INA219 with ESP32: DC Current, Voltage & Power

Measure the DC voltage, current and power of a small load with an INA219 breakout. The tutorial separates the low-voltage I2C connection from the load-current path so that the measurement circuit is clear.

Identify the shunt and terminals

Check that the board really uses INA219 and identify VCC, GND, SDA, SCL, VIN+ and VIN−. The large resistor in the measurement path is the shunt. This example uses the driver's standard calibration for a 0.1 Ω shunt, usually marked R100. If your resistor differs, use a calibration appropriate to that resistance instead of assuming the current reading is correct.

Prepare a small DC test

The example controller is an ESP32-C3 Supermini with free, exposed GPIO6 and GPIO7. First confirm that its serial/upload test works. Select ESP32C3 Dev Module and enable USB CDC On Boot for native USB. Open Serial Monitor at 115200 baud. Disconnect power before changing wires.

Start with a current-limited low-voltage supply and a modest known load. Keep the load within the breakout's resistor, connector and thermal ratings. The sensor's measured bus limit is 26 V; a library preset with “32V” in its name does not increase that hardware limit.

Connect I2C and the load path

These are explicitly assigned GPIO numbers for this C3 example, not physical header positions or universal ESP32 defaults. For another controller, choose free pins from its own pinout and change Wire.begin() in the sketch. Keep the first test on short wires with one peripheral.

Current flows through VIN+ → shunt → VIN− → load. VCC powers the measurement electronics; it is not the load-current input. Do not connect VIN+ and VIN− across a supply as though they were a voltage-meter pair: that would place the low-resistance shunt directly across it.

Install the INA219 driver

In Arduino Library Manager install Adafruit INA219 and Adafruit BusIO. Accept the listed dependencies. Create a new sketch, paste the complete example, click Verify, then Upload. Keep a record of your board profile and library versions when reporting an issue.

The starting address is 0x40. Address solder links can change it; inspect those links and use an I2C scan before changing the code. Verify common ground before applying load power.

Read voltage, current and power

The sketch reports bus voltage at VIN−, shunt voltage, current in mA and calculated power in mW. These units differ by factors of 1,000; label any saved data accordingly. Upload before switching the load on.

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

Adafruit_INA219 powerMonitor(0x40);
void setup() {
  Serial.begin(115200);
  delay(1500);
  Wire.begin(6, 7);
  if (!powerMonitor.begin(&Wire)) {
    Serial.println("INA219 not found.");
    while (true) delay(1000);
  }
  // Only for the standard 0.1-ohm (R100) shunt.
  powerMonitor.setCalibration_32V_2A();
}
void loop() {
  const float busV = powerMonitor.getBusVoltage_V();
  const float shuntMv = powerMonitor.getShuntVoltage_mV();
  const float currentMa = powerMonitor.getCurrent_mA();
  const float milliwatts = powerMonitor.getPower_mW();
  if (!powerMonitor.success()) {
    Serial.println("I2C read failed; check wiring.");
  } else {
    Serial.printf("VIN-: %.3f V | Shunt: %.3f mV | Current: %.2f mA | Power: %.2f mW\n",
      busV, shuntMv, currentMa, milliwatts);
  }
  delay(1000);
}

Validate with one known load

1. Switch the load off and note the near-zero current baseline.
2. Switch on a modest load and confirm that current rises.
3. Compare the load voltage and current against an independent meter or an expected resistor calculation.
4. Check the shunt value and calibration if readings differ by a consistent scale factor.

Reversing the current path reverses the sign. Bus voltage is measured on the load side; adding the shunt drop estimates the supply-side voltage. The shunt adds a small voltage drop of its own, so place it deliberately in the power path you intend to characterize.

Troubleshooting

References and further reading

• Adafruit INA219 wiring guide
• INA219 Arduino driver
• TI INA219 product documentation
• ESP32 I2C API

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