Usermod INA226

This Usermod is designed to read values from an INA226 sensor and output the following:

Current
Voltage
Power
Shunt Voltage
Overflow status

Configuration

The following settings can be configured in the Usermod Menu:

Enabled: Enable or disable the usermod.
I2CAddress: The I2C address in decimal. Default is 64 (0x40).
CheckInterval: Number of seconds between readings. This should be higher than the time it takes to make a reading, determined by the two next options.
INASamples: The number of samples to configure the INA226 to use for a measurement. Higher counts provide more accuracy. See the 'Understanding Samples and Conversion Times' section for more details.
INAConversionTime: The time to use on converting and preparing readings on the INA226. Higher times provide more precision. See the 'Understanding Samples and Conversion Times' section for more details.
Decimals: Number of decimals in the output.
ShuntResistor: Shunt resistor value in milliohms. An R100 shunt resistor should be written as "100", while R010 should be "10".
CurrentRange: Expected maximum current in milliamps (e.g., 5 A = 5000 mA).
MqttPublish: Enable or disable MQTT publishing.
MqttPublishAlways: Publish always, regardless if there is a change.
MqttHomeAssistantDiscovery: Enable Home Assistant discovery.

Understanding Samples and Conversion Times

The INA226 uses a programmable ADC with configurable conversion times and averaging to optimize the measurement accuracy and speed. The conversion time and number of samples are determined based on the INASamples and INAConversionTime settings. The following table outlines the possible combinations:

Conversion Time (μs)	1 Sample	4 Samples	16 Samples	64 Samples	128 Samples	256 Samples	512 Samples	1024 Samples
140	0.28 ms	1.12 ms	4.48 ms	17.92 ms	35.84 ms	71.68 ms	143.36 ms	286.72 ms
204	0.408 ms	1.632 ms	6.528 ms	26.112 ms	52.224 ms	104.448 ms	208.896 ms	417.792 ms
332	0.664 ms	2.656 ms	10.624 ms	42.496 ms	84.992 ms	169.984 ms	339.968 ms	679.936 ms
588	1.176 ms	4.704 ms	18.816 ms	75.264 ms	150.528 ms	301.056 ms	602.112 ms	1204.224 ms
1100	2.2 ms	8.8 ms	35.2 ms	140.8 ms	281.6 ms	563.2 ms	1126.4 ms	2252.8 ms
2116	4.232 ms	16.928 ms	67.712 ms	270.848 ms	541.696 ms	1083.392 ms	2166.784 ms	4333.568 ms
4156	8.312 ms	33.248 ms	132.992 ms	531.968 ms	1063.936 ms	2127.872 ms	4255.744 ms	8511.488 ms
8244	16.488 ms	65.952 ms	263.808 ms	1055.232 ms	2110.464 ms	4220.928 ms	8441.856 ms	16883.712 ms

It is important to pick a combination that provides the needed balance between accuracy and precision while ensuring new readings within the CheckInterval setting. When USERMOD_INA226_DEBUG is defined, the info pane contains the expected time to make a reading, which can be seen in the table above.

As an example, if you want a new reading every 5 seconds (CheckInterval), a valid combination is 256 samples and 4156 μs which would provide new values every 2.1 seconds.

The picked values also slightly affect power usage. If the CheckInterval is set to more than 20 seconds, the INA226 is configured in triggered reading mode, where it only uses power as long as it's working. Then the conversion time and average samples counts determine how long the chip stays turned on every CheckInterval time.

Calculating Current and Power

The INA226 calculates current by measuring the differential voltage across a shunt resistor and using the calibration register value to convert this measurement into current. Power is calculated by multiplying the current by the bus voltage.

For detailed programming information and register configurations, refer to the INA226 datasheet.

Author

@LordMike

Compiling

To enable, compile with INA226 in custom_usermods (e.g. in platformio_override.ini).

ini

[env:ina226_example]
extends = env:esp32dev
custom_usermods = ${env:esp32dev.custom_usermods} INA226
build_flags = ${env:esp32dev.build_flags}
  ; -D USERMOD_INA226_DEBUG ; -- add a debug status to the info modal