Powermon Guide Rev1 0

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1 Description
2 Usage
3 Source and data files
4 Installation

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
 1  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  0..20VDC in 10 mV resolution 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 Yes

Current Always: upper right Yes Yes

Power Selectable field Yes Yes

Capacity Selectable field Yes Yes

Energy Selectable field Yes Yes

Run time Selectable field Yes 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 - - Yes

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2 Usage

2.1 Scenarios

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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Charger + -

battery

Powermon

Figure 1: Measuring charge into a battery

+ -

battery

Powermon

Figure 2: Measuring battery capacity

+ -

battery

Powermon

shunt

Figure 3: Using an external shunt

Powermon Guide Rev. 1.0 03/10/2019

2.2 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

The button assignments in the run menu are shown in Table 3

Table 3: Button assignments in the Run Menu

PREV SEL NEXT BACK

Short

press

cycle through field options

for the LEFT field

SNAPSHOT cycle through field options

for the RIGHT field

Return to main menu

Long

press

In manual range:

decrements range

Toggles between auto and

manual range mode

In manual range:

increments range

in auto range: CLEAR

START

2.2.1 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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Voltage Current

LEFT

FIELD

RIGHT

FIELD

Auto or Manual range

and range values

shunt volt range:

Auto Man

40 mV: A a

80 mV: B b

160mV: C c

320mV: D d

Figure 4: Run Menu display

Powermon Guide Rev. 1.0 03/10/2019

(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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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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R : Recording ON

- : Recording OFF

L : Volt = load side

S : Volt = supply side

: no limit set

: hi limit set

: lo limit set

: hi+lo limits set

Blink = limit reached

High (max) Energy limit

High (max) Capacity limit

High (max) Time limit

High / Low Current limits

High / Low Voltage limits

Figure 5: Run Menu display with status

Powermon Guide Rev. 1.0 03/10/2019

2.3 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

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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Figure 6: Menu levels

Main

Run Setup Limits Calibration

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

Powermon Guide Rev. 1.0 03/10/2019

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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Figure 7: Menu structure

Run Limits Relay Record Setup Off

Show Clear Load Save HiVolt LoVolt HiAmps LoAmps Time[s] C [mAh] E[mWh]

Show Default Volts Shunts

Main:

Limits:

Setup:

on/off

select

on/off

select

on/off

select

run

on/off

select

shunt

select

show

(to

Setup)

(to

Limits)

(back to main)

show

edit

RecOpt

option

select

Cal

(to

Calibration)

Sampls

sample

select

ARec

on/off

select

Show Volts Cur A

show

cal

Cur B

cal

Cur C

cal

Cur D

cal

Calibration:

Powermon Guide Rev. 1.0 03/10/2019

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.

3 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 Service description to automatically start

powermon at boot

/lib/systemd/system/

4 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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