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

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NEW Practical projects Essential upgrades Python tips 10FREE DISTROS Raspberry Pi Pi Zero 40 PI NS :2 8x GP IO ,I 2C ,S PI ,U AR T tricks inside Over SD CA RD 40 Raspberry Pi projects Welcome to Raspberry Pi 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 touchscreen 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! Raspberry Pi Imagine Publishing Ltd Richmond House 33 Richmond Hill Bournemouth Dorset BH2 6EZ +44 (0) 1202 586200 Website: www.imagine-publishing.co.uk Twitter: @Books_Imagine Facebook: www.facebook.com/ImagineBookazines Publishing Director Aaron Asadi Head of Design Ross Andrews Production Editor Alex Hoskins Senior Art Editor Greg Whitaker Designer Perry Wardell-Wicks Photographer James Sheppard Printed by William Gibbons, 26 Planetary Road, Willenhall, West Midlands, WV13 3XT Distributed in the UK, Eire & the Rest of the World by Marketforce, 5 Churchill Place, Canary Wharf, London, E14 5HU Tel 0203 787 9060 www.marketforce.co.uk Distributed in Australia by Network Services (a division of Bauer Media Group), Level 21 Civic Tower, 66-68 Goulburn Street, Sydney, New South Wales 2000, Australia, Tel +61 2 8667 5288 Disclaimer The publisher cannot accept responsibility for any unsolicited material lost or damaged in the post. All text and layout is the copyright of Imagine Publishing Ltd. Nothing in this bookazine may be reproduced in whole or part without the written permission of the publisher. All copyrights are recognised and used specifically for the purpose of criticism and review. Although the bookazine has endeavoured to ensure all information is correct at time of print, prices and availability may change. This bookazine is fully independent and not affiliated in any way with the companies mentioned herein. Raspberry Pi is a trademark of The Raspberry Pi Foundation Raspberry Pi Tips, Tricks & Hacks Volume 1 Second Revised Edition © 2015 Imagine Publishing Ltd Part of the bookazine series Contents Tips 32 28 5 Practical Raspberry Pi Projects 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 52 40 50 ways to master Raspberry Pi 48 Use an Android device as a Pi screen 12 Set up your Raspberry 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 • 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 with Python 68 Install Android on Pi Make a tweeting bird watcher 76 Add a battery pack to Pi “Use a motion-sensing Raspberry Pi to automatically take pictures” 6 Raspberry Pi Tips, Tricks & Hacks 68 “It has powered quadcopters, coffee makers, self-sailing boats and even touched the edge of space” 80 Tricks 80 10 Inspiring Pi Projects • Retro arcade cabinet • Audiobook reader • Web radio Hacks • Media caster 132 Build a Raspberry • 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 Pi-controlled car 138 Make a Raspberry Pi 106 car computer 146 Build a Minecraft power move glove 150 Build a Super Raspberry Pi 120 Master Raspberry Pi in 7 days Master Raspberry Pi in 7 days From setup to internet sensation in a week… 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 ﬁnd over the next 16 pages will certainly get you off on the right 8 Raspberry Pi Tips, Tricks & Hacks foot. Our ﬁnal 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, ﬁrst 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 ﬁnal project – and much more besides… Master Raspberry Pi in 7 days Raspberry Pi Tips, Tricks & Hacks 9 Master Raspberry Pi in 7 days Plan your week Day 1 Set up your Raspberry Pi Day 2 Make a game from Scratch It’s not rocket science, but we’ll get you started Learn the basics of coding with graphical feedback Day 3 Learn code with Sonic Pi Day 4 Take photos with your Pi Write functional code while making beautiful music Use Python to take great snaps with your camera Day 5 Get to grips with GPIO Create a simple but elegant candlelight project Day 6 Use the Twitter API Create an Internet of Things Twitter lamp 10 Raspberry Pi Tips, Tricks & Hacks Day 7 Put it all together! Automagically share wildlife shots with this motionsensing, picture-taking, Twitter-posting project 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 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 modiﬁed 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 Raspberry Pi camera board The Pi-speciﬁc 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 Electronics starter kit 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 PIR sensor 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 Raspberry Pi Tips, Tricks & Hacks 11 Tips | Tricks | Hacks Pi in 7 days Master Raspberry 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 Set up your Raspberry Pi Turn your Raspberry Pi into a fully functional PC and get to know the basics of setting it up 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. 12 Raspberry Pi Tips, Tricks & Hacks 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 ﬁle; download it onto the SD card for your Raspberry Pi and extract the ﬁles from it here. Do not extract the ﬁles elsewhere and copy them over. Master Raspberry Pi in 7 days 07 Get new software 08 Get an ofﬁce suite 09 Get a better browser 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 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 conﬁg 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. 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 03 Choose your distro Plug in your SD card and ﬁnally 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. 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. Conﬁrm that you want to install, and it will go through the process of adding Raspbian to the SD card. Raspbian does not have any form of ofﬁce functionality by default, only a basic text editor. You can add LibreOfﬁce though, which can be done via the Pi Store. Open up the Store and go to Apps; here you’ll ﬁnd LibreOfﬁce as a free download. Once you’ve created an account, it will download and install it. Once that’s ﬁnished, follow it up with: $ sudo apt-get upgrade This may end up taking a few minutes, but it will update the software throughout Raspbian. 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 The other distros each have their uses and you may want to use them at a later date Raspberry Pi Tips, Tricks & Hacks 13 Master Raspberry Pi in 7 days 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. 14 Raspberry Pi Tips, Tricks & Hacks 01 The ﬁrst 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 Building blocks Preview Test your code straight away to make sure it does what you expect it to do Use blocks that represent coding to build your game or animation Code logic Build project Slot the blocks together in a straightforward manner to create loops and comparisons 02 Export to the Scratch website to show off your work to the world 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 ﬁeld. 03 Simple bouncing 08 Random bouncing 09 Further developments Pressing the green ﬂag 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. 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. 04 07 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 ﬂag it resets to the ball. 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. Go the Operators menu and select the ﬁrst value, blank + blank. Drag it to where we have 180 degrees in the turn block, and add 180 to the ﬁrst 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. 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. Raspberry Pi Tips, Tricks & Hacks 15 Master Raspberry Pi in 7 days 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 16 Raspberry Pi Tips, Tricks & Hacks 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 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. Sonic Pi offers you a very simple language style that can ease you into the basics of working with code Full code listing with_tempo 200 play_pattern [40,25,45,25,25,50,50] 03 Your ﬁrst note Our ﬁrst 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. 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.times do if rand < 0.5 play 30 else play 50 end sleep 2 end end 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. 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 ﬁnite loop with the x.times function. ‘Do’ and ‘end’ signify the start and end of the loop. 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 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. Raspberry Pi Tips, Tricks & Hacks 17 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 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 beneﬁts 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 speciﬁc 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 What you’ll need Q Raspberry Pi camera board Q picamera github.com/waveform80/picamera Master Raspberry Pi in 7 days Carefully insert the connector for the camera board, making sure it’s the right way round 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() 07 Test explained 08 Python video 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. 02 Enable the camera First you’ll need to make sure the camera modules are enabled. To start the standard conﬁguration screen, open a terminal and type: $ sudo raspi-config Navigate down to Enable Camera, press Enter, and then simply key over to enable and conﬁrm with another press of Enter. Select Finish and then reboot. 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 ﬁve seconds that make up the preview as well. To record video with picamera, you need to ﬁrst set the resolution and then set a recording time. 03 Take your ﬁrst 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 ﬁve-second preview of the input of the camera and then capture the last frame of the video. 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 ﬁrst though, and you can do so from the terminal, using the following command: $ sudo apt-get install pythonpicamera import picamera camera = picamera.PiCamera() camera.resolution = (640, 480) camera.start_recording(‘firstvideo.h264’) camera.wait_recording(60) camera.stop_recording() camera.close() 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. Raspberry Pi Tips, Tricks & Hacks 19 Master Raspberry Pi in 7 days 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 ﬁnal 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). 20 Raspberry Pi Tips, Tricks & Hacks 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 ﬁrst 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 ﬁrst 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 Conﬁgure the GPIO module 04 Basic functions 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. 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 ﬁrst 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 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 5v 2 5v 3 Ground 4 14 Ground 15 #!/usr/bin/env python 17 18 # Import the modules used in the script import random, time import RPi.GPIO as GPIO 27 Ground 22 23 3.3v 24 10 Ground 9 25 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 11 8 Ground 7 loop through the program. random.random picks a ﬂoating point number between 0 and 1 – we divide this by WIND to help achieve our ﬂicker 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 ﬂicker function. When we want to quit this otherwise inﬁnite 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 The General Purpose Input/ Output pins give you the power to interact with the real world using your Raspberry Pi 3.3v 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 ﬂickering as if it’s a candle in a light breeze. Take some time to experiment with the variables in the brightness and ﬂicker functions to achieve a more desirable effect. Full code listing # 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 = True 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() Raspberry Pi Tips, Tricks & Hacks 21 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… 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 ﬂashes 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. What you’ll need Q tweepy Q Internet connection Q Breadboard Q Male-to-female cables Q 300ohm resistor Q LED 22 Raspberry Pi Tips, Tricks & Hacks Master Raspberry Pi in 7 days 04 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! 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 ﬂash 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. It’s amazing what you can achieve in just 50 lines of Python 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 ﬂash. 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 ﬂash 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 ﬁlter 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 Full code listing #!/usr/bin/env python class StreamListener(tweepy.StreamListener): #import the required libraries import tweepy import time import RPi.GPIO as GPIO # 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) # 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() def on_error(self, error_code): print "Error:", error_code return False # These are the words we're looking out for on Twitter terms = ['raspberry pi', 'raspberrypi', 'raspi'] # Configure the GPIO port as we did in the last project led = 18 # Configure the stream and filter only our chosen terms try: listener = StreamListener() stream = tweepy.Stream(auth, listener) stream.filter(track = terms) GPIO.setmode(GPIO.BCM) GPIO.setup(led, GPIO.OUT) except KeyboardInterrupt: print "\nQuitting" # Set the led light to be 'on' GPIO.output(led, GPIO.HIGH) # Don't forget to clean up after so we # can use the GPIO next time finally: GPIO.cleanup() print my.name, "is connected! Press CTRL + C to quit." # We've tweaked the class that monitors Twitter's stream Raspberry Pi Tips, Tricks & Hacks 23 Master Raspberry Pi in 7 days What you’ll need Q tweepy Q Internet connection Q HC-SR501 PIR Infrared sensor Q Camera board & picamera library The tweeting bird watcher Our ﬁnal project! Create an Internet of Things device able to takes pictures of wildlife before tweeting them to the web We’ve reached the end of the week and we’re now ready to take on our biggest project yet. Our ﬁnal 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. 24 Raspberry Pi Tips, Tricks & Hacks 01 Conﬁgure 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 easyto-conﬁgure 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 conﬁgured 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 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 ﬁrst, using simple print statements to show when motion has been detected. Visit github.com/russb78/tweety-pi and explore the project to ﬁnd the pir_testing.py script. Copy it onto your Pi and run it with your PIR connected. You’ll probably ﬁnd that it’s over-sensitive for your needs by default. You’ll ﬁnd 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. 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. 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. 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. 06 Main program loop As we’ve done before, we’re placing our main program loop in try, except, ﬁnally 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 inﬁnite loop to ensure the script keeps running. Pressing Ctrl+C will break this loop, causing the program to end, but not before ﬁnally calling the methods that close the camera and shutoff 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! Full code listing #!/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', 'image_' + str(pics_taken) + '.jpg')) pics_taken += 1 print "Picture taken! Tweeting it...""" update_twitter() def update_twitter(): api.update_with_media(os.path.join( 'pics', 'image_' + str(pics_taken -1) + '.jpg'), 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() Raspberry Pi Tips, Tricks & Hacks 25 Tips 28 5 Practical Raspberry Pi Projects • Make music with the Raspberry Pi • Raspberry Pi voice synthesiser • Program Minecraft-Pi • Get interactive with Scratch • Build a Raspberry Pi web server 30 40 Why You Need Python 3 48 Use an Android device as a Raspberry Pi screen 52 Host a website on your Raspberry Pi 32 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 66 Remotely control Pi 68 Install Android 76 Add a battery pack to Raspberry Pi 26 Raspberry Pi Tips, Tricks & Hacks 38 “This isn’t a random selection. These are practical ideas designed to help kick-start bigger and better things” 48 64 76 Raspberry Pi Tips, Tricks & Hacks 27 Tips | Tricks | Hacks 28 Raspberry Pi Tips, Tricks & Hacks Tips | Tricks | Hacks 5 PRACTICAL RASPBERRY PI PROJECTS Still haven’t done anything with your Raspberry Pi? Follow along with our expert advice and kick-start your own amazing 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 beneﬁtting from doing things the open source way… Raspberry Pi Tips, Tricks & Hacks 29 Tips | Tricks | Hacks Make music with the Raspberry Pi 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 QSonic Pi is a great way to learn basic coding principles and have fun 30 Raspberry Pi Tips, Tricks & Hacks 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 Tips | Tricks | Hacks “We can start making more complex melodies by using more of Sonic Pi’s functions” 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. 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. 03 Your ﬁrst note Our ﬁrst 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. You’ll learn... Full code listing 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 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 ﬁnite 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. play_pad “saws”, 3 in_thread do with_synth “fm” 6.times do if rand < 0.5 play 30 else play 50 end sleep 2 end 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 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 contextsensitive chips, chirps and beeps and use it to give a familiar voice while it tootles around. 06 3 MIDI 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. The Musical Instrument Digital Interface is a standard for digital music, and the numbers and tones used in Sonic Pi make use of this. Raspberry Pi Tips, Tricks & Hacks 31 Tips | Tricks | Hacks Q It’s easier to make your Raspberry Pi talk than you might think, thanks to eSpeak Raspberry Pi voice synthesiser Add the power of speech to your Raspberry Pi projects with the versatile eSpeak Python library What you’ll need Q Portable USB speakers Q python-espeak module QeSpeak QRaspbian (latest image) 32 Raspberry Pi Tips, Tricks & Hacks 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 ofﬁce. 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 Tips | Tricks | Hacks “You can change the way eSpeak will read text with a number of different options” 02 Pi’s ﬁrst words The eSpeak library is pretty simple to use – to get it to just say something, type in the terminal: $ espeak “[message]” 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! This will use the library’s defaults to read whatever is written in the message, with decent clarity. Full code listing 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. Import the necessary eSspeak and GUI modules, as well as the module to ﬁnd out the time Deﬁne the different functions that the interface will use, including a simple ﬁxed 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 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. 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. The text entry appends to the variable we created, and each button calls a speciﬁc function that we deﬁned above in the code Get the code: from espeak import espeak from Tkinter import * from datetime import datetime bit.ly/ 14XbLOC 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”).pack() 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() Raspberry Pi Tips, Tricks & Hacks 33 Tips | Tricks | Hacks Program Minecraft-Pi Learn to program while playing one of the greatest games ever made! 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 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 ﬁrst glance Minecraft-Pi is a simpliﬁed version of the Pocket Edition (designed for tablets and smartphones), the Raspberry Pi edition is very special, in that it’s the only version of 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 conﬁgure 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. Tips | Tricks | Hacks 02 Installation Make sure you’re already in your home folder and download the MinecraftPi 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 ﬁrst 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 ﬂy. 04 Conﬁguring 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 Full code listing # !/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)) You’ll learn... 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. 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! 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 ﬁnd on www.stuffaboutcode.com). When you launch the script, you’ll be challenged to ﬁnd 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. Raspberry Pi Tips, Tricks & Hacks 35 Tips | Tricks | Hacks Q Scratch can be used to do Internet Of Things projects with a few tweaks Get interactive with Scratch Experiment with physical computing by using Scratch to interact with buttons and lights on your Pi What you’ll need Q Breadboard Q LEDs Q Buttons Q Resistors Q Jumper wires Q ScratchGPIO3 36 Raspberry Pi Tips, Tricks & Hacks 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). Tips | Tricks | Hacks 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. You’ll learn... 1 Simple circuits 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 ﬂow 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 echo echo echo 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 17 > /sys/class/gpio/export out > /sys/class/gpio/gpio17/direction 1 > /sys/class/gpio/gpio17/value 0 > /sys/class/gpio/gpio17/value 05 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 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: 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 ﬁrst project might just turn a light on and off, but with that skill banked, the sky is the limit. echo 4 > /sys/class/gpio/export echo in > /sys/class/gpio/gpio4/direction watch -n 0.5 cat /sys/class/gpio/gpio4/value 06 04 2 Coding principles Let there be light! Boot up the Pi and start ScratchGPIO3 as before. Go to the control section and add when green ﬂag 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 ﬂag. If you push the button, the LED will light up! Raspberry Pi Tips, Tricks & Hacks 37 Tips | Tricks | Hacks Q Google Coder is a brilliant way to introduce yourself to web development Build a Raspberry Pi web server Use Google Coder to turn your Raspberry Pi into a tiny, low-powered web server and web host What you’ll need Q Internet connectivity Q Web browser Q Google Coder googlecreativelab.github.io/coder/ raspberrypi/sonicpi/teaching.html 38 Raspberry Pi Tips, Tricks & Hacks We’re teaching you how to code in many different ways on the Raspberry Pi this issue, so it only seems ﬁtting 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 speciﬁcally 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 Tips | Tricks | Hacks Full code listing HTML 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: Some simple HTML code that can point us to some important websites. The h2 tag is used to display the time thanks to Java

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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 ﬁrst 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 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”).html(time);

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

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