pi-ina219 1.4.1

Description:

piina219 1.4.1

This Python library supports the
INA219 voltage,
current and power monitor sensor from Texas Instruments on both Python 2
and 3. The intent of the library is to make it easy to use the quite
complex functionality of this sensor.
The library currently only supports continuous reads of voltage and
power, but not triggered reads.
The library supports the detection of overflow in the current/power
calculations which results in meaningless values for these readings.
The low power mode of the INA219 is supported, so if only occasional
reads are being made in a battery based system, current consumption can
be minimised.
The library has been tested with the Adafruit INA219
Breakout.

Installation and Upgrade
This library and its dependency (Adafruit GPIO
library) can be
installed from PyPI by executing:
sudo pip3 install pi-ina219
To upgrade from a previous version installed direct from Github execute:
sudo pip3 uninstall pi-ina219
sudo pip3 install pi-ina219
The Adafruit library supports the I2C protocol on all versions of the
Raspberry Pi. Remember to enable the I2C bus under the Advanced
Options of raspi-config.


Usage
The address of the sensor unless otherwise specified is the default of
0x40.
Note that the bus voltage is that on the load side of the shunt
resistor, if you want the voltage on the supply side then you should add
the bus voltage and shunt voltage together, or use the
supply_voltage() function.

I2C Bus number
In most cases this will be determined automatically, however if this
fails you will see the exception:
Could not determine default I2C bus for platform
In this case just set the bus number in the INA219 constructor, for
example:
ina = INA219(SHUNT_OHMS, busnum=1)
This is known to be required with Raspberry Pi 4 and the ‘Bullseye’
(October 2021) Raspberry Pi OS.


Simple - Auto Gain
This mode is great for getting started, as it will provide valid
readings until the device current capability is exceeded for the value
of the shunt resistor connected (3.2A for 0.1Ω shunt resistor). It does
this by automatically adjusting the gain as required until the maximum
is reached, when a DeviceRangeError exception is thrown to avoid
invalid readings being taken.
The downside of this approach is reduced current and power resolution.
#!/usr/bin/env python
from ina219 import INA219
from ina219 import DeviceRangeError

SHUNT_OHMS = 0.1


def read():
ina = INA219(SHUNT_OHMS)
ina.configure()

print("Bus Voltage: %.3f V" % ina.voltage())
try:
print("Bus Current: %.3f mA" % ina.current())
print("Power: %.3f mW" % ina.power())
print("Shunt voltage: %.3f mV" % ina.shunt_voltage())
except DeviceRangeError as e:
# Current out of device range with specified shunt resistor
print(e)


if __name__ == "__main__":
read()


Advanced - Auto Gain, High Resolution
In this mode by understanding the maximum current expected in your
system and specifying this in the script you can achieve the best
possible current and power resolution. The library will calculate the
best gain to achieve the highest resolution based on the maximum
expected current.
In this mode if the current exceeds the maximum specified, the gain will
be automatically increased, so a valid reading will still result, but at
a lower resolution.
As above when the maximum gain is reached, an exception is thrown to
avoid invalid readings being taken.
#!/usr/bin/env python
from ina219 import INA219
from ina219 import DeviceRangeError

SHUNT_OHMS = 0.1
MAX_EXPECTED_AMPS = 0.2


def read():
ina = INA219(SHUNT_OHMS, MAX_EXPECTED_AMPS)
ina.configure(ina.RANGE_16V)

print("Bus Voltage: %.3f V" % ina.voltage())
try:
print("Bus Current: %.3f mA" % ina.current())
print("Power: %.3f mW" % ina.power())
print("Shunt voltage: %.3f mV" % ina.shunt_voltage())
except DeviceRangeError as e:
# Current out of device range with specified shunt resistor
print(e)


if __name__ == "__main__":
read()


Advanced - Manual Gain, High Resolution
In this mode by understanding the maximum current expected in your
system and specifying this and the gain in the script you can always
achieve the best possible current and power resolution, at the price of
missing current and power values if a current overflow occurs.
#!/usr/bin/env python
from ina219 import INA219
from ina219 import DeviceRangeError

SHUNT_OHMS = 0.1
MAX_EXPECTED_AMPS = 0.2


def read():
ina = INA219(SHUNT_OHMS, MAX_EXPECTED_AMPS)
ina.configure(ina.RANGE_16V, ina.GAIN_1_40MV)

print("Bus Voltage: %.3f V" % ina.voltage())
try:
print("Bus Current: %.3f mA" % ina.current())
print("Power: %.3f mW" % ina.power())
print("Shunt voltage: %.3f mV" % ina.shunt_voltage())
except DeviceRangeError as e:
print("Current overflow")


if __name__ == "__main__":
read()


Sensor Address
The sensor address may be altered as follows:
ina = INA219(SHUNT_OHMS, MAX_EXPECTED_AMPS, address=0x41)


Low Power Mode
The sensor may be put in low power mode between reads as follows:
ina.configure(ina.RANGE_16V)
while True:
print("Voltage : %.3f V" % ina.voltage())
ina.sleep()
time.sleep(60)
ina.wake()
Note that if you do not wake the device after sleeping, the value
returned from a read will be the previous value taken before sleeping.



Functions

INA219() constructs the class. The arguments, are:

shunt_ohms: The value of the shunt resistor in Ohms (mandatory).
max_expected_amps: The maximum expected current in Amps
(optional).
busnum: The I2C bus number for the device platform, defaults to
auto detects 0 or 1 for Raspberry Pi or Beaglebone Black
(optional).
address: The I2C address of the INA219, defaults to 0x40
(optional).
log_level: Set to logging.INFO to see the detailed calibration
calculations and logging.DEBUG to see register operations
(optional).


configure() configures and calibrates how the INA219 will take
measurements. The arguments, which are all optional, are:

voltage_range: The full scale voltage range, this is either 16V or
32V, represented by one of the following constants (optional).

RANGE_16V: Range zero to 16 volts
RANGE_32V: Range zero to 32 volts (default). Device only
supports up to 26V.


gain: The gain, which controls the maximum range of the shunt
voltage, represented by one of the following constants (optional).

GAIN_1_40MV: Maximum shunt voltage 40mV
GAIN_2_80MV: Maximum shunt voltage 80mV
GAIN_4_160MV: Maximum shunt voltage 160mV
GAIN_8_320MV: Maximum shunt voltage 320mV
GAIN_AUTO: Automatically calculate the gain (default)


bus_adc: The bus ADC resolution (9, 10, 11, or 12-bit), or set the
number of samples used when averaging results, represented by one
of the following constants (optional).

ADC_9BIT: 9 bit, conversion time 84us.
ADC_10BIT: 10 bit, conversion time 148us.
ADC_11BIT: 11 bit, conversion time 276us.
ADC_12BIT: 12 bit, conversion time 532us (default).
ADC_2SAMP: 2 samples at 12 bit, conversion time 1.06ms.
ADC_4SAMP: 4 samples at 12 bit, conversion time 2.13ms.
ADC_8SAMP: 8 samples at 12 bit, conversion time 4.26ms.
ADC_16SAMP: 16 samples at 12 bit, conversion time 8.51ms
ADC_32SAMP: 32 samples at 12 bit, conversion time 17.02ms.
ADC_64SAMP: 64 samples at 12 bit, conversion time 34.05ms.
ADC_128SAMP: 128 samples at 12 bit, conversion time 68.10ms.


shunt_adc: The shunt ADC resolution (9, 10, 11, or 12-bit), or set
the number of samples used when averaging results, represented by
one of the following constants (optional).

ADC_9BIT: 9 bit, conversion time 84us.
ADC_10BIT: 10 bit, conversion time 148us.
ADC_11BIT: 11 bit, conversion time 276us.
ADC_12BIT: 12 bit, conversion time 532us (default).
ADC_2SAMP: 2 samples at 12 bit, conversion time 1.06ms.
ADC_4SAMP: 4 samples at 12 bit, conversion time 2.13ms.
ADC_8SAMP: 8 samples at 12 bit, conversion time 4.26ms.
ADC_16SAMP: 16 samples at 12 bit, conversion time 8.51ms
ADC_32SAMP: 32 samples at 12 bit, conversion time 17.02ms.
ADC_64SAMP: 64 samples at 12 bit, conversion time 34.05ms.
ADC_128SAMP: 128 samples at 12 bit, conversion time 68.10ms.




voltage() Returns the bus voltage in volts (V).
supply_voltage() Returns the bus supply voltage in volts (V).
This is the sum of the bus voltage and shunt voltage. A
DeviceRangeError exception is thrown if current overflow occurs.
current() Returns the bus current in milliamps (mA). A
DeviceRangeError exception is thrown if current overflow occurs.
power() Returns the bus power consumption in milliwatts (mW). A
DeviceRangeError exception is thrown if current overflow occurs.
shunt_voltage() Returns the shunt voltage in millivolts (mV). A
DeviceRangeError exception is thrown if current overflow occurs.
current_overflow() Returns ‘True’ if an overflow has occured.
Alternatively handle the DeviceRangeError exception as shown in the
examples above.
sleep() Put the INA219 into power down mode.
wake() Wake the INA219 from power down mode.
reset() Reset the INA219 to its default configuration.
is_conversion_ready() check if conversion was done before reading
the next measurement results.



Performance
On a Raspberry Pi 2 Model B running Raspbian Jesse and reading a 12-bit
voltage in a loop, a read occurred approximately every 10 milliseconds.
On a Raspberry Pi 4 running Raspbian Buster a read occurred
approximately every 570 microseconds.


Debugging
To understand the calibration calculation results and automatic gain
increases, informational output can be enabled with:
ina = INA219(SHUNT_OHMS, log_level=logging.INFO)
Detailed logging of device register operations can be enabled with:
ina = INA219(SHUNT_OHMS, log_level=logging.DEBUG)


Testing
Install the library as described above, this will install all the
dependencies required for the unit tests, as well as the library itself.
Clone the library source from Github then execute the test suite from
the top level directory with:
python3 -m unittest discover -s tests -p 'test_*.py'
A single unit test class may be run as follows:
python3 -m unittest tests.test_configuration.TestConfiguration
Code coverage metrics may be generated and viewed with:
coverage run --branch --source=ina219 -m unittest discover -s tests -p 'test_*.py'
coverage report -m


Coding Standard
This library adheres to the PEP8 standard and follows the idiomatic
style described in the book Writing Idiomatic Python by Jeff Knupp.