ESP32-WROOM-32D
Adafruit INA219 breakout board w/ R020 (0.020) Shunt

• MAX Current = 10A
• MAX Voltage = 32VDC
• Shunt Resistor = 0.020

I’m measuring a +24VDC Load, however, INA219 is only reading roughly 5VDC.

Connections are Source to +Vin and Load to -Vin. SCL, SDA, VS, GND on module are all connected correctly.

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

// Custom definition for 12-bit resolution with 8 samples (4.156 ms conversion time)
#define INA219_CONFIG_BADCRES_12BIT_8S_4MS 0x0078 // Manually defined

// Shunt resistor value
const float shuntResistorValue = 0.02; // 20 milli-ohms
const float maxCurrent = 10.0;          // Max current 10A

// Addresses for INA219 sensors
const uint8_t ina219Addresses[] = {0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4A, 0x4B, 0x4C, 0x4D, 0x4E, 0x4F};
const int NUM_SENSORS = sizeof(ina219Addresses) / sizeof(ina219Addresses[0]);

Adafruit_INA219 ina219[NUM_SENSORS];
bool sensorInitialized[NUM_SENSORS];

// Custom function to write to INA219 register via I2C
void writeINA219Register(uint8_t address, uint8_t reg, uint16_t value) {
    Wire.beginTransmission(address);
    Wire.write(reg);                         // Register to write to
    Wire.write((value >> 8) & 0xFF);         // MSB
    Wire.write(value & 0xFF);                // LSB
    Wire.endTransmission();
}

// Custom calibration function for 32V, 320mV gain, 10A max, and 0.020 mOhm shunt
void setCustomCalibration(uint8_t address) {
    // Calculate the current LSB (Least Significant Bit)
    // Current LSB = MaxExpected_I / 32767 (Max 15-bit value)
    float currentLSB = maxCurrent / 32767.0; // In amperes per bit
    currentLSB = 0.000305;                   // 305 µA per bit for easier calibration

    // Calculate the calibration value
    // Calibration = trunc(0.04096 / (currentLSB * shuntResistorValue))
    uint16_t calValue = (uint16_t)(0.04096 / (currentLSB * shuntResistorValue));

    // Write the calibration register (0x05)
    writeINA219Register(address, 0x05, calValue);

    // Configuration register setup: 32V range, 320mV gain, continuous mode
    uint16_t configValue = INA219_CONFIG_BVOLTAGERANGE_32V |
                           INA219_CONFIG_GAIN_8_320MV |
                           INA219_CONFIG_BADCRES_12BIT |
                           INA219_CONFIG_SADCRES_12BIT_16S_8510US |
                           //INA219_CONFIG_BADCRES_12BIT_8S_4MS |
                           INA219_CONFIG_BADCRES_12BIT_64S_34MS |
                           // Custom averaging 12-bit, 8 samples, 4ms
                           INA219_CONFIG_MODE_SANDBVOLT_CONTINUOUS;

    // Write the configuration register (0x00)
    writeINA219Register(address, 0x00, configValue);
    

    Serial.print("Custom calibration applied for INA219 at 0x");
    Serial.println(address, HEX);
}

void setup() {
    Serial.begin(115200);
    Wire.begin();

    for (int i = 0; i < NUM_SENSORS; i++) {
        Serial.print("Initializing INA219 at 0x");
        Serial.print(ina219Addresses[i], HEX);
        ina219[i] = Adafruit_INA219(ina219Addresses[i]);

        if (ina219[i].begin()) {
            sensorInitialized[i] = true;
            Serial.println(" - Initialized");
            setCustomCalibration(ina219Addresses[i]); // Apply custom calibration
        } else {
            sensorInitialized[i] = false;
            Serial.println(" - Failed to initialize");
        }
    }
    delay(2000); // Allow time for initialization
}

void readINA219Sensors() {
    for (int i = 0; i < NUM_SENSORS; i++) {
        if (sensorInitialized[i]) {
            float shuntVoltage_mV = ina219[i].getShuntVoltage_mV(); // Shunt voltage in mV
            float busVoltage_V = ina219[i].getBusVoltage_V();       // Bus voltage in V
            float current_mA = ina219[i].getCurrent_mA();           // Current in mA
            float power_mW = ina219[i].getPower_mW();               // Power in mW
            float loadvoltage = busVoltage_V + (shuntVoltage_mV / 1000.0);

            // Output the readings to the Serial console
            Serial.print("Sensor ");
            Serial.print(i + 1);
            Serial.print(" at 0x");
            Serial.print(ina219Addresses[i], HEX);
            Serial.print(": Bus Voltage = ");
            Serial.print(busVoltage_V);
            Serial.print(" V, Shunt Voltage = ");
            Serial.print(shuntVoltage_mV);
            Serial.print(" mV, Load Voltage = ");
            Serial.print(loadvoltage);
            Serial.print(" V, Current = ");
            Serial.print(current_mA);
            Serial.print(" mA, Power = ");
            Serial.print(power_mW);
            Serial.println(" mW");
        }
    }
    delay(1000); // Delay between readings
}

void loop() {
    readINA219Sensors();
}

This is just a unit test for the module. The code base integrates many modules and has worked as expected before. However, this is a unit test created for INA219 module validation. At this point I’ve completely isolated the INA219 module from the rest of the system. So only the ESP32-WROOM-32D and INA219 module are connected.