GY-273 HMC5883L 3 Axis Module Magnetic Field Sensor

heading = atan2(Y, X) × (180 / π)

/*
  GY-273 HMC5883L Compass Basic Read Example
*/

#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_HMC5883_U.h>

Adafruit_HMC5883_Unified mag = Adafruit_HMC5883_Unified(12345);

void setup() {
  Serial.begin(9600);
  
  if (!mag.begin()) {
    Serial.println("HMC5883L sensor not found! Check wiring.");
    while (1);
  }
  
  // Set measurement range
  mag.setRange(HMC5883L_RANGE_1_3GA);
  
  // Set measurement mode
  mag.setMeasurementMode(HMC5883L_CONTINUOUS);
  
  // Set data rate (15 Hz)
  mag.setDataRate(HMC5883L_DATARATE_15_HZ);
  
  Serial.println("GY-273 HMC5883L Ready");
  Serial.println("-----------------------------");
}

void loop() {
  sensors_event_t event;
  mag.getEvent(&event);
  
  // Magnetic field readings in microteslas (µT)
  // Convert to Gauss by dividing by 100 (1 Gauss = 100 µT)
  float x = event.magnetic.x / 100.0;
  float y = event.magnetic.y / 100.0;
  float z = event.magnetic.z / 100.0;
  
  // Calculate heading in degrees (0° = North)
  float heading = atan2(y, x) * 180 / PI;
  if (heading < 0) heading += 360;
  
  Serial.print("X: "); Serial.print(x);
  Serial.print(" G, Y: "); Serial.print(y);
  Serial.print(" G, Z: "); Serial.print(z);
  Serial.print(" G  |  Heading: ");
  Serial.println(heading);
  
  delay(100);
}

/*
  GY-273 Manual I2C Read Example
*/

#include <Wire.h>

#define HMC5883L_ADDR 0x1E
#define CONFIG_A_REG  0x00
#define CONFIG_B_REG  0x01
#define MODE_REG      0x02
#define DATA_REG_BEGIN 0x03

void setup() {
  Serial.begin(9600);
  Wire.begin();
  
  // Initialize HMC5883L
  Wire.beginTransmission(HMC5883L_ADDR);
  Wire.write(CONFIG_A_REG);
  Wire.write(0x70);  // 8 samples averaged, 15 Hz output rate
  Wire.endTransmission();
  
  Wire.beginTransmission(HMC5883L_ADDR);
  Wire.write(CONFIG_B_REG);
  Wire.write(0xA0);  // ±1.3 Gauss range, gain 1090 LSB/Gauss
  Wire.endTransmission();
  
  Wire.beginTransmission(HMC5883L_ADDR);
  Wire.write(MODE_REG);
  Wire.write(0x00);  // Continuous measurement mode
  Wire.endTransmission();
  
  Serial.println("GY-273 Manual Mode Ready");
}

void loop() {
  // Request 6 bytes of data (X, Y, Z as 16-bit each)
  Wire.beginTransmission(HMC5883L_ADDR);
  Wire.write(DATA_REG_BEGIN);
  Wire.endTransmission();
  Wire.requestFrom(HMC5883L_ADDR, 6);
  
  if (Wire.available() >= 6) {
    int16_t x = Wire.read() << 8 | Wire.read();
    int16_t z = Wire.read() << 8 | Wire.read();  // Note: Z is third
    int16_t y = Wire.read() << 8 | Wire.read();  // Y is fourth
    // (The register order is X, Z, Y)
    
    // Convert to Gauss (using ±1.3G range: 1090 LSB/G)
    float fx = x / 1090.0;
    float fy = y / 1090.0;
    float fz = z / 1090.0;
    
    float heading = atan2(fy, fx) * 180 / PI;
    if (heading < 0) heading += 360;
    
    Serial.print("Heading: ");
    Serial.println(heading);
  }
  
  delay(100);
}

attachInterrupt(digitalPinToInterrupt(DRDY_PIN), dataReadyISR, FALLING);