INA226 current and power monitor

The TI INA226 measures current through a real 0.1 ohm shunt, the bus voltage and the power, to 2.5 microvolts, over I2C.

Aliases: CJMCU-226, INA226 module, power meter, current sensor. It is the INA219's more precise sibling, with a bus voltage pin of its own and an alert pin, and the sensor of battery monitors and solar chargers.

Pins

Pin	What it does
VCC, GND	Supply, 2.7 to 5.5 V.
SCL, SDA	I2C. The board carries the pull-ups.
ALERT	Pulls low on the alert chosen in mask/enable.
VBUS	The bus voltage input: tie it to the load's supply side.
IN+, IN-	The two ends of the 0.1 ohm shunt, in series with the load.

Properties

address, 0x40 to 0x4F. There is nothing to drag: the current is whatever the circuit puts through the shunt.

Reading it on an Arduino

With Rob Tillaart's library, which Mokxi ships as INA226.h:

#include "INA226.h"
INA226 INA(0x40);

void setup() {
  Serial.begin(9600);
  Wire.begin();
  INA.begin();
  INA.setMaxCurrentShunt(0.8, 0.1);
}

void loop() {
  Serial.print(INA.getBusVoltage(), 3);
  Serial.print(" V  ");
  Serial.print(INA.getCurrent_mA(), 1);
  Serial.println(" mA");
  delay(1000);
}

Wolfgang Ewald's INA226_WE.h reads it too.

How it talks

Sixteen-bit registers: 0x00 configuration (averaging and conversion times), 0x01 the shunt at 2.5 uV a count, 0x02 the bus at 1.25 mV, 0x03 power, 0x04 current, 0x05 calibration (current and power read zero until it is written), 0x06 mask/enable with the conversion ready flag, 0x07 the alert limit, 0xFE 0x5449 and 0xFF 0x2260. A conversion takes 2.2 ms by default, times the averaging count.

What it does not model

The noise that averaging removes, and the SMBus alert response.

Common mistakes

Leaving VBUS unconnected: the bus voltage and power read zero. Expecting current before the calibration is written: every library writes it in its setup call.