INA219 / INA226 Voltage, Current and Power Sensor Complete Guide

The INA219 and INA226 are Texas Instruments current and power monitors. They measure the small voltage across a shunt resistor in series with a load, and the voltage of the supply line, then report current, bus voltage and power over I2C. They measure low-voltage DC: how much a battery pack, a solar panel or a 3.3 V or 5 V rail really draws. That is a different job from the BL0937 and BL0942 energy-meter chips, which measure mains AC power.

This guide compares the two chips with the real datasheet numbers, shows the pins, the 16 possible I2C addresses, how to wire the shunt, how to calibrate for current, and the mistakes that give wrong readings. The chip data comes from the TI datasheets for the INA219 and the INA226. Breakout boards differ from seller to seller, so check the labels on your own board.

INA219 or INA226

The INA219 handles more current with a small shunt because of its gain stage: with a 0.1 Ω shunt and the 320 mV range it measures up to 3.2 A. The INA226 has no gain stage, so its range is fixed at 81.92 mV: with a 0.1 Ω shunt that is about 0.8 A. For higher currents use a smaller shunt. The INA226 has finer resolution, a higher bus voltage limit and an alert output. Both have 16 addresses, so one I2C bus can monitor many rails.

Source: Texas Instruments datasheets for the INA219 and the INA226.

Getting started

Specifications

Source: Texas Instruments datasheets for the INA219 and the INA226.

Dimensions

The INA219 comes in an SOT-23-8 package of 1.63 × 2.90 mm and an SOIC-8 package of 3.91 × 4.90 mm. Breakout boards come in many sizes and shunt values, so measure your own board before you design a case. The shunt on most hobby boards is 0.1 Ω, but check the marking: R100 means 0.1 Ω.

Source: package data in the INA219 datasheet. Board sizes are not given.

Pins

The order of the header pins differs between boards, so read the print on yours.

Source: pin descriptions in the TI datasheets.

Wiring to an ESP32

The chip measures on the high side, so the shunt sits in the positive wire. The ground of the measured supply and the ground of the ESP32 must be connected, otherwise readings are noise. Breakouts have 3.3 V or 5 V logic: use the 3.3 V logic level for an ESP32.

I2C addresses

Both chips have two address pins, A0 and A1. Each can go to GND, VS, SDA or SCL, which gives 16 combinations from 0x40 to 0x4F. With both pins at GND the address is 0x40, which is what nearly all breakouts use by default. Many boards have solder jumpers to change it. If the sensor is not found, run an I2C scan.

#include <Wire.h>
void setup() {
  Serial.begin(115200);
  Wire.begin(21, 22);
  for (uint8_t a = 0x40; a <= 0x4F; a++) {
    Wire.beginTransmission(a);
    if (Wire.endTransmission() == 0) Serial.printf("Found 0x%02Xn", a);
  }
}
void loop() {}

Source: address tables in the TI datasheets.

Software setup

Read the INA219

#include <Wire.h>
#include <Adafruit_INA219.h>

Adafruit_INA219 ina219;

void setup() {
  Serial.begin(115200);
  Wire.begin(21, 22);
  if (!ina219.begin()) {
    Serial.println("Failed to find INA219");
    while (1) delay(10);
  }
}

void loop() {
  float busVoltage = ina219.getBusVoltage_V();
  float current_mA = ina219.getCurrent_mA();
  float power_mW = ina219.getPower_mW();

  Serial.print("Bus Voltage: "); Serial.print(busVoltage); Serial.println(" V");
  Serial.print("Current: "); Serial.print(current_mA); Serial.println(" mA");
  Serial.print("Power: "); Serial.print(power_mW); Serial.println(" mW");

  delay(1000);
}

I did not run this sketch on a board, it follows the Adafruit library example. The library assumes a 0.1 Ω shunt and a 32 V, 2 A range by default. If your shunt differs, call setCalibration_16V_400mA() or the other calibration functions.

Read the INA226 yourself

The INA226 is easy to read with a few register accesses. Register 0x01 holds the shunt voltage (2.5 µV per bit, signed), 0x02 the bus voltage (1.25 mV per bit), 0x04 the current and 0x03 the power. The current and power registers only work after you write the calibration register 0x05, where CAL = 0.00512 / (Current_LSB × R_shunt). The power LSB is 25 times the Current_LSB.

#include <Wire.h>
#define ADDR 0x40
const float R_SHUNT = 0.1f;          // ohm
const float CURRENT_LSB = 0.0001f;   // 0.1 mA per bit

uint16_t rd(uint8_t reg) {
  Wire.beginTransmission(ADDR);
  Wire.write(reg);
  Wire.endTransmission(false);
  Wire.requestFrom(ADDR, 2);
  return (Wire.read() << 8) | Wire.read();
}
void wr(uint8_t reg, uint16_t v) {
  Wire.beginTransmission(ADDR);
  Wire.write(reg); Wire.write(v >> 8); Wire.write(v & 0xFF);
  Wire.endTransmission();
}

void setup() {
  Serial.begin(115200);
  Wire.begin(21, 22);
  Serial.printf("Manufacturer ID 0x%04X (expect 0x5449)n", rd(0xFE));
  wr(0x05, (uint16_t)(0.00512f / (CURRENT_LSB * R_SHUNT)));   // 512
}

void loop() {
  float vbus = rd(0x02) * 0.00125f;                    // volt
  float amps = (int16_t)rd(0x04) * CURRENT_LSB;        // ampere
  float watt = rd(0x03) * 25.0f * CURRENT_LSB;         // watt
  Serial.printf("%.3f V  %.4f A  %.3f Wn", vbus, amps, watt);
  delay(500);
}

With a 0.1 Ω shunt the full scale is 0.8192 A, so a Current_LSB of 0.1 mA is right. Do not exceed that current through the shunt, or the readings clip. The INA226 also reports a manufacturer ID of 0x5449 and a die ID of 0x2260, which is a good way to check the wiring. This sketch has not been run on a board.

Source: Texas Instruments INA226 datasheet, registers and calibration.

Getting accurate readings

• Pick the shunt for the current. The voltage across the shunt must stay inside the range of the chip: 81.92 mV for the INA226, up to 320 mV for the INA219. A 0.1 Ω shunt is for amps, a 0.01 Ω shunt for tens of amps.
• Use the whole range. A tiny current on a big shunt gives few bits. Choose the shunt so the highest current you expect uses most of the range.
• Calibrate against a multimeter. Shunt resistors have a tolerance. Measure a known current once and correct the Current_LSB.
• Wire the shunt with Kelvin sense. Run the VIN+ and VIN− wires from the shunt pads, not from the thick power wires, so the wire resistance does not count.
• Average fast loads. A motor or a radio draws spikes. Set averaging, or take many readings and average, to get a stable number.
• Keep the logic supply clean. Put a 0.1 µF capacitor near VS.

Real gotchas

• The voltage limit is hard. Do not apply more than 26 V (INA219) or 36 V (INA226) to the input pins. This is a stress limit, not a rating for normal use, and spikes from motors and relays count.
• The INA219 has 16 addresses, not 4. Both chips have two address pins with four states each.
• No calibration, no current. The current and power registers read zero until the calibration register is written. The shunt and bus voltage registers work at once.
• The shunt is in the high side. If you wire it in the ground line you break the common ground with the ESP32 and the readings are meaningless.
• Both grounds must meet. The measured supply and the ESP32 need a common ground.
• Negative current is possible. The current register is signed. Cast it to a signed 16-bit value.
• The shunt dissipates power. Check P = I² × R, especially with small shunts and large currents.
• Not for mains. These chips are for low-voltage DC only. For AC mains use an isolated energy-meter module, never these.

Compared with other options

See the BL0937 and BL0942 guides for mains power. The ACS712 row is general knowledge and not from a datasheet read for this guide.

What to build with it

• Battery fuel gauging: track real current draw to estimate remaining runtime.
• Solar panel monitoring: measure actual power output under real conditions.
• Power-budget debugging: find which part of a project is drawing more current than expected.
• Overcurrent protection logic: cut power in software if current exceeds a safe threshold.

• A USB power meter that logs voltage and current of a charger or a cable.
• A bench supply logger that records the current of a device under test.

Safety notes

Conclusion

The INA219 and the INA226 give you voltage, current and power of a DC line over I2C. Take the INA219 for a wide gain range and currents of a few amps with a small shunt, and the INA226 for a 36 V bus, better resolution and an alert output. Remember the two traps: the current register stays at zero until you calibrate, and the shunt must sit in the high side with a common ground.

Chip data is from the Texas Instruments datasheets for the INA219 and the INA226.