TI_INA226_micropython

MicroPython driver for the TI INA226 current / power monitor IC.

Datasheet and IC info: https://www.ti.com/product/INA226

This library was originally derived from https://github.com/robert-hh/INA219 and adapted for INA226.

Key points (INA226 specifics)

• Shunt voltage LSB is 2.5 µV/bit (signed register).
• Bus voltage LSB is 1.25 mV/bit (unsigned register).
• To read current and power, you must set the calibration register. Without calibration, the chip’s CURRENT/POWER registers are not valid.

Driver overview

The driver provides:

• configure(...) for conversion timing / averaging / operating mode
• calibrate(...) for calibration register + current/power scaling
• Properties:
  • bus_voltage (V)
  • shunt_voltage (V)
  • current (A) and current_mA (mA)
  • power (W) and power_mW (mW)

Installation / files

• ina226.py — the driver
• ina_calc_conf.py — interactive helper to build a config register value and print a ready-to-paste configure() call

Configuration register

INA226 configuration register layout (high-level):

CONFIG = CONST_BITS + AVG + VBUSCT + VSHCT + MODE

Where:

• AVG controls averaging (1..1024 samples)
• VBUSCT is bus voltage conversion time
• VSHCT is shunt voltage conversion time
• MODE selects triggered/continuous shunt/bus conversions

The driver exposes constants like:

• INA226.AVG_512
• INA226.VBUSCT_588US
• INA226.VSHCT_588US
• INA226.MODE_SHUNT_BUS_CONTINUOUS

Calibration (auto-calculation)

The driver can compute calibration values automatically.

You must provide:

• r_shunt_ohms (your shunt resistor value in ohms)
• and either:
  • max_expected_amps (recommended)
  • or current_lsb_a (advanced; choose a “nice” LSB)

How it works (summary)

• Choose current_lsb_a (amps/bit). Default:
  • current_lsb_a = max_expected_amps / 32768
• Compute calibration register:
  • cal_value = 0.00512 / (r_shunt_ohms * current_lsb_a)
• Power LSB is fixed relationship:
  • power_lsb_w = 25 * current_lsb_a

Example (ESP / generic MicroPython)

import ina226
from machine import Pin, I2C

# Adjust pins for your board
i2c = I2C(scl=Pin(2), sda=Pin(0))

ina = ina226.INA226(i2c, addr=0x40)

# Optional: configure conversion behavior (defaults are already reasonable)
ina.configure(
    avg=ina226.INA226.AVG_512,
    vbusct=ina226.INA226.VBUSCT_588US,
    vshct=ina226.INA226.VSHCT_588US,
    mode=ina226.INA226.MODE_SHUNT_BUS_CONTINUOUS,
)

# Auto-calibrate (recommended)
ina.calibrate(r_shunt_ohms=0.1, max_expected_amps=3.6)

print("Bus voltage:", ina.bus_voltage, "V")
print("Shunt voltage:", ina.shunt_voltage, "V")
print("Current:", ina.current, "A")
print("Power:", ina.power, "W")

# Or convenience in mA / mW
print("Current:", ina.current_mA, "mA")
print("Power:", ina.power_mW, "mW")

Using a “nice” rounded current LSB (optional)

If you want a specific current resolution (example: 100 µA/bit):

ina.calibrate(r_shunt_ohms=0.1, max_expected_amps=3.6, current_lsb_a=0.0001)

Troubleshooting

• If current / power raises “not calibrated”: call calibrate(...).
• After brown-outs / resets the INA226 may clear the calibration register; the driver automatically re-applies it when reading current/power.