Powermon Guide Rev1 0

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Powermon Guide

Rev. 1.0

03/10/2019

Table of Contents
1 Description............................................................................................................................................1
2 Usage.....................................................................................................................................................2
2.1 Scenarios.......................................................................................................................................2
2.2 Run Menu......................................................................................................................................3
2.2.1 Fields:....................................................................................................................................4
2.2.2 Status:....................................................................................................................................5
2.2.3 SNAPSHOT:..........................................................................................................................5
2.2.4 CLEAR:.................................................................................................................................5
2.2.5 START:..................................................................................................................................5
2.3 Other Menus..................................................................................................................................6
2.3.1 Setup:.....................................................................................................................................7
2.3.2 Limits:....................................................................................................................................8
2.3.3 Calibration:............................................................................................................................9
3 Source and data files.............................................................................................................................9
4 Installation...........................................................................................................................................10

Description

Powermon is a device built around the Texas Instruments INA219 chip, that can simultaneously
measure DC voltage and current and therefore calculate power. Powermon also measures run time and
which allows it to calculate capacity (mAh) and energy (mWh) for testing batteries. The accuracy of
voltage and current measurements is 0.5%. The current accuracy depends of course on the tolerance of
the shunt resistor. It uses an internal 0.1 Ohm 1% shunt but external shunts can be connected to extend
the current range. Powermon allows voltage and current measurements to be calibrated to get better
than 0.5% if a suitable reference is available and stores the calibration values for different shunts.
The voltage range is limited to 0..26V DC maximum (without protection diodes). With protection
diodes shown in the schematic, the voltage is limited to 0..20V. The voltage must never get negative
or exceed the maximum voltage or you will damage the INA219 chip.

Specs:
Table 1: Basic specs
Voltage
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0..20VDC in 10 mV resolution
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Voltage is internally measured and

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recorded in 4mV resolution but displayed
in 10 mV resolution
Current

0..±400mA in 12.5uA resolution
0..±800mA in 25uA resolution
0..±1.6A in 50uA resolution
0..±3.2A in 100uA resolution

(0.1 Ohm shunt)
Burden voltage: 100 mV/A

Powermon calculates the following parameters which can be selected for displayed
Table 2: Parameters that are measured (or calculated) and displayed or recorded
Measurement

Display

Snapshot recording

Recording

Voltage (bus or load,
selectable)

Always: upper left

Yes

Current

Always: upper right

Yes

Power

Selectable field

Yes

Capacity

Selectable field

Yes

Energy

Selectable field

Yes

Run time

Selectable field

Yes

Highest voltage

Selectable field

Yes

Average voltage

Selectable field

Yes

Lowest voltage

Selectable field

Yes

Highest current

Selectable field

Yes

Average current

Selectable field

Yes

Lowest current

Selectable field

Yes

Highest power

Selectable field

Yes

Average power

Selectable field

Yes

Lowest power

Selectable field

Yes

INA219 shunt voltage

Selectable field

Yes

INA219 bus voltage

Yes

INA219 power

Yes

Sample count

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Yes

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Usage
2.1

Scenarios

Powermon

Charger

battery

Figure 1: Measuring charge into a battery
Powermon

battery

Figure 2: Measuring battery capacity
shunt

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battery

Figure 3: Using an external shunt

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Figure 1 shows the basic wiring to measure the
charge flowing into a battery. The charge begins
when the relay is (manually) activated. The
LIMITS function allows the charge to be
terminated when one of the thresholds is
exceeded, for example run time.
To measure the voltage of the battery (and not the
charger), SETUP-VOLTS must be set to V =
LOAD
Figure 2 shows the basic setup to measure the
capacity of a battery by discharging it into a load.
The discharge begins when the relay is activated
and can be automatically terminated when one of
the LIMITS thresholds is reached, for example a
minimum voltage. To measure the voltage of the
battery (and not the load), SETUP-VOLTS must
be set to V = SUPP.
Figure 3 shows how to connect an external shunt
resistor to extend the current range. The wire
bridge between the two red terminals must be
removed for this. The value of the external shunt
must be selected in the SETUP-SHUNT menu and
Powermon should have been calibrated before,
using this external shunt.
Note that the max. current for the relay is 10A.
For higher currents, the internal relay must be
bypassed by connecting the load to the yellow
terminal instead.

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Run Menu

The standard display while doing measurements is the Run Menu. It also comes up automatically after
power-up. While in the run menu, the display looks like Figure 4 below
Auto or Manual range
and range values

Voltage

Current

shunt volt range:
Auto Man
40 mV:
A
a
80 mV:
B
b
160mV:
C
c
320mV:
D
d

LEFT
FIELD

RIGHT
FIELD

Figure 4: Run Menu display
The button assignments in the run menu are shown in Table 3
Table 3: Button assignments in the Run Menu
PREV

SEL

Short
press

cycle through field options SNAPSHOT
for the LEFT field

Long
press

In manual range:
decrements range

2.2.1

BACK

cycle through field options Return to main menu
for the RIGHT field

Toggles between auto and In manual range:
manual range mode
increments range
in auto range: CLEAR

START

Fields:

Using short presses on the PREV or the NEXT buttons cycles the left or right fields through one of 16
options for display. These are:
(1)

empty (nothing is shown)

(2)

capacity (mAh)

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(3)

energy (mWh)

(4)

power (W)

(5)

Run time (hh:mm:ss)

(6)

Highest voltage (V)

(7)

Average voltage (V)

(8)

Lowest voltage (V)

(9)

Highest current (A)

(10)

Average current (A)

(11)

Lowest current (A)

(12)

Highest power (W)

(13)

Average power (W)

(14)

Lowest power (W)

(15)

Shunt voltage (mV)

(16)

Status

2.2.2

Status:

An example of the status display selected in the left field is shown below:

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R : Recording ON
- : Recording OFF

High (max) Energy limit
High (max) Capacity limit

L : Volt = load side
S : Volt = supply side

High (max) Time limit
High / Low Current limits

:
:
:
:

03/10/2019

no limit set
hi limit set
lo limit set
hi+lo limits set

Blink = limit reached

High / Low Voltage limits

Figure 5: Run Menu display with status

2.2.3

SNAPSHOT:

When pressed, Powermon takes a snapshot of most of the parameters that are currently measured or
calculated and adds them as a new line to the SNAPSHOT.TXT file. If the file does not exist, it is
automatically created. Each line in the SNAPSHOT file starts with a unique date+time stamp. The file
format is CSV, so it is possible to import the file into a spreadsheet.

2.2.4

CLEAR:

When pressed, CLEAR resets all calculated statistics values back to zero and restarts the run time
counter.

2.2.5

START:

When pressed, START does three functions in one go:
(1) perform a CLEAR
(2) start Recording (if automatic recording is enabled)
(3) activate the relay
START is ideal to conduct measurements that perform recording such as discharge or charge of
batteries

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Other Menus

There are just two menu levels, the main menu and everything else. The normal way of operating is to
select a sub menu from the main menu and when finished, a short press of the BACK button returns to
the main menu. There is no way to go from one sub menu directly to another, so to go from LIMITS to

Main

Run

Setup

Limits

Calibration

(shortcut to RUN menu by long-press of BACK button)

Figure 6: Menu levels
SETUP you must first return to MAIN. The one exception to that rule is that a long press of the BACK
button in each sub menu goes directly to the RUN menu.

Figure 7 shows a detailed map of all sub menus and their options.

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Main:
Run

Limits

run
menu

Relay

Record

on/off
select

(to
Limits)
Setup:

Show

Default

show
menu

Show
Limits:

Clear

Load

Cal

Off
on/off
select

(to
Setup)
RecOpt

ARec

Sampls

Shunts

on/off
select

option
select

on/off
select

sample
select

shunt
select

Save

(back to main)

(to
Calibration)

Volts

show
menu

Calibration:

Setup

HiVolt

LoVolt

HiAmps

LoAmps

Time[s]

C [mAh]

E[mWh]

edit
menu

Show

Volts

Cur A

Cur B

Cur C

Cur D

show
menu

cal
menu

Figure 7: Menu structure

2.3.1

Setup:

All changes in setup are automatically saved in SETUP.TXT and restored when the program starts
Show: shows the current setup values without allowing any changes to be made.
Default: resets the setup to default values
Volts: selects which voltage is displayed (and recorded), the supply side (red terminals) or the load side
(yellow or white terminals). The two voltages differ by the voltage drop across the shunt resistor.
•

RecOpt: Allows a choice of recording options. They are

•

RecChg: records only changes of more than 10mV in voltage or 1mA in currently

•

RecFast: records every measurement and thus produces very large files very quickly.

•

Rec 1s ...Rec5min: records at regular time intervals from one every second to on every 5
minutes.

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Arec: Automatic recording (on / off). When selected on the START button in the RUN menu will also
start recording
Sampls: Selects the number of samples taken and averaged by the INA219 chip. Higher sample rates,
reduce noise but also slow down the measurements
Shunt: selects a different shunt resistor (and its calibration data)

2.3.2

Limits:

Limits can be saved and loaded from LIMITS.TXT but this is not done automatically. By default there
are no limits set.
Show: shows the current limit values without allowing any changes to be made.
Clear: deletes all limits in memory (not in LIMITS.TXT)
Load: loads all limits from LIMITS.TXT
Save: saves the current limits to LIMITS.TXT, overwriting any previously saved values.
HiVolts: allows setting of a high voltage limit. A long press of SEL activates or deactivates the
checking for this limit. If HiVolts is set and active, the relay is deactivated if the voltage exceeds the
limit. Note: HiVolts must be greater than LoVolts
LoVolts: allows setting of a low voltage limit. A long press of SEL activates or deactivates the
checking for this limit. If LoVolts is set and active, the relay is deactivated if the voltage falls below the
limit. Note: HiVolts must be greater than LoVolts
HiAmps: allows setting of a high current limit. A long press of SEL activates or deactivates the
checking for this limit. If HiAmps is set and active, the relay is deactivated if the current exceeds the
limit. Note: HiAmps must be greater than LoAmps
LoAmps allows setting of a low current limit. A long press of SEL activates or deactivates the
checking for this limit. If LoAmps is set and active, the relay is deactivated if the current falls below
the limit. Note: HiAmps must be greater than LoAmps
Time: allows setting of a time limit. A long press of SEL activates or deactivates the checking for this
limit. If Time is set and active, the relay is deactivated if the run time exceeds the limit.
C[mAh]: allows setting of a capacity limit. A long press of SEL activates or deactivates the checking
for this limit. If C[mAh] is set and active, the relay is deactivated if the capacity exceeds the limit.

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E[mWh]: allows setting of an energy limit. A long press of SEL activates or deactivates the checking
for this limit. If E[mWh] is set and active, the relay is deactivated if the energy exceeds the limit.

2.3.3

Calibration:

Calibration values are saved in the CALDATA.TXT file. Voltage calibration is independent of the shunt
resistor but current calibration works only on the selected shunt (SETUP-SHUNT)
Show: shows the current calibration values without allowing any changes to be made. These values
sometimes but not always very small. To be able to show anything meaningful in the limited space, the
program uses a notation that employs m (milli), u micro), and n(nano) notation if necessary.
Volts: allows the calibration of the voltage range. Calibration uses 2 steps, a low target and a high
target. For each step a reference instrument must be used to ensure that the applied voltage matches the
target value. Once that is confirmed using the SEL button, Powermon calculates the required
calibration values, applies them and stores them in CALDATA.TXT.

CurA .. CurD: allows the calibration of the 4 current ranges. It uses the same 2 step process as
described above except that now target currents are use.

Source and data files

Table 4: Source and data files
Name

Content

Expected location

Buttons.py

Handling of buttons (keypad)

~/INA

Cal.py

Calibration dialog

~/INA

CALDATA.TXT

Stores shunts and calibration data

~/INA

CommonDefs.py

Common definitions across all Powermon
modules

~/INA

Display.py

Run menu and display conversions

~/INA

Edit.py

Dialog allowing editing of numbers

~/INA

INA219.py

Handles the INA219 chip

~/INA

LCDpanel.py

Handles the LCD panel

~/INA

LIMITS.TXT

Saved limits

~/INA

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Name

Content

Expected location

Measure.py

Calculates statistics and loads and saves files
(SETUP.TXT, CALDATA.TXT)

~/INA

Menu.py

Dialog for selecting options from a list

~/INA

Powermon.py

Main program and all menus except run menu

~/INA

Recording.py

Handles recording in CSV format

~/INA

Relay.py

Handles the relay output

~/INA

SETUP.TXT

Stores the setup data

~/INA

Show.py

Dialog to show values but not to edit them.

~/INA

SNAPSHOT.TXT

Snapshot data (automatically created)

~/INA/Rec

REC_yyyymmddhhmmss.csv Recording file (automatically created).
“yyyymmdd” is year, month,day, “hhmmss” is
hour, minute, sec

~/INA/Rec

powermon.service

/lib/systemd/system/

Service description to automatically start
powermon at boot

Installation

On Raspberry Pi, as user Pi,
•

create directory INA, i.e. /home/pi/INA and

•

subdirectory Rec i.e. /home/pi/INA/Rec

In Raspberry Pi configuration menu:
•

enable SSH and I2C (and VNC if you want to use it)

•

setup networking (Wifi) to be able to remote login and get your recording files.

Install Adafruit GPIO library
Install Adarfruit-Blinka
Install Adafruit-CircuitPython-CharLCD
Copy all python files and text files to /home/pi/INA
copy file powermon.service to /lib/systemd/system/
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change permissions:
sudo chmod 644 /lib/systemd/system/powermon.service

configure systemd:
sudo systemctl daemon-reload
sudo systemctl enable powermon.service
sudo reboot

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