Introduction

The GY-271 HMC5883L is a 3-axis digital compass module featuring the Honeywell HMC5883L magnetometer IC. With 1° to 2° heading accuracy and a resolution up to 5 milli-gauss, it's ideal for navigation systems, robotics, and orientation detection applications.

Key Features

Technical Specifications

Pin Configuration

Pin	Label	Description	Arduino Connection
1	VCC	Power (3.3V recommended)	3.3V
2	GND	Ground	GND
3	SCL	I2C Clock	A5 (Uno) or SCL
4	SDA	I2C Data	A4 (Uno) or SDA
5	DRDY	Data Ready (Optional)	Any digital pin

Wiring Diagram (Arduino Uno)

// Basic Connections:
// VCC → 3.3V (use regulator if needed)
// GND → GND
// SCL → A5 (or SCL)
// SDA → A4 (or SDA)
// DRDY → (optional interrupt pin)

Basic Compass 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("Could not find HMC5883L");
    while(1);
  }
}

void loop() {
  sensors_event_t event; 
  mag.getEvent(&event);
  
  float heading = atan2(event.magnetic.y, event.magnetic.x);
  float declinationAngle = 0.22; // Adjust for your location
  heading += declinationAngle;
  
  // Correct for when signs are reversed
  if(heading < 0) heading += 2*PI; if(heading > 2*PI) heading -= 2*PI;
  
  float headingDegrees = heading * 180/M_PI;
  
  Serial.print("Heading: ");
  Serial.print(headingDegrees);
  Serial.println("°");
  delay(500);
}

Advanced Configuration

// Set measurement range (default ±1.3 Ga)
mag.setRange(HMC5883_RANGE_1_3GA); 
// Other options: 1.9GA, 2.5GA, 4.0GA, 4.7GA, 5.6GA, 8.1GA

// Set output data rate (default 15Hz)
mag.setDataRate(HMC5883_DATARATE_15HZ);
// Other options: 0.75, 1.5, 3, 7.5, 30, 75, 220Hz

// Set continuous measurement mode
mag.setMeasurementMode(HMC5883_CONTINUOUS);
// Other options: SINGLE (power saving), IDLE

// Hard iron calibration offsets
mag.setOffset(-10.35, 58.95, -40.59); 
// Obtain values from calibration routine

Troubleshooting