domain] server [server

hostname]

You also need to edit the /etc/nsswitch.conf ﬁle

to look like ours. Once you’ve done that, you can

reboot the client using the command ‘sudo init 6’.

10 Adding a new user

All users are added on the NIS server. You

can use the command ‘sudo adduser [username]’

to do this, and then ﬁll in the extra information

required interactively. The NIS databases are

updated automatically after adding a new user.

We now need to add the new user to some groups

so they can do things like play audio and so on.

You can do this with the command ‘sudo usermod

-a -G audio,video,plugdev,games,users,netdev,

input [username]’. We have now made more

changes to the user and will have to rebuild the

NIS database manually using:

cd /var/yp

sudo make

You can use the command ‘sudo passwd

[username]’ on the NIS server as the pi user to

change the password of a user. You will have to

rebuild the database again after doing this.

12 Logging in and installing required

packages

Username: pi and Password: raspberry and

then run the command ‘sudo apt-get update’ to

update the package list on the device. Install the

required packages for NFS and NIS clients using

the command ‘sudo apt-get install nis rpcbind

nfs-common’. The NIS domain conﬁguration

screen will show as before, so just set this to

whatever you set it to the ﬁrst time. As before,

the system will fail to start the NIS because we

need to do extra conﬁguration, including setting

rpcbind to start at boot using the command

‘sudo update-rc.d rpcbind enable’. We’re going to

need rpcbind shortly so we might as well start it

now using ‘sudo /etc/init.d/rpcbind start’.

09 Initialising the NIS master

database

Before anything else, restart the Pi using sudo init 6

to let the hostname change take place. Reconnect

once the Pi has booted back up. Run the command:

sudo /usr/lib/yp/ypinit -m

/var/yp/Makefile

…and change the line…

ALL = passwd group hosts rpc

services netid protocols netgrp

…to…

ALL = passwd shadow group hosts

rpc services netid protocols

netgrp

The password ﬁle on Linux contains a list of

users and information like their home directory

and the User & Group IDs. We need to add the

shadow ﬁle as that ﬁle stores password hashes

for users. We also need to change the line:

MINGID=1000 to MINGID=0

…because we’ll be adding our NIS users to

system groups such as audio so that they can

play sound. The next step is to change the

server’s hostname by editing the /etc/hostname

ﬁle. We’re going to change our hostname from

raspberrypi to nismaster. We then need to

change /etc/hosts to complete the hostname

change, as well as add an extra line. We need

to do this because servers running NIS are

added by name rather than their IP address.

You’ll see this shortly. Plus, we should be able to

differentiate the NIS server from all of the other

Raspberry Pis anyway. Change the line:

127.0.1.1 raspberrypi

…to…

127.0.1.1 [your new hostname]

You’ll also need to add a new line for the IP

address of the NIS server in the form:

[IP address] [hostname].[NIS

domain] [hostname]

and then press Ctrl + D followed by Enter. We can

now start the NIS server using the command:

sudo /etc/init.d/nis start

Raspberry Pi Tips, Tricks & Hacks 115

Tips | Tricks | Hacks

19 Backing up the server

One of the main advantages to having

central ﬁ le storage is that everything can be

backed up from one place. More importantly,

ﬁ les that are deleted can be restored. We’ll be

using rsync to perform the backups, so you’ll

need to install that using the command ‘sudo

apt-get install rsync’. We’re going to assume that

you’ve set up your backup area in /mnt/data.

We’ll be using the command

sudo rsync -avP /home /mnt/data

to perform the backups. The switches mean

the following:

a – preserve the permissions and other

properties of the ﬁ le

v – show verbose output

P – show progress

This command syncs any changes from /home

to /mnt/data, but will not get rid of any ﬁ les that

are deleted from the /home directory. Rsync is

very efﬁ cient: only the changes made to a ﬁ le are

copied over, rather than a new ﬁ le. We want to run

this command regularly, say once an hour or so,

so we’ll add it to cron. Cron is a daemon that runs

commands at speciﬁ c intervals according to each

user’s crontab. You can edit the pi user’s crontab

using the command ‘crontab -e’. Add the following

line to the end of the crontab ﬁ le:

0 * * * * ‘sudo rsync -avP /home /

mnt/data’

The crontab ﬁ le takes lines in the format:

minutes hours day-of-month month day-of-

week. The above line tells the cron daemon to

run the command in at the start of each hour.

Save the changes as you usually would in nano.

20 That’s it!

With the project complete, you now

have a central authentication and ﬁ le storage

area that gets backed up, as well as a master

image for the client Raspberry Pis that is

ﬁ lled with useful software. Now you can start

enjoying your network of Raspberry Pis!!

18 Preparing a disk to be used as a

backup area

The instructions for preparing an external disk

to be used as a backup area can be found here:

www.linuxuser.co.uk/features/build-a-file-

server-with-the-raspberry-pi. Use steps 09 to

11 to do this.

15 Log in with a user from the NIS server

Wait for the client to boot up and then

try to log in with the pi user. Remember we

didn’t change the password of the pi user

when we set up the client? We are now going to

be logging in with the pi user from the server,

so the password will be different.

The nice thing about this is that the Pi is still

operable with the standard credentials when

there is no network cable connected or the

server is down. However, it will complain a lot

during the boot process and still won’t be able

to access the home directory on the server.

17 Duplicating the card

Before continuing, shut down the client

Pi by switching to the pi user using ‘su pi’ and

then typing ‘sudo init 0’. Everything on Linux is

seen as a ﬁ le. Because of this, we can simply use

a combination of the cat command and pipes to

duplicate the SD card. Switch to the root user

on your Linux computer using the command

‘su root’. Use the output of ‘fdisk -l | grep Disk’

to ﬁ nd the path of the SD card. Ours is /dev/

16 Installing packages on the client

Linux has a bunch of fantastic

educational software that would be ideal for

use in a classroom. We’re going to recommend

a few programs that would be good to include

on the master client image. There is already a

pretty good collection that comes with the base

Raspbian image, but we can deﬁ nitely add more.

We’re going to install the following software:

AbiWord – A basic word processor

Gnumeric – A basic spreadsheet program

GCompris – Bundle of children’s educational

software packages

mmcblk0. You can back up the card using the

command ‘cat /dev/mmcblk0 > nisclient.img’

and restore the backup to a different card using

‘cat nisclient.img > /dev/mmcblk0’ once you have

taken the original card out.

Galculator – Scientiﬁ c calculator

TuxMath – Maths tutor for kids

Tux Paint – Children’s drawing program

You can install all of this software at once

using ‘sudo apt-get install abiword gnumeric

gcompris galculator tuxmath tuxpaint’. This may

take a while. Once it’s ﬁ nished, you can type

‘startx’ to load the LXDE desktop environment

and have a play around everything on there.

Have a go at logging in as the test user also.

One problem will be that there are no desktop

icons because they are only set for the pi user.

The programs will still be there in the start menu

anyway. When logging out, the users need to log

out of LXDE so that they go back to the console

and then type ‘logout’.

Linux has lots of educational

software, ideal for the classroom

Tips | Tricks | Hacks

Hover is an impressive add-on board for your

Raspberry Pi that allows you to easily add

touch and gesture control to any project

Add gesture control

to your Raspberry Pi

People often ask what the best way is for them to

get started with Raspberry Pi. Obviously this does

depend on the individual user and what they want

to achieve and get out of any project, but in a more

general sense it’s often the hardware projects

that win out for getting to grips with it. They teach

a variety of skills (including programming, circuit

building, soldering, hardware design and much

more) and are also varied enough to both keep

beginners interested and allow them to work out

for themselves exactly what aspect they love

best. Even a seasoned professional will get a

serious kick out of a bit of physical computing and

automation! This is one of the unique features of the

Pi compared to traditional “black box” computers;

you can break out of the usual boundaries and

interface with everyday objects like never before.

One of the most important aspects of a hardware

project is often the user input mechanism, and

as technology is reﬁ ned we see new and more

intuitive ways to accomplish this task. Gesture

and touch control is now present in a large

number of consumer devices and even the biggest

technophobes are starting to embrace the ease of

this technology. It is time to bring your Raspberry Pi

projects into the 21st century with Hover!

What you’ll need

Q Raspberry Pi

Q Hover

Q Breadboard

Q Male to female

jumper cables

Q Speaker or headphones

116 Raspberry Pi Tips, Tricks, & Hacks

Raspberry Pi Tips, Tricks, & Hacks 117

Tips | Tricks | Hacks

01 Get the gear!

The Hover add on board is available to purchase direct

from Hover (http://www.hoverlabs.co/#shop) for $39 (£25),

however this will ship from Northern America and therefore if you

are based in the UK or Europe it will likely be quicker and cheaper

to order from one of the other retailers listed via the above link.

The added beneﬁ t of ordering from a retailer is that if you need

any of the other items you can likely get those at the same time!

Hover will work perfectly with any Raspberry Pi, including both

the new plus versions and the older models – just make sure

your system is fully up to date with:

sudo apt-get update

sudo apt-get upgrade

04 Check the connection

Hover connects to the Raspberry Pi through the

I2C interface located on the main 26 or 40 pin GPIO bank

(depending on which version of the Raspberry Pi you are

using). There is a very easy way to check if your Raspberry Pi is

correctly connected to Hover using the simple command line

I2C tools. Issue the following command:

sudo i2cdetect -y 1

If you see 42 in the response then you are successfully

connected to Hover!

03 Set up the hardware

Make sure your Raspberry Pi is powered down and

not connected to power before starting this step, to avoid any

unnecessary damage to your Raspberry Pi. Pick up your Hover,

breadboard and wires and connect the as shown in the Fritzing

diagram. The physical pins you should be using on the Raspberry

Pi are 1, 3, 5, 6, 16 and 18. Whilst a Model B Pi is shown, this will

be the same connection on a Model A, B, A+ or B+ of any revision.

Once completely set up like the image, reconnect the power cord

and open an LXTerminal session.

02 Update GPIO and I2C

When making use of GPIO and I2C (or any other

interfacing technique on the Raspberry Pi) it is always good

practice to update to the very latest software versions possible.

Newer versions typically have bug ﬁ xes and additional futures

which can come in very handy. GPIO and the RPi.GPIO Python

library are installed by default on Raspbian, but you may need to

enable I2C if you haven’t already. This is a fairly standard process

and has been covered many times so we won’t go into it here. We

would, however, highly recommend the brilliant I2C setup tutorial

from Adafruit (https://learn.adafruit.com/adafruits-raspberry-

pi-lesson-4-gpio-setup/conﬁ guring-i2c).

Above You can tap

the Hover or swipe

in four directions

just above it

The physical pins you

should be using on

the Raspberry Pi are

1, 3, 5, 6, 16 and 18

The Hover board

has intelligent on-

board level shifting,

meaning that it can

be used with either

3.3V or 5V logic

levels which means

it can be used with

pretty much any

microcontroller your

heart desires. There

are connection

examples and

code snippets

available for

Arduino, Sparkcore

and PCduino on

the Hover website

(hoverlabs.com) and

these can also be

adapted to suit other

devices fairly easily.

If you decide to

create your own

example with

another device then

why not submit a pull

request to the Hover

GitHub (github.com/

jonco91) if you are

happy to share!

Plenty of

platforms

Tips | Tricks | Hacks

118 Raspberry Pi Tips, Tricks, & Hacks

Above This MGC3130

chip works as the 3D

tracking and gesture

controller

07 Run the example file

The current Hover library is simply a Python ﬁ le

with all of the necessary functions included within it, rather

than an installable package (however, this may change in

the future). In order to use the functions contained within

the Hover_library.py script discussed above, it is therefore

necessary to make sure that the Hover_library.py script is

located in the same folder as any script you have written that

makes use of any of the Hover functions. In a terminal session,

navigate to the folder containing the Hover_example.py ﬁ le

and run it using:

sudo python Hover_example.py

The Hover board will initialise and you will then see a message

“Hover is ready”, meaning you are good to go.

05 Using a Rev 1 Pi?

In the code, we have passed an option “-y 1” which tells

the operating system which I2C bus to look at (there are two on

the BCM2835 processor on the Pi). The ﬁ rst revision Raspberry

Pi (the one that initially launched in February 2012 with 256MB

of RAM) made use of I2C bus 0, whereas all other versions of

the Raspberry Pi since have used I2C bus 1. So the above code

would change to:

sudo i2cdetect -y 0

And you should expect the same output (42) as in step 7.

Additionally you will need to edit line 27 of the Hover_library.

py ﬁ le, changing bus = smbus.SMBus(1) to bus = smbus.

SMBus(0). A patch that automatically detects the Raspberry

Pi version and makes this change for you has been submitted,

but not yet accepted into the master branch so this may not be

necessary in future versions.

06 Download the sample code

Now you have everything hooked up correctly and

your Raspberry Pi is fully up to date, it is time to get the

Hover Python library, which makes using the board from

Python scripts extremely easy. You can get this using the

following command:

git clone https://github.com/jonco91/hover_

raspberrypi.git

This should download a folder called hover_raspberrypi to

your /home/pi directory containing all of the ﬁ les needed for

this article. Alternatively you can download the zip ﬁ le from

https://github.com/jonco91/hover_raspberrypi/archive/

master.zip.

Python is extremely

useful for beginners

due to its easy-to-

understand syntax,

fairly prose-like

formation and the

ﬂ exibility and ease

of acquiring existing

software libraries to

help your projects.

It is also the ofﬁ cial

programming

language of the

Raspberry Pi and is

therefore very well

supported within the

community. That is

not to say that Hover

will not work with

other programming

languages; simply

that the creators of

Hover have not yet

released any code

libraries in other

languages.

Why

Python?

Raspberry Pi Tips, Tricks, & Hacks 119

Tips | Tricks | Hacks

08 Investigate the output

Once you have completed step 7, if you touch the

Hover board or make gestures above it you will begin to see

output in the terminal which is a bunch of 0s and 1s and then

a description of what it has seen – right swipe, north tap,

etc. The way the Hover works is that it can sense any one of

nine different actions and these are sent to the Raspberry Pi

over I2C as an 8-bit binary value. The ﬁ rst three bits describe

whether it was a touch or gesture event and the remaining ﬁ ve

bits describe the speciﬁ c type or direction of the event. The

exact breakdown can be seen in the code listing to the right.

09 Enable 3.5mm audio

Grab your speakers and plug them in to the 3.5mm jack

plug on the Raspberry Pi. You will then need to route audio to

the 3.5mm jack using the following command (you can skip this

step if you are using an HDMI display, which has in-built audio):

sudo amixer cset numid=3 1

10 Make a drum machine

In the hover_raspberrypi folder is another folder called

examples that contains code and sounds to turn Hover into a

drum machine! Navigate to the hover_raspberrypi directory

and then copy the Hover_library.py ﬁ le into the examples folder

by using:

c p Ho ver_lib rar y.py exa m ples

You can then move into the examples folder and run the Hover_

drum.py ﬁ le using:

cd examples

sudo python Hover_drum.py

Make some gestures and taps on and around Hover and you

will have your own basic drum machine!

11 Create your own responses

The great thing about having a Python library available is

that it is easy to integrate this device into any of your existing or

future projects. The code shown is all you need to get started

with Hover. You will see that on line 15 and onwards there are

comments saying “code for … goes here”. Essentially all you need

to do is insert the actions you want to occur on the particular

event mentioned in the comment and you will be up and

running… it really is that easy!

12 Other project ideas

Most of you are probably now wracking your brains for

projects you could use Hover in, but let’s face it – pretty much

any project that requires physical interaction would be made

better with touch and gesture control. If you think it is cool but

are lacking inspiration, we recommend looking at the projects

section of the Hover website at http://www.hoverlabs.

co/projects, where there are projects by the creators and

community alike. If you make something cool, be sure to send

us the pictures!

Did you come

here looking for

information on how

to build your space

age transportation

device? We can’t

help you with

that, but we don’t

want to leave you

disappointed!

Hoverboards were

ﬁ rst popularised as

a ﬁ ctional personal

transportation

method in the 1989

ﬁ lm

Back To The

Future Part II

and

took the appearance

of a levitating

skateboard with no

wheels. 25 years

later and it seems

we might be getting

close to turning this

dream into a reality.

Hendo Hoverboards

have created a

$10,000 hoverboard

which uses a

principle similar

to that of maglev

trains to generate lift

(kck.st/ZMd9AA),

and more recently

Ryan Craven has

created a much

cheaper alternative

using four leaf

blowers and some

other cheap parts

(mrhoverboard.

com/about).

Where are the

hoverboards?

import time

from Hover_library import Hover

hover = Hover(address=0x42, ts=23, reset=24)

try:

while True:

# Check if hover is ready to send gesture

# or touch events

if (hover.getStatus() == 0):

# Read i2c data and print the type of

# gesture or touch event

message = hover.getEvent()

type(message)

if (message == “01000010”):

# code for west touch goes here

elif (message == “01010000”):

# code for centre touch goes here

elif (message == “01001000”):

# code for east touch goes here

elif (message == “01000001”):

# code for south touch goes here

elif (message == “01000100”):

# code for north touch goes here

elif (message == “00100010”):

# code for swipe right goes here

elif (message == “00100100”):

# code for swipe left goes here

elif (message == “00110000”):

# code for swipe down goes here

elif (message == “00101000”):

# code for swipe up goes here

# Release the ts pin until Hover is

# ready to send the next event

hover.setRelease()

time.sleep(0.0008) #sleep for 1ms

except KeyboardInterrupt:

print “Exiting...”

hover.end()

except:

print “Something has gone wrong...”

hover.end()

Full code listing

120 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

Take your Raspberry Pi, HDMIPi and Screenly and

turn them into a beautiful digital photo frame

Make a digital

photo frame

Digital signage is a huge market in modern times, and

increasingly we are seeing digital advertising in the public

space – be it on street billboards, shopping centres and even

in some city taxis. Screenly is an exciting piece of software

from Wireload Inc that has set out to reduce the barriers to

entry of the digital signage market by employing a Raspberry

Pi as its main hardware component for the individual signage

nodes. With the powerful VideoCore IV graphics processor at

the heart of the Pi and its low electrical power consumption,

using it as a digital signage platform is a no-brainer.

Our expert has been using Screenly a lot recently for some

projects and it truly is a really great piece of software. He was

also one of the ﬁ rst backers of HDMIPi on Kickstarter, and when

his reward arrived recently it occurred to him that, together

with Screenly, it would make the perfect home-brew digital

photo frame and another great Raspberry Pi-based hardware

project. In this tutorial, we will show you how to assemble this

powerful hardware/software combination for yourself.

01 Order your items

If you haven’t already got them

in your Raspberry Pi collection, you will

need to order all of the items from the

“What you’ll need” list. The HDMIPi is

currently only compatible with Model B

of the Raspberry Pi, although a Model

B+ version is in the works (the B+

does actually work with HDMIPi, but

unfortunately cannot ﬁ t into the case).

Pretty much any USB keyboard will

work with Screenly, including wireless

ones, so you do not need to worry about

a mouse for this tutorial as it will all be

done from the command line.

Finally, a speaker is only necessary

if you intend to play videos from the

display with sound as well.

What you’ll need

Q Raspberry Pi Model B

Q HDMIPi kit

Q Class 10 SD Card

Q 5.25V Micro USB power

supply

Q USB keyboard

Q Wi-Fi dongle

Q Internet connection

Raspberry Pi Tips, Tricks & Hacks 121

Tips | Tricks | Hacks

04 Flash image to SD Card (Linux)

It’s worth noting the value of having a Linux machine

at your disposal (or a spare Raspberry Pi and SD card reader)

to download the ZIP ﬁ le in Step 03. This is typically the easiest

way to unzip the ﬁ le and copy the image across to your SD

card. Assuming the disk isn’t mounted, open a terminal

session and type:

unzip -p /path/to/screenly_image.zip | sudo dd

bs=1M of=/dev/sdX

Make sure that you replace /path/to/screenly_image.zip with

the actual path.

05 Flash image to SD Card (Other OS)

If you do not have another Linux machine handy, or

a card reader for your Raspberry Pi, you can still do this from

other popular operating systems. On Windows you should use

Win32 Disk Imager and follow the easy to use GUI. From Mac

OS X you have the options of using the GUI-based software

packages PiWriter and Pi Filler, or running some code from the

command line. Visit www.screenlyapp.com/setup.html for

more info.

06 Insert SD card and peripherals

Once the Screenly image has been successfully

transferred to your SD card, you will need to insert it into the

Raspberry Pi within your HDMIPi casing.

It is a good idea to connect your Wi-Fi dongle and keyboard

at this point. Take a look at the image at the top of this

page to see where the slots are in relation to the casing. A

wired network is also required for the initial setup and for

conﬁ guring the Wi-Fi connection.

07 Boot up your Raspberry Pi

The HDMIPi driver board has a power output for the

Raspberry Pi which means you only need one power supply for

this setup. Plug it in and wait for it to boot into the Screenly splash

screen. An IP address (of format http://aaa.bbb.ccc.ddd:8080)

should be displayed here, which will allow you to gain access to the

management dashboard.

03 Download Screenly OSE

Now that you have the hardware all ready to go we need

to download the Screenly OSE SD card image. This is only a 3.7GB

image file, however it may not fit on some 4GB SD cards so we

would recommend a minimum of 8GB, for extra space for all your

pictures and videos. Visit bit.ly/1wLKIRQ and download the ZIP file

from one of the mirrors under the “Getting started” heading.

02 Assemble your HDMIPi

The HDMIPi comes as a do-it-yourself kit rather than

a polished product. Not only does this make it cheaper for you

to buy, but it also gives it a more hack-like feel in its Pibow-

esque acrylic layer case. It is not hard to assemble, but in

case you get stuck there is a fantastic assembly video here:

http://hdmipi.com/instructions.

HDMIPi is a

collaboration

between Cyntech

and Alex Eames

from RasPi.TV. They

wanted to bring a

cheap HD resolution

HDMI screen to the

market that will

reduce the cost of

having a dedicated

monitor for your

Raspberry Pi. They

took to Kickstarter

to launch their idea

(kck.st/17zyaQg)

and there was a huge

response to this

project from both

within and outside

the Raspberry Pi

community. Over

2,500 people from

all over the world

enabled them to

smash their £55,000

target, and the

campaign ﬁ nished

with over £260,000.

UNICEF even

thought they were

good enough to use

in their educational

projects in Lebanon

(bit.ly/ZDpO8Z).

History of

HDMIPi

Above The reverse

view of HDMIPi,

showing GPIO and

connector cutouts

122 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

08 Disable Screenly video output

Load the IP displayed on the splash screen on the

browser of a different computer (you won’t be able to do it

directly from the same Pi). The Screenly OSE dashboard should

now load. Once inside the dashboard, move the slider for Big

Buck Bunny to the OFF position or delete the asset entirely.

09 Enter the command line

Once you have disabled the Big Buck Bunny

trailer from the web interface, you should now be able

to enter the command line easily and you can do this by

pressing Ctrl+Alt+F1 on the attached keyboard at any

time. Alternatively, you can access the command line

over SSH using the same IP address as shown previously

on the splash screen.

10 Run the update script

The image ﬁ le we downloaded from the website is

actually just a snapshot release and does not necessarily

include the latest Screenly OSE code, as the code updates

are made more regularly than the image. It is therefore

good practice to run an upgrade to the latest version using the

built-in script. You can run the following command:

~/screenly/misc/run_upgrade.sh

11 Conﬁ gure Raspberry Pi

Once you are successfully at the command line, you need

to type sudo raspi-config to enter the settings and then select

‘1 Expand root ﬁ le system’ to make sure you have access to all of

the space on the SD card. Then, change the time zone (option 4

and then 12) so that it is correct for your location. If your screen

has black borders around the edge you may also need to disable

overscan (option 8 and then A1). We would also recommend

changing the default password to something other than

raspberry to stop any would-be hackers from easily accessing

the Raspberry Pi via SSH (option 2). Once complete, exit without

restarting by selecting Finish and then No.

Above Screenly Pro

can manage multiple

screens and has

cloud storage too

12 Enable and set up Wi-Fi

As Screenly runs on top of Raspbian, the Wi-Fi setup

is essentially the same as the standard command line

setup within the OS. In order to do this you need to edit the

interfaces ﬁ le using sudo nano /etc/network/interfaces

and then type in the following code, replacing ssid and

password with the actual values:

auto lo



iface lo inet loopback

iface eth0 inet dhcp



allow-hotplug wlan0

auto wlan0



iface wlan0 inet dhcp

wpa-ssid “ssid”

wpa-psk “password”

iface default inet dhcp

Then exit and save by hitting Ctrl+X, then Y and then Return.

In this tutorial we

have used the open

source version

of Screenly –

Screenly OSE. This

is a fantastic bit

of software and a

great addition to

the open source

ecosystem. At this

point, some of you

may be dreaming

of huge remote-

managed display

screen networks

and the good news

is that this is entirely

possible with

Screenly Pro. This

is completely free

for a single display

screen and 2GB of

storage, and it has

larger packages for

purchase starting

at two screens right

up to 130+ screens.

It also adds a lot of

additional features

not seen in Screenly

OSE – ﬁ nd out more

about those on the

Screenly website

(bit.ly/1EXl92p).

Screenly

Pro Edition

Raspberry Pi Tips, Tricks & Hacks 123

16 Place in situ and enjoy!

Once you have got Screenly all set up and loaded all of

your favourite pictures and videos onto it via the web interface,

it is now time to enjoy the fruits of your labour! Mould the spider

stand (if you have one) into shape by taking the middle two legs

at the top and bending them downwards and backwards. Then

spread the front-middle legs a bit wider to give a good base and

shape the outer legs at the top and bottom to support the screen.

You are then ready to give it its permanent home – our expert’s is

on the mantelpiece over the ﬁ replace!

17 Other project ideas

In this tutorial we have looked at just one fairly basic

application of Screenly and the HDMIPi. You could use this

powerful open source software to run your digital signage empire,

share screens in schools and clubs, or as a personal dashboard

using a suitable web page. Whatever you make, please don’t forget

to take pictures and send them to us!

14 Upload pictures to Screenly

Once again, you will need to visit the Screenly OSE web

interface by entering the IP address into another computer.

Since you are now using a wireless connection, the IP address

may be different to the previous one. You need to select the

‘Add Asset’ option at the top right-hand side, which should

launch a pop-up options screen. Select Image from the drop-

down box and you then have the option of either uploading the

image or grabbing it from a URL using the corresponding tabs.

Enter the start date and end date of when this image should

appear, and how long it should appear on screen for, then press

Save. Repeat this step for each of the pictures.

15 Test with video and more

Pictures are great, but Screenly also allows you to display

videos (with audio if you wish) and web pages, which really is a

huge beneﬁ t. This is perfect if you want to enhance your digital

photo frame even further or perhaps display the local weather

and news to keep yourself informed. Plug in your speaker – we

would recommend The Pi Hut portable mini speaker (available

from bit.ly/1xEpBNZ) or anything similar.

Above Once fully conﬁ gured, load

your pictures and video to complete your

digital photo frame!

13 Test the connection

The easiest way to test the Wi-Fi connection is to shut

down the Raspberry Pi using sudo shutdown -h now and then

remove the wired network connection and reboot the Raspberry

Pi by removing and reattaching the microUSB power connector. If

the Wi-Fi connection has worked, you should now see the splash

screen with IP address again.

The default Screenly

image is essentially

some additional

software running

on top of Raspbian

OS. This means that

SSH is enabled by

default (it’s why we

changed the default

password in Step 11)

so it’s now possible

to access the

command line, as

well as the Screenly

dashboard, from

outside of your LAN.

We recommend

setting a static IP

for your Screenly-

powered Raspi

from your router

settings and then

setting up SSH with

keys on your Pi, and

port forwarding

on your router

for ports 22 and

8080. The Screenly

dashboard has no

can access it, but

an authentication

feature is imminent.

Access

Screenly

from afar

Tips | Tricks | Hacks

124 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

Games are a great way of understanding a

language: you have a goal to work towards, and

each feature you add brings more fun. However,

games need libraries and modules for graphics and

other essential games features. While the Pygame

library made it relatively easy to make games in

Python, it still brings in boilerplate code that you need

before you get started – barriers to you or your kids

getting started in coding.

Pygame Zero deals with all of this boilerplate code

for you, aiming to get you coding games instantly. Pg0

(as we’ll abbreviate it) makes sensible assumptions

about what you’ll need for a game – from the size of

the window to importing the game library – so that

you can get straight down to coding your ideas.

Pg0’s creator, Daniel Pope, told us that the

library “grew out of talking to teachers at Pycon

UK’s education track, and trying to understand

that they need to get immediate results and break

lessons into bite-size fragments, in order to keep a

whole class up to speed.”

To give you an idea of what’s involved, we’ll

build up a simple game from a

Pong

-type bat and

ball through to smashing blocks

Breakout

-style.

The project will illustrate what can be done with

very little effort. Pg0 is in early development but

still offers a great start – and is now included on

the Pi in the Raspbian Jessie image. We’ll look at

installation on other platforms, but ﬁ rst let’s see

what magic it can perform.

Pygame Zero cuts out the boilerplate to turn your ideas

into games instantly, and we’ll show you how

Pygame Zero cuts out the boilerplate to turn your ideas Pygame Zero cuts out the boilerplate to turn your ideas

What you’ll need

Q Pygame Zero

pygame-zero.readthedocs.org

Q Pygame

pygame.org

Q Pip

pip-installer.org

Q Python 3.2 or later

python.org

SCORE

0001200

LIVES BREAKOUT

Raspberry Pi Tips, Tricks & Hacks 125

Tips | Tricks | Hacks

01 Zero effort

Although game writing is not easy, getting started

certainly is. If you’ve got Raspbian Jessie installed on your Pi,

you’re ready to go. Open a terminal and type:

touch example.py

pgzrun example.py

And you’ll see an empty game window open (Ctrl+Q will close the

window). Yes, it’s that easy to get started!

04 No Pi?

You don’t even need a Raspberry Pi to install Pygame

Zero – just install the Pygame library, then use pip to install

Pygame Zero. Instructions vary by distro, but a good place to

start is the documentation: bit.ly/1GYznUB.

03 Older Raspbian

If you’re still running Raspbian Wheezy, you’ll need to run

the following steps to install Pygame Zero:

sudo apt-get update

sudo apt-get install python3-setuptools python3-pip

sudo pip-3.2 install pgzero

05 Intro.py

That default black square of 800 by 600 pixels we saw

in Step 1 can be overridden manually. For example, we can

replace it with an oversized gold brick, in a nod to

Breakout

WIDTH = 1000

HEIGHT = 100

def draw():

screen.fill((205, 130, 0))

That colour tuple takes RGB values, so you can quickly

get colours off a cheatsheet; screen is built into Pg0 for

the window display, with methods available for all sorts of

different sprites…

02 Python 3

If you haven’t got Raspbian Jessie, chances are you’ll

have neither Pg0 nor Pygame installed. The Python’s pip package

installer will take care of grabbing Pg0 for you, but the preceding

steps vary by distro. One thing you will need is Python 3.2 (or

newer). If you’ve been sticking with Python 2.x in your coding

(perhaps because it’s used in a tutorial you’re following), make

Pg0 your chance for a gentle upgrade to Python 3.

Pygame Zero deals with

all of this boilerplate code

for you, aiming to get you

coding games instantly

Right

Breakout

a classic arcade

game that can

be reimagined in

Pygame Zero

In situations where

Pygame is used

boilerplate and all

with young people,

great results can

also be achieved

(see Bryson Payne’s

book), but Pygame

and Pg0, despite

their use as powerful

educational tools,

are also good for

creating games for

coders no matter

what stage of

learning they are at.

Great games are all

about the gameplay,

driven by powerful

imaginations

generating images,

animations, sounds

and journeys

through game

worlds. Good

frameworks open

up this creative

activity to people

who are not

traditional learners

of programming,

which is an area

where Python has

long excelled.

Young

and old

Full code

FileSilo.co.uk

126 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

09 Mouse move

We want to move the bat, and the mouse is closer to an

arcade paddle than the arrow keys. Add the following:

def on_mouse_move(pos):

x, y = pos

bat.center = (x, bat.center[1])

Use pgzrun to test that you have a screen, bat and movement.

08 Batty

You can think of

Breakout

as essentially being a moving

bat – that is, you’re hitting a moving ball in order to knock out

blocks. The bat is a rectangle, and Pygame’s Rect objects store

and manipulate rectangular areas – we use Rect((left, top),

(width, height)), before which we deﬁne the bat colour and then

call upon the draw function to put the bat on the screen, using

the screen function.

W = 800

H = 600

RED = 200, 0, 0

bat = Rect((W/2, 0.96 * H), (150, 15))

def draw():

screen.clear()

screen.draw.filled_rect(bat, RED)

07 Breakout via Pong

While the Pi is something of a tribute to 1980s 8-bit

computers,

Breakout

comes from the 1970s and is a direct

descendant of the early arcade classic

Pong

. We’ll follow the

route from

Pong

Breakout

(which historically involved Apple

founders Steve Wozniak and Steve Jobs) in the steps to creating

our code, leaving you with the option of developing the

Pong

elements into a proper game, as well as reﬁning the ﬁnished

Breakout

clone.

06 Sprite

The intro example from the Pg0 docs expands on that

with the Actor class, which will automatically load the named

sprite (Pg0 will hunt around for a .jpg or .png in a subdirectory

called images).

alien = Actor(‘alien’)

alien.pos = 100, 56

WIDTH = 500

HEIGHT = alien.height + 20

def draw():

screen.clear()

alien.draw()

You can download the alien from the Pg0 documentation (bit.

ly/1Sm5lM7) and try out the animation shown there, but we’re

taking a different approach in our game.

Right The bat

and ball come

ﬁrst – they’re the

cornerstones of

Pong

and

Breakout

David Ames, who

uses Pg0 to teach

younger children

to code at events

across the UK, told

us: “One thing to

avoid when it comes

to teaching kids is

Object Orientation.”

OOP (object-oriented

programming) is

partly abstracted

away by Pg0, but it

can’t be ignored.

Perhaps the best

approach is using

Pg0 and some

simple code to start,

then dropping in a

piece of OO when it’s

needed to solve a

particular problem.

With the Code Club

age group – about

eight to eleven –

feeding information

to solve practical

problems works

well. It can work

with adults, too –

but there’s always

someone who’s read

ahead and has a few

tricky questions.

Object

orientation

Raspberry Pi Tips, Tricks & Hacks 127

Tips | Tricks | Hacks

10 Square ball

In properly retro graphics-style, we deﬁ ne a square

ball too – another rectangle, essentially, with the (30, 30) size

making it that subset of rectangles that we call a square.

We’re doing this because Rect is another built-in in Pg0. If we

wanted a circular ball, we’d have to deﬁ ne a class and then use

Pygame’s draw.ﬁ lled_circle(pos, radius, (r, g, b)) - but Rect we

can call directly. Simply add:

WHITE = 200,200,200

ball = Rect((W/2, H/2), (30, 30))

… to the initial variable assignments, and:

screen.draw.filled_rect(ball, WHITE)

… to the def draw() block.

12 def move(ball)

To get the ball to move within the screen we need to

deﬁ ne move(ball) for each case where the ball meets a wall. For

this we use if statements to reverse the ball’s direction at each

of the boundaries. Refer to the full code listing on page 67.

Note the hardcoded value of 781 for the width of screen,

minus the width of ball – it’s okay to hardcode values in

early versions of code, but it’s the kind of thing that will need

changing if your project expands. For example, a resizable

screen would need a value of W - 30.

13 Absolute values

You might expect multiplying y by minus one to work for

reversing the direction of the ball when it hits the bat:

ball_dir = Direction(ball_dir.x, -1 * ball_dir.y)

… but you actually need to use abs, which removes any minus

signs, then minus:

ball_dir = Direction(ball_dir.x, - abs(ball_dir.y))

Try it without in the ﬁ nished code and see if you get some

strange behaviour. Your homework is to work out why.

11 Action!

Now let’s make the ball move. Download the tutorial

resources in FileSilo.co.uk and then add the code inside the

‘move.py’ ﬁ le to assign movement and velocity. Change the 5 in

ball_dir = Direction(5, -5) if you want the ball slower or faster,

as your processor (and dexterity) demands – but it’s hard to

tell now because the ball goes straight off the screen! Pg0 will

call the update() function you deﬁ ne once per frame, giving the

illusion of smooth(ish) scrolling if you’re not running much else.

## Breakout type game to demonstrate Pygame Zero library

## Based originally upon Tim Viner’s London Python Dojo

## demonstration

## Licensed under MIT License - see file COPYING

from collections import namedtuple

import pygame

import sys

import time

W = 804

H = 600

RED = 200, 0, 0

WHITE = 200,200,200

GOLD = 205,145,0

ball = Rect((W/2, H/2), (30, 30))

Direction = namedtuple(‘Direction’, ‘x y’)

ball_dir = Direction(5, -5)

bat = Rect((W/2, 0.96 * H), (120, 15))

class Block(Rect):

def __init__(self, colour, rect):

Rect.__init__(self, rect)

self.colour = colour

blocks = []

for n_block in range(24):

block = Block(GOLD, ((((n_block % 8)* 100) + 2, ((n_block //

8) * 25) + 2), (96, 23)))

blocks.append(block)

def draw_blocks():

for block in blocks:

screen.draw.filled_rect(block, block.colour)

def draw():

screen.clear()

screen.draw.filled_rect(ball, WHITE)

screen.draw.filled_rect(bat, RED)

draw_blocks()

def on_mouse_move(pos):

x, y = pos

bat.center = (x, bat.center[1])

def on_mouse_down():

global ball_dir

ball_dir = Direction(ball_dir.x * 1.5, ball_dir.y * 1.5)

Full code listing

To get the ball to move we need to

deﬁ ne move(ball) for each case where

the ball meets a wall

128 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

19 Drawing blocks

Draw_blocks() is added to def draw() after deﬁning:

def draw_blocks():

for block in blocks:

screen.draw.filled_rect(block, block.colour)

20 Block bashing

All that remains with the blocks is to expand def

move(ball) – to destroy a block when the ball hits it.

to_kill = ball.collidelist(blocks)

if to_kill >= 0:

sounds.block.play()

ball_dir = Direction(ball_dir.x, abs(ball_dir.y))

blocks.pop(to_kill)

17 Going for gold

Create a Block class:

class Block(Rect):

def __init__(self, colour, rect):

Rect.__init__(self, rect)

self.colour = colour

… and pick a nice colour for your blocks:

GOLD = 205,145,0

18 Line up the blocks

This builds an array of 24 blocks, three rows of eight:

blocks = []

for n_block in range(24):

block = Bl o ck(G O LD, ((((n _ bl o c k % 8)* 100) + 2,

((n_block // 8) * 25) + 2), (96, 23)))

blocks.append(block)

16 Building blocks

There are many ways of deﬁning blocks and distributing

them onto the screen. In Tom Viner’s team’s version, from

the London Python Dojo – which was the code that originally

inspired this author to give this a go – the blocks are sized in

relation to number across the screen, thus:

N_BLOCKS = 8

BLOCK_W = W / N_BLOCKS

BLOCK_H = BLOCK_W / 4

BLOCK_COLOURS = RED, GREEN, BLUE

Using multicoloured blocks which are then built into an

array means that blocks can join without needing a border.

With its deﬁning variables in terms of screen width, it’s good

sustainable code, which will be easy to amend for different

screen sizes – see github.com/tomviner/breakout.

However, the array of colour bricks in a single row is not

enough for a full game screen, so we’re going to build our array

from hard-coded values…

15 Blockhead!

If you’re not very familiar with the ancient computer

game

Breakout

, then:

apt-get install lbreakout2

… and have a play. Now, we haven’t set our sights on building

something quite so ambitious in just these six pages, but we

do need blocks.

14 Sounds

Also upon bat collision, sounds.blip.play() looks in

the sounds subdirectory for a sound ﬁle called blip. You can

download the sounds (and ﬁnished code) from FileSilo.co.uk.

Actually, now we think about it, ignore the previous

comment about homework – your real homework is to turn

what we’ve written so far into a proper game of

Pong

! But ﬁrst

let’s ﬁnish turning it into

Breakout

Right Tom Viner’s

array of blocks

negates the need for

bordered rectangles

There’s a new

version of Pg0 in

development – it

may even be out

as you read this.

Pg0 creator Daniel

Pope tells us “a tone

generation API is in

the works,” and that

at the Pg0 PyConUK

sprint, “we ﬁnished

Actor rotation.”

Contributions are

welcome – not only

to the Pg0 code, but

more examples are

needed not just to

show what can be

done, but to give

teachers tools to

enthuse children

about the creative

act of programming.

Pg0 has also inspired

GPIO Zero, to make

GPIO programming

easier on the

Raspberry Pi, with

rapid development

occurring on this

new library as we go

to press.

Pg0 +1

Raspberry Pi Tips, Tricks & Hacks 129

Tips | Tricks | Hacks

22 Score draw

Taking advantage of some of Pygame Zero’s quickstart

features, we’ve a working game in around 60 lines of code.

From here, there’s more Pg0 to explore, but a look into Pygame

unmediated by the Pg0 wrapper is your next step but one.

First refactor the code; there’s plenty of room for

improvement – see the example ‘breakout-refactored.

py’ in your tutorial resources. Try adding scoring, the most

signiﬁ cant absence in the game. You could try using a global

variable and writing the score to the terminal with print(), or

instead use screen.blit to put it on the game screen. Future

versions of Pg0 might do more for easy score keeping.

23 Class of nine lives

For adding lives, more layers, and an easier life-

keeping score, you may be better deﬁ ning the class

GameClass and enclosing much of the changes you wish to

persist within it, such as self.score and self.level. You’ll ﬁ nd a

lot of Pygame code online doing this, but you can also ﬁ nd Pg0

examples, such as the excellent pi_lander example by Tim

Martin: github.com/timboe/pi_lander.

21 Game over

Lastly, we need to allow for the possibility of

successfully destroying all blocks.

if not blocks:

sounds.win.play()

print(“Winner!”)

time.sleep(1)

sys.exit()

24 Don’t stop here

This piece is aimed at beginners, so don’t expect to

understand everything! Change the code and see what works,

borrow code from elsewhere to add in, and read even more

code. Keep doing that, then try a project of your own – and let

us know how you get on.

def move(ball):

global ball_dir

ball.move_ip(ball_dir)

if ball.x > 781 or ball.x <= 0:

ball_dir = Direction(-1 * ball_dir.x, ball_dir.y)

if ball.y <= 0:

ball_dir = Direction(ball_dir.x, abs(ball_dir.y))

if ball.colliderect(bat):

sounds.blip.play()

ball_dir = Direction(ball_dir.x, - abs(ball_dir.y))

to_kill = ball.collidelist(blocks)

if to_kill >= 0:

sounds.block.play()

ball_dir = Direction(ball_dir.x, abs(ball_dir.y))

blocks.pop(to_kill)

if not blocks:

sounds.win.play()

print(“Winner!”)

time.sleep(1)

sys.exit()

if ball.y > H:

sounds.die.play()

print(“Loser!”)

time.sleep(1)

sys.exit()

def update():

move(ball)

Full code listing (co nt.)

Left Test your game

once it’s ﬁ nished

– then test other

people’s

Breakout

games to see how

the code differs

132 Build a Raspberry

Pi-controlled car

138 Raspberry Pi car computer 144

138

“Learn about the

technologies that are

starting to power the

world’s newest and

biggest economy”

150

132

146

Build a Raspberry

Pi-controlled car

Make use of cutting-edge web technologies to take control of a

remote controlled car with a smartphone or tablet…

Tips | Tricks | Hacks

132 Raspberry Pi Tips, Tricks & Hacks

Web technologies are moving forward at a huge pace, cloud

technologies are bringing mass computing to individuals,

and hardware has reached a perfect moment in time where

sensors, displays and wireless technology have all evolved

into efﬁ cient and affordable devices. We truly are at a point

where nearly anyone can take an idea from nothing to a working

product in a week and at very little cost. Just like this project,

which is fun, quick and easy to build on and a fantastic way to

learn. We’re going to grab an old remote-control car, rip off its

radio receiver and replace it with the Raspberry Pi, hook it up on

the network, ﬁ re up a bleeding-edge web server and then get

your smartphone or tablet to control it by tilting the device. By

the end of this, not only will you have a fun toy – you will have

learnt about the basic technologies that are starting to power

the world’s newest and biggest economy for the foreseeable

future. Welcome to tomorrow!

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 133

Tips | Tricks | Hacks

Components list

Q A toy RC car with two

channels (steering and drive)

Q Adafruit PWM I2C servo

driver

Q Female-to-female jumper

cables

Q 5V battery power bank

Components from

www.modmypi.com

Estimated cost: £60 / $100

Before you can take control of your car with a smartphone,

you’ll need to make some signiﬁ cant changes to the chassis

Raspberry Pi-controlled car build process

To help our toy car come to life using

the latest web technologies and our

credit card-sized computer, we’re

going to need to make some pretty

signiﬁ cant changes to its workings.

Fortunately, the most complex aspects

of the build can be accomplished with a

couple of affordable purchases, namely

a servo controller board to take care

of the steering and throttle, and a 5V

battery pack to keep the Raspberry Pi

running smoothly.

01 Identify and remove old radio

This project is effectively replacing the car’s normal

transmitter and receiver. Notice the three sockets on the original

receiver: one goes to the motor controller and one to the steering

servo. Some remote-control cars also have separate battery for

the electronics, but those (especially with an electronic speed

controller with BEC) get their 5V power supply directly from

the speed controller, saving on components. If you don’t have

a speed controller with 5V BEC, you’ll need to get a 5V supply

elsewhere. Many shops sell 5V battery power supplies – often as

mobile phone emergency top-ups. www.modmypi.com sells a

suitable 5V battery power bank for under £20.

Servo control We’ve used

the Adafruit PWM I2C servo driver

board from www.modmypi.com

Pi-powered The Raspberry

Pi sits front and centre to keep it

as safe as possible

Power up This 5V battery

pack keeps our Raspberry Pi

running for a good few hours

Pick a car You can use

pretty much any affordable

car for this project

134 Raspberry Pi Tips, Tricks & Hacks

Raspberry Pi Tips, Tricks & Hacks 135

Tips | Tricks | Hacks

We’re using the Raspberry Pi’s

I2C bus to control the servo

interface board

02 Attach the servo cables to

the new controller

We soldered our 16-channel I2C servo

controller board from www.modmypi.com

as per its instructions and simply plugged

channel 0 (steering) and channel 1 (motor)

headers onto it. There are six cables in

total: the bottom two are ground, the

middle two are the power and the top two

are the PWM (pulse-width modulation)

signals. This is a good time to think of

places to mount the extra components

and the best ﬁ xing method seems to be

sticky-back Velcro.

03 Connect the I2C bus to the

Raspberry Pi

We’re using the Raspberry Pi’s I2C bus

to control the servo interface board,

which only needs four cables – they all go

between the Raspberry Pi and the servo

controller board as pictured. This month’s

accelerometer tutorial explains how to set

up I2C on the Raspberry Pi.

From top to bottom we need to use the

1. GND, 2. SCL, 3. SDA and 4. VCC, which

map directly to the same ports on the

Raspberry Pi. Essentially this is power,

ground and two communication channels

– it’s all pretty straightforward so far…

04 Hooking it up to the

Raspberry Pi

On a Rev 1 Raspberry Pi, the cables look

the same. Though the Rev boards have

different labelling, the physical pins are

in the same place. Bottom left (closest

to the RasPi power connector) is the 3.3V

power; next to that is the SDA header,

05 Overview of the main

components

You should now have the servo board in

the middle with the steering servo and

speed controller on one side and the

Raspberry Pi on the other. The motor is

connected to the other end of the speed

controller (that end should have much

thicker wires); the speed controller

also has two thick wires going to the

main car’s battery – in this case a 7.2V

NiCad. We now have two very separate

power systems with the high current

motors on one side and the low current

electronics on the other. Let’s make

sure it stays that way!

06 Find everything a home

Now it’s time to ﬁ nd a home

for the new components. Use plenty of

sticky-back Velcro, tie wraps or elastic

bands to keep everything secure and

ﬁ nd spaces in the car’s body to hide the

wires where possible. While it is possible

to stick or screw the Raspberry Pi directly

to the car, we recommend to use at least

the bottom half of a case for added

protection and ease of access. Insert your

SD card, network cable or Wi-Fi dongle (if

programming from another machine) and

power supply. Sit back and admire your

hacking. Next we’ll tackle the software

side of the project…

which is the data channel. Next to that

in the bottom right is the SCL channel,

which controls the clock of the I2C

devices. And ﬁ nally – on the top-right port

– is the Ground.

Step 02

Step 03

Step 05

Step 06

Tips | Tricks | Hacks

What you’ll need

Q A RasPi car, ready to go

Q An internet connection

Q A reasonably modern

smartphone/tablet

Q Pi car source code

github.com/shaunuk/picar

Control a toy car with a smartphone and the latest web technologies

Controlling your Raspberry Pi-powered car

Now we have our fantastic Raspberry

Pi-powered car all wired and charged,

it’s time to make it come alive. We’re

using the best web technologies

that the JavaScript programming

language offers, to harness the natural

movement of your hand and wirelessly

drive the vehicle. Each little movement

will trigger an event that calculates

what the car should do and then sends

it over a socket connection up to 20

times a second.

01 Download and install

the software

To get the I2C connectivity working,

you can follow the steps from pages

64-65. Next we’ll need to ﬁ nd a home

for our new project code – how about /

var/www/picar? Type sudo mkdir /

var/www/picar in the terminal to make

the directory and then change into that

directory: cd /var/www/picar.

Now, to download the project using

Git, type sudo git clone http://

github.com/shaunuk/picar

. If you

haven’t got Git, install it with sudo apt-

get install git.

This will download the custom

software for driving the car, but we still

need the web server and some other bits

before we can start burning rubber…

02 Download and install

Node.js

We now need to get the awesome Node.

js and its package tool, the Node package

manager (npm). Type sudo wget http://

nodejs.org/dist/v0.10.21/node-

v0.10.21-linux-arm-pi.tar.gz. This

will download a fairly recent version of

Node.js – the version Raspbian has in

its repositories is way too old and just

03 Conﬁ gure Node.js

To make it easy to run from

everywhere, we will create symbolic

links for Node and npm binaries. In the

terminal, type sudo ln -s /var/www/

node-v0.10.21-linux-arm-pi/bin/

node /bin/node and then sudo ln

-s /var/www/node-v0.10.21-linux-

arm-pi/bin/npm /bin/npm. Then,

to get the extra modules, type npm

install socket.io node-static

socket.io adafruit-i2c-pwm-driver

sleep optimist

04 Get to know the project

Now we have everything, you

should see three ﬁ les: the server (app.js),

the client (socket.html) and the jQuery

JavaScript library for the client. The

server not only drives the servos, but it

is a web server and sends the socket.

html ﬁ le and jQuery to the browser when

requested – it’s a really neat and simple

setup and just right for what we’re trying

to achieve.

05 Test the servos

Our handy little program (app.js) has a special mode

just for testing. We use two keywords here: beta for servo 0

(steering) and gamma for servo 1 (motor control). Type node

app.js beta=300. You should see the front wheels turn. Now the

numbers need experimenting with. On our example, 340 was left,

400 was centre and 470 was right. Do the same for the motor by

typing node app.js gamma=400 and take note of the various

limits of your car.

06 Conﬁ gure sensible defaults

Now you know what your car is capable of, we

can set the defaults in app.js and socket.html. Edit app.js

and ﬁ nd the section that says ‘function emergencyStop’.

Adjust the two numbers to your car’s rest values. Then open

socket.html and adjust the predeﬁ ned values under ‘Deﬁ ne

your variables here’.

07 Going for a spin

We’re almost ready to try it out, but you need to know the

IP address of your Pi car, so type ifconfig at the terminal. Then

ﬁ re up the app by typing node app.js. Now grab the nearest

smartphone or tablet, making sure it’s on the same network

as your Pi. Open the web browser and go to http://[your IP

address]:8080/socket.html. You should get an alert message

saying ‘ready’ and as soon as you hit OK, the gyro data from your

phone will be sent to the car and you’re off!

Above You need to adjust some of the variables to control your

particular remote controlled car set-up

doesn’t work with the new technologies

we’re about to use. Extract the node

package by typing sudo tar -xvzf

node-v0.10.21-linux-arm-pi.tar.gz.

Step 05

Step 07 Below All you need to ﬁ nish off your project is

access to a smartphone or tablet

Raspberry Pi Tips, Tricks & Hacks 137

Tips | Tricks | Hacks

socket.html

<html>

<head>

script>

scale=1.0, maximum-scale=1.0;” />

//------ Define your variables here

var socket = io.connect(window.location.hostname+’:8080’);

var centerbeta = 400; //where is the middle?

var minbeta = ‘34 0’; //right limit

var maxbeta = ‘470’; //l e ft lim it

var multbeta = 3; //factor to multiply the raw gyro figure 

by to get the desired range of steering

var centergamma = 330;

var ajustmentgamma = 70; //what do we do to the angle to get

to 0?

var mingamma = 250; //backwards limit

var maxgamma = 400; //forward limit

var multgamma = 1; //factor to multiply the raw gyro figure 

by to get the desired rate of acceleration

window.la stbeta =’0’;

window.la stg a m m a =’0’;

$(function(){

window.gyro = ‘rea d y’;

alert(‘Ready -- Lets race !’);

});

window.ondeviceorientation = function(event) {

beta = centerbeta+(Math.round(event.beta*-1)*multbeta);

if (beta >= maxbeta) {

beta=maxbeta;

}

if (beta <= minbeta) {

beta=minbeta;

}

gamma = event.gamma;

gamma = ((Math.round(event.gamma)+ajustmentgamma)* 

multgamma)+ centergamma;

//stop sending the same command more than once

send = ‘N’;

if (window.lastbeta != beta) { send = ‘Y’ }

if (window.lastgamma != gamma) { send = ‘Y’ }

window.la stbeta = beta;

window.lastgamma=gamma;

if (window.gyro == ‘ready’ && send==’Y’) { //don’t send 

another command until ready...

window.gyro = ‘notready’;

socket.emit(‘fro mclient’, { beta: beta, gamma: gamma } );

window.gyro = ‘rea d y’; }}

app.js

//declare required modules

var app = require(‘http’).createServer(handler)

, io = require(‘s o c ket.io’).l i s t e n (a p p)

, fs = require(‘fs’)

, static = require(‘node-static’)

, sys = require(‘sys’)

, PwmDriver = require(

‘a dafr uit-i2c-p w m -d river’)

, sleep = require(‘sleep’)

, argv = require(‘o ptimist’).a r g v;

app.listen(8080);

//set the address and device name of the 

breakout board

pwm = new PwmDriver(0x40,’/ d e v / i 2 c - 0 ’ );

//set pulse widths

setServoPulse = function(channel, pulse) {

var pulseLength;

pulseLength = 1000000;

pulseLength /= 60;

print(“%d us per period” % pulseLength);

pulseLength /= 4096;

print(“%d us per bit” % pulseLength);

pulse *= 1000;

pulse /= pulseLength;

return pwm.setPWM(channel, 0, pulse);

};

//set pulse frequency

pwm.setPWMFreq(60);

//Make a web server on port 8080

var file = new(static.Server)();

function handler(request, response) {

console.log(‘ser ving file’,re q u est.url)

file.serve(request, response);

};

console.log(‘Pi Car we server listening on port 8080 visit 

http://ipaddress:8080/socket.html’);

lastAction = “”;

function emergencyStop(){

pwm.setPWM(0, 0, 400); //center front wheels

pwm.setPWM(1, 0, 330); //s t o p m o to r

console.log(‘###EMERGENCY STOP - signal lost or shutting 

down’);

}

if (argv.beta) {

console.log(“\nPerforming one off servo position move 

to: “+argv.beta);

pwm.setPWM(0, 0, argv.beta); //using direct i2c pwm module

pwm.stop();

return process.exit();

}

if (argv.gamma) {

console.log(“\nPerforming one off servo position move 

to: “+argv.gamma);

pwm.setPWM(1, 0, argv.gamma); //using direct i2c pwm module

pwm.stop();

return process.exit();

}

//fire up a web socket server

io.sockets.on(‘co nnectio n’, function (socket) {

socket.on(‘fromclient’, function (data) {

console.log(“Beta: “+data.beta+” Gamma: “+data.gamma);

//exec(“echo ‘sa “+data+”’ > /dev/ttyAMA0”, puts); //using 

http://electronics.chroma.se/rpisb.php

//exec(“picar.py 0 “+data.beta, puts); //using python 

adafruit module

pwm.setPWM(0, 0, data.beta); //using direct i2c pwm module

pwm.setPWM(1, 0, data.gamma); //using direct i2c pwm module

clearInterval(lastAction); //stop emergency stop timer

lastAction = setInterval(emergencyStop,1000); //s e t 

emergency stop timer for 1 second

});

process.on(‘SIGINT’, function() {

emergencyStop();

console.log(“\nGracefully shutting down from SIGINT 

(Ctrl-C)”);

pwm.stop();

return process.exit();

});

We’ll harness the natural movement of your

hand and wirelessly drive the vehicle

Full code listing

138 Raspberry Pi Tips, Tricks, & Hacks

Cars are getting clever. These days, with smart

navigation interfaces built into new cars, you

don’t need to go out and buy yourself a TomTom

to get help with directions. But if you’ve got a

Raspberry Pi then you don’t even need to buy that – let alone a

new car!

In this project we will show you how to build your own car

computer with your Pi, a quality touchscreen like the 9-inch model

from SainSmart that we’re using here, and a few other bits like a

GPS module and USB 3G modem. Your CarPi will be able to use

open source navigation software Navit to show your route map

on screen, plus speech synthesis to read out directions, and it will

also be able to check your location and give you weather reports.

It’ll work as a music player too, of course.

It’s an ambitious project, but you will gain a solid understanding

of custom-made interfaces, navigation software and geolocation

data, touchscreen calibration, speech synthesis and more.

While you don’t have to use the same SainSmart screen as us,

we do recommend it for this project as it is one of the few large

touchscreens out there for the Pi. There are more improvements

at the end too, so check the components list, make sure you’ve got

everything and let’s get started!

Raspberry Pi

Car Computer

Make your own touchscreen navigation

system that gives directions, local

weather reports and plays music

Raspberry Pi Tips, Tricks & Hacks 139

Tips | Tricks | Hacks

140 Raspberry Pi Tips, Tricks, & Hacks

01 Basic conﬁ guration

Boot up your Raspberry Pi and expand the ﬁ lesystem

using raspi-conﬁ g. Go to Advanced Options and disable the

Serial connection – you’ll need this to talk to the GPS module

later. In raspi-conﬁ g, enable X at boot as the pi user. Say Yes to

reboot. Once rebooted, ensure your packages are up to date with:

sudo apt-get update

sudo apt-get upgrade

04 Connect the screen

The SainSmart screen doesn’t come with any written

instructions. Instead there is a YouTube video on their website

with details about how to put it together: bit.ly/1DF6eJJ. The

important part is that the DC power supply should be 12V.

03 Install navigation software

Begin to install the Navit navigation software by entering:

sudo apt-get install navit gpsd gpsd-clients espeak

sudo nano /etc/default/gpsd

set START_DAEMON=“true”

…and set:

DEVICES=”/dev/ttyAMA0”

Start the GPS daemon with:

sudo /etc/init.d/gpsd start

You can check it’s working by looking at the GPS data with:

cgps -s

02 Connect GPS module

Solder the pin headers onto the Adafruit GPS module.

You can also solder the battery connector which is used to keep

the device partially active, giving a faster ﬁ x. You only need to use

4 pins: 3.3V, ground, serial transmit and serial receive. Power the

Pi off again before connecting anything.

As we are using GPS, the antenna will have to go outside or

under a window to gain signal. Connect the antenna to the board

and power everything back on. The light on the GPS module will

ﬂ ash frequently while ﬁ nding a ﬁ x. Once it has one, it will blink

every 15 seconds.

05 Set the screen resolution

We will have to force the correct resolution (1024x600)

for the screen by editing /boot/conﬁ g.txt with sudo. To do so,

add the following options:

framebuffer_width=1024

framebuffer_height=600

hdmi_force_hotplug=1

hdmi_cvt=1024 600 60 3 0 0 0

hdmi_group=2

hdmi_mode=87

For the changes to properly take effect you will need to reboot

with sudo reboot.

06 Download kernel source

To start the touchscreen, you need to compile an

extra kernel module to support it. The program rpi-source

(github.com/notro/rpi-source/wiki) will ﬁ nd the source of

your kernel. Install rpi-source with:

sudo wget https://raw.githubusercontent.com/notro/

rpi-source/master/rpi-source -O usr/bin/rpi-source

&& sudo chmod +x /usr/bin/rpi-source && /usr/bin/

rpi-source -q -tag-update

Then run rpi-source to get the source of the running kernel.

Above We’re using

Adafruit’s excellent

GPS Breakout kit

here: bit.ly/1G8X2gw

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 141

#!/usr/bin/env python2

import os, sys, requests, pygame

from gps import *

from pygame.locals import *

class WeatherClient:

apikey = “7232a1f6857090f33b9d1c7a74721”

@staticmethod

def latlon():

gpsd = gps(mode=WATCH_ENABLE)

# Needs better error handling

try:

while True:

report = gpsd.next()

if report[‘class’] == ‘TPV’:

gpsd.close()

return report[‘lat’], report[‘lon’]

except:

return None, None

@staticmethod

def usefuldata(j):

# Returns a string of useful weather data from a LOT of json

d = j[‘data’][‘current_condition’][0]

out = “Now - Temp: {0}C, Feels Like: {1}C, Description: {2}\n”\

.format(d[‘temp_C’],

d[‘FeelsLikeC’],

d[‘weatherDesc’][0][‘value’])

hourly = j[‘data’][‘weather’][0][‘hourly’]

hour_count = 1

for h in hourly:

out += (“+{0}hr - Temp: {1}C, Feels Like: {2}C, Chance of Rain:”

“ {3}%, Description: {4}\n”)\

.format(hour_count,

h[‘tempC’],

h[‘FeelsLikeC’],

h[‘chanceofrain’],

h[‘weatherDesc’][0][‘value’])

hour_count += 1

# Rstrip removes trailing newline

return out.rstrip()

@staticmethod

def update():

errstr = “Error getting weather data”

lat, lon = WeatherClient.latlon()

if lat == None or lon == None:

return errstr

api_req = (“http://api.worldweatheronline.com/free/v2/weather.ashx”

“?q={0}%2C{1}&format=json&key={2}”).format(lat, lon,

WeatherClient.apikey)

r = None

Full code listing

07 Update GCC

Recent Raspberry Pi kernels are

compiled with GCC 4.8. Raspbian only

comes with 4.6 so you will have to install

4.8 to continue with the following steps.

Do this by entering:

sudo apt-get install -y gcc-4.8

g++-4.8 ncurses-dev

Then you have to set GCC 4.8 as

the default:

sudo update-alternatives

--install /usr/bin/gcc gcc /usr/

bin/gcc-4.6 20

sudo update-alternatives

--install /usr/bin/gcc gcc /usr/

bin/gcc-4.8 50

sudo update-alternatives

--install /usr/bin/g++ g++ /usr/

bin/g++-4.6 20

sudo update-alternatives

--install /usr/bin/g++ g++ /usr/

bin/g++-4.8 50

08 Pick the module to compile

Rpi-source puts the kernel

source in a folder called ‘linux’. To

choose the USB Touchscreen Driver,

enter the following:

cd linux

make menuconfig

Device Drivers -> Input device

support -> Generic input layer

(needed for keyboard, mouse,

…) -> Touchscreens (press space

to include) -> USB Touchscreen

Driver (press M to make module)

Once you’ve done that, you then need

to make sure you save your changes as

‘.conﬁ g’ and run scripts/diffconﬁ g to see

the differences.

09 Compile and install

the module

Now you need to compile and install the

module. Do so by entering:

make prepare

make SUBDIRS=drivers/input/

touchscreen modules

sudo make SUBDIRS=drivers/input/

touchscreen modules_install

sudo depmod

If you unplug and reconnect the

touchscreen, it should work ﬁ ne but it

will probably need calibrating.

Tips | Tricks | Hacks

142 Raspberry Pi Tips, Tricks & Hacks

10 Calibrate the touchscreen

At this point, you can easily calibrate the touchscreen by

entering the following:

cd /etc/X11

sudo mkdir xorg.conf.d

cd xorg.conf.d

sudo nano 99-calibration.conf

…with the following content:

Section “InputClass”

Identifier “calibration”

MatchProduct “eGalax Inc. USB TouchController”

Option “SwapAxes” “1”

Option “InvertX” “1”

EndSection

Invert X actually inverts Y because the axes have been swapped

around. Reboot again for these changes to occur. Now the

calibration is roughly correct, download an input calibrator that

Adafruit have packaged already.

wget http://adafruit-download.s3.amazonaws.com/

xinput-calibrator_0.7.5-1_armhf.deb

sudo dpkg -i xinput-calibrator_0.7.5-1_armhf.deb

DISPLAY=:0.0 xinput_calibrator

DISPLAY=:0.0 is useful because you can run the program from

any terminal (including an SSH session) and have it appear on

the touchscreen. Touch the points on the screen as prompted.

Once the program is ﬁ nished, you should get an output that is

similar to the following:

Option “Calibration” “84 1957 270 1830”

Add it to the ‘99-calibration.conf’ ﬁ le that we created earlier

just below the other Option entries.

11 Download maps

Navit needs maps; download them from maps.navit-

project.org. You can either use the web browser on the Pi or

download the map from another machine and copy it using

scp. Use the predeﬁ ned area option to select where you live.

The smaller the area that you pick, the less data you will have to

process. Here the UK has a map size of 608 MB. Now move the

map to the navit folder:

mkdir -p /home/pi/.navit/maps

mv /home/pi/Downloads/$your_map /home/pi/.

navit/$country.bin

For example:

mv /home/pi/Downloads/osm_bbox_-9.7,49.6,2.2,61.2.bin

/home/pi/.navit/maps/UK.bin

12 Navit conﬁ guration

Sudo-edit /etc/navit/navit.xml with your favourite

editor. Search for openstreetmaps. Now disable the sample

map above, enable the openstreetmap mapset and set the

data variable to where you just moved your map. In this case

it looks like this:

<map type=“binfile” enabled=“yes” data=“/home/

pi/.navit/maps/UK.bin”/>

</mapset>

Then search for osd entries similar to:

…and enable the ones you want – we recommend enabling

them all. You may want to zoom in closer than the default map

layout. A zoom value of 64 is useful.

We’ve looked at

the PiTFT and the

HDMIPi before,

but the SainSmart

touchscreen

we’re using here is

uniquely suited to

many embedded

projects. It’s larger

than the PiTFT but

also without the

large bezels of the

HDMIPi – and it’s

incredibly thin –so

it’s the kind of thing

that is really useful

for installation

projects, whether

that’s something as

simple as a photo

slideshow in a real

picture frame or a

home automation

control interface

embedded into a

cupboard door.

Embed

the screen

SainSmart’s

9-inch HDMI/VGA

touchscreen (bit.

ly/1Ciu4H9) has a

fantastic display

and is perfect

for all sorts of

Pi projects

The screen

control panel that

comes with the

SainSmart screen

enables you to

easily change the

display settings

(i.e. brightness,

contrast, etc) as

well as the input

(i.e. HDMI, VGA,

AV1, etc)

As well as the main

controller board,

the touch screen

is connected to

a four-line USB

controller which

then plugs into the

Pi’s USB port

Adafruit’s Ultimate

GPS Breakout kit

provides Navit

and the weather

function with the

location data that

they require

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 143

13 Sound conﬁ guration

Before conﬁ guring speech

support for Navit, conﬁ gure the external

sound card. You have to stop the

Broadcom module from loading and

remove some Raspberry Pi-speciﬁ c ALSA

(Advanced Linux Sound Architecture).

To do this, sudo-edit /etc/modprobe and

comment out (i.e. preﬁ x with a #):

snd-bcm2835

Then run:

sudo rm /etc/modprobe.d/alsa*

Reboot for the changes to take effect.

Use alsamixer to set the volume on the

if it’s too quiet.

15 Create speech script

Navit supports speech by

running an external script and passing

the text to speak as an argument.

Create one using:

cd /home/pi/.navit

wget http://liamfraser.co.uk/

lud/carpi/chime.wav

touch speech.sh

chmod +x speech.sh

Now edit speech.sh:

#!/bin/bash

aplay -r 44100 /home/pi/.navit/

chime.wav

espeak -vmb-en1 -s 110 -a 150

-p 50 “$1”

Finally, test it with:

./speech.sh “Hello World”

14 Download a voice

The speech synthesis software

needs a voice and a proprietary

binary. You can get both by completing

the following steps:

sudo mkdir -p /usr/share/

mbrola/voices/

wget http://www.tcts.fpms.ac.be/

synthesis/m brola/dba/en1/en1-

980910.zip

unzip en1-980910.zip

sudo cp en1/en1 /usr/share/

mbrola/voices

wget http://www.tcts.fpms.ac.be/

synthesis/mbrola/bin/raspberri_

pi/mbrola.tgz

tar zxvf mbrola.tgz

sudo mv mbrola /usr/local/bin/

try:

r = requests.get(api_req)

except requests.exceptions.RequestException as e:

return errstr

return WeatherClient.usefuldata(r.json())

class CarLauncher:

def __init__(self):

pygame.init()

pygame.mixer.quit() # Don’t need sound

screen_info = pygame.display.Info()

self.screen = pygame.display.set_mode((screen_info.current_w,

screen_info.current_h))

pygame.display.set_caption(‘Car Launcher’)

self.titlefont = pygame.font.Font(None, 100)

self.wfont = pygame.font.Font(None, 30)

self.w_text = None # Weather text

def clean_background(self):

background = pygame.Surface(self.screen.get_size())

self.background = background.convert()

self.background.fill((0, 0, 0))

# Render title centered

text = self.titlefont.render(“CarPi Launcher”, 1, (255, 255, 255))

textpos = text.get_rect()

textpos.centerx = self.background.get_rect().centerx

self.background.blit(text, textpos)

self.screen.blit(self.background, (0,0))

pygame.display.flip()

def main_menu(self):

# btns maps Text -> Rectangles we can do collision detection on

self.btns = {‘Music’ : None, ‘NAV’ : None, ‘Weather’ : None}

item_num = 1

for key in self.btns:

text = self.titlefont.render(key, 1, (255,255,255))

textpos = text.get_rect()

max_width = self.background.get_rect().width / len(self.btns)

center_offset = max_width * 0.5

# This y pos puts buttons just below title

textpos.centery = self.background.get_rect().centery / 2

textpos.centerx = (max_width * item_num) - center_offset

self.btns[key] = textpos

self.screen.blit(text, textpos)

item_num += 1

pygame.display.flip()

def select_rect(self, rect, text):

# Colour a rect the user has clicked in green

surface = pygame.Surface((rect.w, rect.h))

surface.fill((0, 255, 0))

# Now we have to draw the text over it again

t = self.titlefont.render(text, 1, (255,255,255))

surface.blit(t, (0,0))

self.screen.blit(surface, rect)

pygame.display.flip()

Full code listing

Tips | Tricks | Hacks

144 Raspberry Pi Tips, Tricks & Hacks

You will need to write your

own launcher for CarPi

17 Install the music player

MPD is the music player back-end and pympdtouchgui

is the front-end that needs installing manually:

sudo apt-get install mpd ncmpcpp

wget http://www.spida.net/projects/software/

pym pdtouchg ui/py mp dto uchgui-0.320.tgz

tar zxvf pympdtouchgui-0.320.tgz

cd pym pdtouch g ui-0.320/

sudo python setup.py install

# Fix hard coded path in software

sudo ln -s /usr/local/share/pympdtouchgui/ /usr/

share/pympdtouchgui

run sudo passwd to set a password for root. From a computer

with music on, run:

scp -r music_folder root@pi_ip_address:/var/lib/

mpd/music/

Then on the Pi, change the ownership of the music that

you just copied:

sudo chown -R mpd:audio /var/lib/mpd/music

20 Install awesome window manager

Now you will need to write your own launcher for

CarPi, which will run full-screen. To ensure every application

is forced to full-screen, use awesome window manager in full-

screen mode.

sudo apt-get install awesome

sudo rm /etc/alternatives/x-session-manager

sudo ln -s /usr/bin/awesome /etc/alternatives/x-

session-manager

When changing the default x-session-manager, awesome will

be auto-started at boot instead of LXDE. If you reboot the Pi,

awesome should then load up automatically.

19 Update mpd music library

Ncmpcpp is a command line client for mpd. Type

ncmpcpp and press U to update the library. Press 3 to

browse the library and check the music is there, and press

Q to quit. Pressing 1 will select the help screen if you want

to do more.

16 Conﬁ gure Navit for speech

The last part is simple. Edit the Navit conﬁ g ﬁ le again (/

etc/navit/navit.xml) and replace the following line:

<speech type=“cmdline” data=“echo ‘Fix the speech

tag in navit.xml to let navit say:’ ‘%s’” cps=“15”/>

…with:

<speech type=“cmdline” data=“/home/pi/.navit/

speech.sh %s” cps=“10” />

Now you can run Navit with DISPLAY=:0.0 navit and have

fun experimenting.

18 Copy music

Scp (secure copy protocol) was used here to copy

music. First get the Pi’s IP address by running ip addr. Then

It is deﬁ nitely best

to put this project

together in a clean

workspace so that

you can clearly

see what you’re

working with and

ensure everything is

correctly wired and

soldered, but the

point of the project

is to make this setup

portable so that you

can put it in your

car and use it on

the road. You could

install everything

into a single, hand-

made enclosure or

customise a large

bought one, or you

could secure the

various parts inside,

for example, your

glovebox or car

doors. You’ll also

need to power both

the screen and your

Pi with a power pack

and ensure that

the GPS antenna is

fastened into a good

spot for signal.

Make it

mobile

Above The pympdtouchgui front-end for the

music player is surprisingly featureful

Above The Navit software comes with a host

of options built into its menu hierarchy

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 145

def reset(self):

self.clean_background()

self.main_menu()

self.render_weather()

def execute(self, path):

os.system(path)

# os.system blocks so by the time we get here application

# has finished

self.reset()

def render_weather(self):

if self.w_text == None:

return

# Get y starting at the bottom of the nav button

margin = 10

y = self.btns[‘NAV’].bottomleft[1] + margin

for t in self.w_text.split(“\n”):

line = self.wfont.render(t.rstrip(), 1, (255,255,255))

line_rect = line.get_rect()

line_rect.centerx = self.background.get_rect().centerx

line_rect.y = y

self.screen.blit(line, line_rect)

y += margin + line_rect.height

pygame.display.flip()

def handle_events(self, events):

for e in events:

if e.type == QUIT:

sys.exit()

elif e.type == MOUSEBUTTONDOWN:

pos = pygame.mouse.get_pos()

# Check if it collides with any of the buttons

for btn_text, rect in self.btns.iteritems():

if rect.collidepoint(pos):

self.select_rect(rect, btn_text)

if btn_text == “NAV”:

self.execute(“/usr/bin/navit”)

elif btn_text == “Music”:

self.execute(“/usr/local/bin/pympdtouchgui”)

elif btn_text == “Weather”:

self.w_text = WeatherClient.update()

# Reset will render weather if string is populated

self.reset()

def loop(self):

clock = pygame.time.Clock()

self.reset()

while 1:

self.handle_events(pygame.event.get())

# 5 fps is plenty

clock.tick(5)

if __name__ == “__main__”:

cl = CarLauncher()

cl.loop()

Full code listing

21 Install the requirements

for your launcher

The launcher is going to use a weather

API combined with location data

from the GPS receiver to give weather

updates when requested. The nicest

HTTP API for Python is requests, which

you can install by doing the following:

sudo apt-get install python-pip

sudo pip install requests

23 Start the launcher

automatically

Sudo-edit /etc/xdg/awesome/rc.lua and

move awful.layout.suit.max.fullscreen

to the top of the layouts list. Add the

following to the bottom of the ﬁ le:

awful.util.spawn_with_shell(“/

home/pi/carlauncher/carlauncher.

py”)

Now reboot again and the launcher

should come up automatically.

24 Future improvements

There are a number of

improvements that could be made

to the base project at this point:

• Make the launcher switch between

applications rather than start them

again each time

• Make the launcher look better

aesthetically with icons

• Use Mopidy instead of MPD so you

can use Spotify

• Further Navit conﬁ guration to make

it more featureful

• An SSD or USB ﬂ ash drive for storage

to make things quicker

22 Write the launcher code

Creating the code itself is pretty

self explanatory, but you can use our

ready-made version by downloading the

CarPi package from FileSilo.co.uk and

extracting carlauncher/carlauncher.py.

Tips | Tricks | Hacks

Create a piece of wearable tech with power moves

assigned to each button to enhance your Minecraft game

Build a Minecraft

power move glove

Many of you will be avid fans of the game

Minecraft

. In

schools it is fast becoming a motivational teaching and

learning tool, useful in areas such as programming, creating

logic gates and setting up a network.

This project is framed around creating a simple networked

Minecraft

game where one player chases the other and

tries to hit the block they are standing on. The real hack is

programming a ‘power glove’ that enables you to assign power

moves to each button. These powers can then be deployed

and used to slow down the other player and get yourself out

of sticky situations – check out the video at bit.ly/1CQSmHS!

The real beauty of this hack is that you can then create and

customise your own power moves. The possibilities are

endless, limited only by your imagination. If you’re conﬁ dent

with GPIO pins and setting up buttons, jump straight to Step 8.

01 Update the Raspberry Pi

This project is designed for the Raspberry Pi 2 which

requires the updated operating system, although it is compatible

with the Raspberry Pi B+ too. First ensure that the software is up

to date – open the LX Terminal type:

sudo apt-get update

sudo apt-get dist-upgrade

sudo apt-get install raspberrypi-ui-mods

02 Connect a button to the Raspberry Pi

Take one of the buttons and connect a wire to each

contact, then take the other two ends and connect to the Pi. You

may ﬁ nd this easier using a female-to-female connector. To set

up a test button, use GPIO pin 17 – this is physical pin number 11

on the board. The other wire connects to a ground pin, shown by a

minus sign (the pin above GPIO pin 17 is a ground pin).

What you’ll need

Q Raspberry Pi 2

Q 4 x 6mm tactile buttons

Q Female-to-female jerky

Q Terminal blocks

Q A glove

Q Router

Q 2x CAT5 cables

Raspberry Pi Tips, Tricks & Hacks 147

Tips | Tricks | Hacks

05 Open Minecraft

The updated version of the Raspbian OS comes with

Minecraft

pre-installed, it can be found under Menu>Games

– so load it up. If you have used the

Minecraft: Pi Edition

before

you will be aware that it runs better in a smaller-sized window,

so don’t make it full screen. You may prefer to adjust and arrange

each window side-by-side to enable you to view both the Python

code and the

Minecraft

game at the same time.

03 Test that the button works

Use this test code to ensure the button is functioning

correctly. Once it is, the same setup method can be used

throughout this project. To ensure the buttons are responsive,

use the pull-up resistor with the code GPIO.PUD_UP – this will

ensure that multiple touches aren’t registered on each button.

Using Python 2.8, type in the code below, then save and run. If

working correctly, it will return the message ‘Button works’.

import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BCM)

GPIO.cleanup()

GPIO.setup(17, GPIO.IN, GPIO.PUD_UP)

while True:

if GPIO.input(17) == 0:

print “Button works”

04 Create a power move

Now to create your ﬁ rst power move. The glove and code

are structured in such a way that once the basic code template is

set up, you can create your own power moves and assign them to

each button, keeping both your ideas and your gameplay fresh.

The ﬁ rst power move you will program enables you to place a wall

of TNT between you and the player trying to catch you. They have

a choice to go around the wall or blow it up, but it will slow them

down. In a new Python window, type the code below and save the

program into the home folder:

import time

def Firewall():

mc.postToChat(“Firewall Placed”)

TNT = 46,1

x, y, z = mc.player.getPos()

mc.setBlocks(x-6, y, z+2, x+6, y+10, z+3, TNT)

time.sleep(10)

while True:

Firewall()

import time

from mcpi import minecraft

mc = minecraft.Minecraft.create(“192.168.1.211”)

#Replace with the other players IP address

import RPi.GPIO as GPIO

#Set up the GPIO Pins

GPIO.setmode(GPIO.BCM)

#Sets the pin to high

GPIO.cleanup()

GPIO.setup(17, GPIO.IN, GPIO.PUD_UP)

#11 on the BOARD GREEN Firewall

GPIO.setup(18, GPIO.IN, GPIO.PUD_UP)

#12 on the BOARD BROWN Lava

GPIO.setup(9, GPIO.IN, GPIO.PUD_UP)

#21 on the BOARD BLUE Mega Jump

GPIO.setup(4, GPIO.IN, GPIO.PUD_UP)

#7 on the BOARD ORANGE Puddle

GPIO.setwarnings(False) #switch off other ports

#Builds a wall of TNT which if the player hits will explode

def Firewall():

mc.postToChat(“Firewall Placed”)

TNT = 46,1

x, y, z = mc.player.getPos()

mc.setBlocks(x-6, y, z+2, x+6, y+10, z+3, TNT)

time.sleep(1)

#Lays Lava to slow down the other player

def Lay_Lava():

Lava = 10

check = 1

mc.postToChat(“Lava Deployed”)

while check == 1:

time.sleep(0.2 )

x, y, z = mc.player.getPos()

mc.setBlock(x-1, y, z, Lava)

check = 0

#Peforms a Mega Jump to lose players

def Mega_Jump():

time.sleep(0.1)

mc.postToChat(“Mega-Jump”)

x, y, z = mc.player.getPos()

mc.player.setPos(x, y+15, z)

time.sleep(1)

#Creates a Puddle to slow down your player

def Mega_Water_Puddle():

mc.postToChat(“Mega Water Puddle”)

time.sleep(0.2)

WATER = 9

x, y, z = mc.player.getPos()

mc.setBlocks(x-5, y, z-4, x-1, y, z+4, WATER)

time.sleep(1)

PiGlovePowerMoves.py

GPIO pins are a

physical interface

between the Pi and

the outside world.

At the simplest

level, you can

think of them as

switches that you

can turn on or off

(input) or that the

Pi can turn on or off

(output). The GPIO.

BCM option means

that you are referring

to the pins by the

“Broadcom SOC

channel” number.

GPIO.BOARD

speciﬁ es that you

are referring to the

pins by the number

of the pin and the

plug – the numbers

printed on the board.

GPIO pins

Tips | Tricks | Hacks

Most home

networks will use

IP addresses that

start with 192.168.1

and then a number

up to 255. An old

router will assign

these IP addresses

automatically. If

the router has Wi-Fi

then players can

also connect to

multiplayer using a

USB Wi-Fi dongle;

you are setting up

a LAN (Local Area

Network).

IP address

Below If you want to

get fancy, try using

the popper buttons

that Dan added to

his Pi Glove 2 project

07 Assign the power move to the button

Now you have a working button and a power move, you

can combine these two together. Basically, when you press the

button the power move will deploy. Once this is working you can

then set up the other three buttons with the same method. Open

a new Python window and type in the code below – save the ﬁ le

in the home folder. Start a

Minecraft

game as shown in Step 6

and then run the new program. Every time you press the button

you will place a TNT ﬁ rewall.

import time

from mcpi import minecraft

mc = minecraft.Minecraft.create()

import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BCM)

GPIO.setup(17, GPIO.IN, GPIO.PUD_UP)

#11 on the BOARD

def Firewall():

mc.postToChat(“Firewall Placed”)

TNT = 46,1

x, y, z = mc.player.getPos()

mc.setBlocks(x-6, y, z-2, x+6, y+10, z-1, TNT)

while True:

if GPIO.input(17) == 0:

Firewall()

10 Connect the wires

Now you are ready to connect the wires to the Raspberry

Pi to enable all four power moves to be used. Take one end of

each wire and connect them to the respective pins, as shown

below. The other end of the wire is placed into a ground pin. Note

that the RPi.GPIO pin numbering system is used here rather

than the physical pin number on the board – for example, GPIO

pin 17 is physical pin number 11. The following pins are used:

GPIO 17, pin 11 on the board

GPIO 18, pin 12 on the board

GPIO 9, pin 21 on the board

GPIO 4, pin 7 on the board

11 Set the network up

To interact with other players in the

Minecraft

world

you will need to set up a networked multiplayer game. This is

simple and can be achieved using an old router. Connect each

Raspberry Pi via an ethernet cable to the router and then back

to the ethernet port on each Raspberry Pi. Turn on the router and

wait about 30 seconds for the IP addresses to be assigned. Now

load up

Minecraft

and one of the players will start a new game.

12 Run the game!

After the game has loaded, the other connected player

will see an option to “connect to a multiplayer game”, usually

called Steve. The player selects this option and the networked

game will begin. You will be able to see two ‘Steves’ and the

Minecraft

chat will inform you that ‘Steve has joined the game’.

Open Python and the glove code, press F5 to run and you will be

able to see the power moves being deployed.

13 Interact in another player’s world

You’ll notice under the current setup that if the Pi Glove

is connected to the game and you use one of your power moves,

it will only appear in your

Minecraft

world and not in the other

players. This isn’t great, as the power move is supposed to stop

the other player! To resolve this, ﬁ nd the IP address of the other

06 Engage the ﬁ rewall

Start a new

Minecraft

game, then go to the Python

program and press F5 to run it. You may need to press the

Tab key to release the mouse from the

Minecraft

window. The

program will place a 12 x 10 wall of TNT behind the player every

ten seconds – you can blow them up but the Pi might lag.

09 Create the glove

Take your glove and attach the four

buttons to the fingers on the glove. There are a

number of ways to do this: glue the button

on, sew them in, stick them with double-

sided tape – the choice is up to

you. Wires can be hidden or on

display, depending on your

preferences and how you

want the glove to look.

08 Set up further buttons

Once you have one button working the next step is

to set up the other three using the same method from Step 2.

Take the button and connect the two wires to either side. At this

point you can add all three buttons and test them individually

for connectivity. Connect each set of button wires to the GPIO 17

and run the ﬁ rewall program. If the ﬁ rewall power move builds

on each click of the button, the connections and buttons are

working and you’re ready to attach the buttons to the glove.

Raspberry Pi Tips, Tricks & Hacks 149

Tips | Tricks | Hacks

14 Find your IP addresses

To find the IP address of a Raspberry Pi, load the LX

terminal, type ipconfig and press Enter – the address will

be displayed on the line that begins int addr:. This is the

number that you enter into the mc = minecraft.Minecraft.

create(“192.168.2.234”). Remember on the Glove Raspberry Pi to

enter the IP address of the other player’s Raspberry Pi, not yours.

15 Run both programs

No game would be complete without some healthy

competition and strategy. A second program is deployed by the

other player on the network which tracks and registers if they

catch or hit you. The program checks the block that they have hit

and compares it to the player’s location.

16 Test for hits

To check if the other player has hit you, run the second

program on the Raspberry Pi of the player who is doing the

chasing. The program basically ﬁ nds the other ‘glove’ players

current position and stores it in a variable. It then compares

the position that you hit with your sword, recording and storing

this too. The program then compares the values, if they match

then you have hit the other player and have won the game. If

not, get ready for a tirade of power moves. Note that in order to

monitor where the other player is, you must set the code line

mc1 = minecraft.Minecraft.create( ) to the IP address of the

Glove Raspberry Pi; for example, mc1 = minecraft.Minecraft.

create(“192.168.1.251”).

17 Game on

Now you are ready to play, check again that the IP

addresses are set for the other Raspberry Pi and not your

own. Build a new

Minecraft

world and start a new game on the

Raspberry Pi with the player who is chasing. When loaded, the

glove player joins the multiplayer game – this will be called Steve

(see Step 11). When loaded, you should see both players in the

world. Then run the ‘Pi Glove power moves’ program, and on the

other Pi run the ‘You hit me program’. Don’t forget to set the IP

addresses to each other Raspberry Pi.

Once set up, you can modify the power moves, use different

blocks and add new moves. You could create a timer and a

scoring system to track which player can survive the longest. If

you are feeling adventurous, you may want to make another

Power Glove, one for each player.

The program compares the values,

if they match then you have hit

the other player and have won the

game. If not, then get ready for a

tirade of power moves

#Main code to run

try:

lava_check = 0

mc.postToChat(“Minecraft Power Glove Enabled”)

while True:

if GPIO.input(17) == 0:

Firewall()

if GPIO.input(18) == 0: #needs to stop

Lay_Lava()

#GPIO.output(18, GPIO.LOW)

if GPIO.input(9) == 0:

Mega_Jump()

if GPIO.input(4) == 0:

Mega_Water_Puddle()

except:

print “Error”

import time

from mcpi import minecraft

mc1 = minecraft.Minecraft.create(“192.168.1.245”)

#The other players IP address goes here

mc = minecraft.Minecraft.create()

mc.postToChat(“###Here I come”)

Hit = 1

while Hit == 1:

#Find the block stood on

stood_x, stood_y, stood_z = mc1.player.getTilePos()

time.sleep(3)

blockHits = mc.events.pollBlockHits()

if blockHits:

for blockHit in blockHits:

if stood_z == blockHit.pos.z and stood_y == blockHit.pos.y+1:

mc.postToChat(“I got you”)

time.sleep(2)

mc.postToChat(“###GAME OVER###”)

time.sleep(1)

Hit = 0

mc.postToChat(“###Restart Hit Code”)

PiGlovePowerMoves.py (Cont.)

YouWereHit.py

Raspberry Pi, then enter this IP address into this line of code: mc

= minecraft.Minecraft.create( ). For example, mc=minecraft.

Minecraft.create(“192.168.2.234”), ﬁ lling the empty brackets

with the IP address of the other Raspberry Pi within your game.

Remember that this is the IP address of the other player’s

Raspberry Pi and not your IP address.

Full code

FileSilo.co.uk

The Raspberry Pi is actually quite powerful for

its price. On its own, though, you won’t be doing

any extraordinary calculations – or compiling

or anything strenuous at all, for that matter.

However, as it’s readily available and fairly cheap,

you can get twenty of them for the price of a new

computer. Each of them on their own will be no

different, but link them together over a network

and you can have them share their power and vastly

increase the amount they can process.

This kind of setup is generally known as a

Beowulf cluster, so named for the eponymous hero

of the epic poem in which Beowulf is described

as having “thirty men’s heft of grasp in the gripe

of his hand”. It’s not ridiculously hard to achieve,

either – all you need is a lot of Raspberry Pis, a bit

of Python know-how and a reason to use it. This

makes it a good project for things like classrooms,

after-school Pi clubs and the like – really, anywhere

there’s a collection of Pis available for general use.

The more Raspberry Pi nodes you add into the

setup, the more powerful it will become, which

means you can start with just two or three at home

and then gradually add more and more to your

cluster, if you want to. And because of the way it all

works, you can hook in and control your SuperPi

cluster from your main computer as well, making

this as accessible at it is scalable.

Over the next few pages we’ll show you how to

get your Pis set up ready for use, including all the

tools you’ll need, how to get them all connected and

then ﬁ nally what you can do with all that processing

power. We’d love to see your SuperPi once it’s

ﬁ nished – drop us a tweet (@Books_Imagine)!

Pool the resources of multiple

Pis to create your own scalable

Pi supercomputer

150 Raspberry Pi Tips, Tricks & Hacks

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 151

Tips | Tricks | Hacks

152 Raspberry Pi Tips, Tricks & Hacks

Get your Pis set up to talk to one other

and share their processing power

Programming your Pis

01Fully updated Pi

It’s very important that your Raspberry Pi computers

are fully updated for this, so make sure everything is

compatible, including the ﬁ rmware. This can be done

with three commands in succession, and make sure you do it

on every Pi in turn:

$ sudo apt-get update

$ sudo apt-get upgrade

$ sudo rpi-update

02Get the MPI module

Install the mpi4py Python module in the terminal by

using the following command (again, on every Pi):

$ sudo apt-get install python-mpi4py

The module will also work on Arch or other Raspberry Pi distros,

although you’ll need to add it manually or install it via pip.

03 Create your threads

To use MPI in Python, ﬁ rst import it with:

from mpi4py import MPI

The most important part of the code is telling MPI how to

rank the threads and recognise their size. Do this with:

comm = MPI.COMM_WORLD

rank = comm.Get_rank()

size = comm.Get_size()

What you’ll need

Q As many Raspberry Pi

computers as you want

Q SD card with up-to-date

version of Raspbian

Q mpi4py MPI python module

pypi.python.org/pypi/mpi4py

Q Updated ﬁ rmware on

Raspberry Pi

Left If you want the SuperPi to

become a reality then updating

everything is crucial

The mpi4py library

can also be used

with Numpy, the

numerical and

mathematics

module for Python.

This can be installed

using sudo apt-get

install python-

numpy, and is very

useful for doing

the kind of large

calculations that

a cluster would

be making. We’ll

be using it in our

example over on

the next page, so

install it now.

Other

libraries

Raspberry Pi Tips, Tricks & Hacks 153

04 Send and receive data

Sending data is quite easy: you need to give it a

destination thread so MPI knows what it is when it returns,

halting the original thread until it does:

data = [1.0, 2.0, 3.0, 4.0]

comm.send(data, dest=1, tag=0)

data = comm.recv(source=0, tag=0)

The tags allow you to parse what to do with some speciﬁ c

types of data.

05 Run the code

So that’s the basics of how your code can be

sent throughout a cluster. To actually activate the code

and choose the Raspberry Pi recipients, you will need to write

this in a terminal:

$ mpirun -host 192.168.1.20,192.168.1.21,192.168.1.22

python superpi.py

…with the IP addresses being the ones that are on the

other Raspberry Pis.

06 Will it work?

What we’ve done above won’t really do anything, but it

at least illustrates how you can send code around the network.

You can do it for any type of calculating but, due to some of the

network lag, it’s only worth it for large numbers and bigger data.

from __future__ import division

import numpy as np

from mpi4py import MPI

# Grab parutils from FileSilo.co.uk and put it in the same folder

as this. Use it to then print the number of cores used

from parutils import pprint

comm = MPI.COMM_WORLD

pprint("-"*78)

pprint(" Running on %d cores" % comm.size)

pprint("-"*78)

# Set up a ranking structure for the different nodes

my_N = 4

N = my_N * comm.size

if comm.rank == 0:

A = np.arange(N, dtype=np.float64)

else:

A = np.empty(N, dtype=np.float64)

my_A = np.empty(my_N, dtype=np.float64)

# Scatter data into my_A arrays

comm.Scatter( [A, MPI.DOUBLE], [my_A, MPI.DOUBLE] )

pprint("After Scatter:")

for r in xrange(comm.size):

if comm.rank == r:

print "[%d] %s" % (comm.rank, my_A)

comm.Barrier()

# Everybody is multiplying by 2

my_A *= 2

# Allgather data into A again and print results

comm.Allgather( [my_A, MPI.DOUBLE], [A, MPI.DOUBLE] )

pprint("After Allgather:")

for r in xrange(comm.size):

if comm.rank == r:

print "[%d] %s" % (comm.rank, A)

comm.Barrier()

Full code listing

Mpi4py will also

work on Arch or other

Raspberry Pi distros

Right You’ll need to know the IP

addresses of each Raspberry Pi, so

be sure to note those all down now

Tips | Tricks | Hacks

154 Raspberry Pi Tips, Tricks & Hacks

Now you’ve programmed your Raspberry Pi

units, it’s time to link them together

Construct your SuperPi

Programming the Raspberry Pis is one part of constructing

your supercomputer – properly housing them together

is another problem. The very basic things you require to

get them to work is power and a local network via a router

and/or switches. This then extends to cases, SD cards and even

Raspberry Pis themselves.

To make sure you get the most out of the system,

you’ll have to get the right selection of components to power

and connect them.

Power supply

A good power supply is extremely important when

powering a Raspberry Pi, otherwise it will power on and

run but you won’t be able to get the most out of it. If you’re

using the Model B+ and notice a rainbow square in the

corner, that’s an indication you’re not giving it enough power.

You won’t need the maximum amount of power in your

cluster, as you won’t be powering a display or a camera or

possibly anything off the GPIO ports, so the recommended

two amps may be a little overpowered for your needs, even if

you do push the processor to its limits. However, if you plan

to do any overclocking then the two-amp power supply will

become more and more necessary, and it’s a lot better to be

on the safe side.

As your cluster grows you’ll also need to make sure you

have plenty of surge protection as the Raspberry Pis can be

extremely sensitive.

We recommend:

Raspberry Pi Universal Power Supply

pimoroni.com

Networking

The more Raspberry Pis you plan to connect up, the more

networking you will need to hook them together. The best

method to do this is via cable, as it will carry any messages

faster and with less latency than wireless – but creating

the cluster isn’t as easy as plugging it into a router, though.

With more Pis you’ll need more ports, and this can be

accomplished by getting network switches. These are dumb

connectors that contain no routing or address system, but

allow you to connect more devices up to a central router.

Even though we recommend cabling, you can still use

wireless to connect extra Pis. This also has the effect

of cutting down on the amount of cabling and network

switches you can use, but in general it’s better to have a

homogenous setup.

You won’t need the maximum

amount of power in a cluster, as

you won’t be powering a display

or a camera off the GPIO ports

If you ﬁ nd you

still want a little

extra power from

your cluster, you

could always try

overclocking your

Raspberry Pis.

In Raspbian, you

can do this from

the conﬁ g menu,

accessible via sudo

raspi-conﬁ g. In the

menu you will ﬁ nd an

option to overclock

with a few levels to

select from. You can

do this on separate

Raspberry Pis or

all of them, but be

aware that doing

so can shorten the

lifespan of a Pi CPU,

especially when set

to the highest level.

Overclock

Tips | Tricks | Hacks

Raspberry Pi Tips, Tricks & Hacks 155

Cases

There are many types of cases for a lot of Raspberry Pi uses: from simplistic

plastic cases to protect the Pi from dust, to fully water- and weather-proof metal

shells. One of the most versatile cases is the Pimoroni Pibow, which comes in a

variety of sizes and conﬁ gurations for all versions of the Raspberry Pi. The cases are

all held together by screws that can easily be repurposed to help mount the Pis in

a tower or other conﬁ guration so that they don’t take up as much horizontal space.

They can be a little slower to get your Raspberry Pi into than some cases, but

they’re quite durable and easily customisable if you want to move them, or add a

small touchscreen or scrolling LCD screen to the main Raspberry Pi to keep an eye

on things without needing to SSH in.

We recommend:

Pimoroni PiBow

pimoroni.com

SD cards

SD card selection is a minor but still important factor when creating your cluster.

Some Raspberry Pis come with an SD card which should be suitable enough, but

others you’ll need to buy some cards for. We recommend getting 4GB cards; while

a 2GB card will do the job, 4GB allows you to use NOOBS if you have to and is also

future-proof for larger distros and operating systems. As the Model B+ requires a

micro SD card, make sure you have the right ratio of SD and micro SD cards.

When it comes to getting the SD cards all set up and homogenous, the easiest

and quickest method is to ﬁ rst do all the installing and updating on one Raspberry

Pi, minus the ﬁ rmware update with rpi-update. Then create a copy of the disk by

putting it into a Linux system, open up the terminal and use:

sudo dd bs=1M if=/dev/[SD card location] of=superpi.img

Once it’s copied, you can write this to all the other cards using:

sudo dd bs=1M if=superpi.img of=/dev/[SD card location]

We recommend:

4GB

pimoroni.com

Raspberry Pis

It actually doesn’t really matter what type of Raspberry Pi you use in your

cluster – you could use a homogenous selection of the latest Model B+ or even have

a mixture of the B+, B and Model As connected to each other. As long as you have

them running the same software and possessing the relevant scripts, the system will

work. The main differences you might encounter are the differing power draws between

devices and that the Model As might be slightly slower for some calculations.

The Model A types do have a disadvantage in that they do not have an ethernet

port built-in. However, they can still make use of a wireless dongle to connect to the

overall network of Raspberry Pis.

Make sure you set a static IP address for each Raspberry Pi with a speciﬁ c range

covering their location on the network. This is helpful for two main reasons, the ﬁ rst

one being the ability to always be able to call the correct address when running MPI,

and the second being that you can then SSH in and maintain your Pis from afar.

We recommend:

Model B+

element14.com

Tips | Tricks | Hacks

156 Raspberry Pi Tips, Tricks & Hacks

Your supercomputer is ready to crunch

some code. What will you have it do?

How to use your

Super Raspberry Pi

Donate power with BOINC

BOINC is the computer network system that allows you to donate

idle CPU power to crunch big data, such as folding proteins or

analysing signals from the cosmos to look for alien life. There’s

a speciﬁ c app add-on for BOINC that lets you spread the workload

across the MPI network and treat them all as extra CPU threads rather

than extra units. The app details can be found here: bit.ly/1BBTS0W.

The Ras Pi on its own won’t be able to add much to the pool, but

linking several together can really boost the performance and create a

powerful little node to help out with some projects. There are several

you can donate processing power to involving science, medicine and

maths. You can tweak BOINC to use more than just idling Pi power.

Quick compiling

Now you have a lot more processing power at your disposal,

you can try compiling Raspberry Pi programs on the cluster

rather than just on the single Raspberry Pi. These will only

really work on another Raspberry Pi, though, and compiling

on a single Raspberry Pi can be extremely time-consuming

compared to compiling on a proper PC or laptop.

There is, however, also a selection of MPI-only applications

that can be built using your cluster to increase the

functionality of cluster without relying on Python code. These

must include speciﬁ c MPI commands in the source code

to make sure they run properly, which can be done a little

differently than in our Python example. Look up the best

practices for your programming language and if there are any

extra modules or plugins you’ll need for it. You can test the

code in a similar way to how we tested the Python code.

Modelling and simulations

Python and other languages can be used to create models of complex

systems. Such models can include planetary orbits and objects

interacting with them, huge mathematical equations and any resulting

graphs for tides, the weather and much more. Many of these use a lot of

calculations and can be slow even on a normal PC. Give them a lot more

cores and you can get much faster, and sometimes more accurate, results.

Mathematica also contains some level of cluster support that works

via Open MPI, the software we’re using to link the Raspberry Pi network

together. Wolfram has information on how it works and how to use it on

their website (bit.ly/1oEYVb8), and it can really help with crunching the

amount of data you can access and use in Mathematica.

Tips | Tricks | Hacks

Find out more about MPI, Python and other

ways to make use of your Super Pi

Resources

You can learn how to do

much more than just

multiply numbers

Open MPI

open-mpi.org

Open MPI (right) is the implementation of MPI that our

Python module uses to send and receive data over the

Raspberry Pi network. It supports all three major versions of

MPI and, importantly, provides it in an open source format for

everyone to use. There’s full documentation for the extended

library on the forums (www.mpi-forum.org) if you need to

extend it past Python programs and take a little more control

of what you’re calculating and how.

mpi4py documentation

pythonhosted.org//mpi4py/usrman/index.html

The Python module we’re using has many more functions

than the one we’re using, and they’re all contained in the

documentation available on their website. You can learn

how to do much more than just multiply numbers, as we

showed you in our example, including the use of wrappers for

other code, matrices of data and a couple other functions. It’s

very ﬂ exible and still in development so it’s worth checking

in on it and the change logs every now and then for new or

different functions.

Raspberry Pi forums

raspberrypi.org/forums

For anything going wrong with your Pi beyond

MPI, your ﬁ rst port of call should always be

the Raspberry Pi forums. The users are well

experienced in using the Raspberry Pi and

Linux, and will usually be able to help out. If you can

give precise details and log ﬁ les along with your post, they

might be able to help you quicker.

Raspberry Pi Tips, Tricks & Hacks 157

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Get inventive

Take your Pi to the next level by

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Create with Pi

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Master the basics

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Practical projects Essential upgrades  Python tips

Raspberry Pi Tips, Tricks & Hacks Volume 1 Second Revised Edition Tips

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