HMC5883L 3-Axis Magnetometer

1. Introduction

The HMC5883L is a 3-axis magnetometer that measures magnetic field strength to determine compass heading. It's widely used in navigation systems, drones, robots, and any application that needs to know which direction is North.

The sensor detects Earth's magnetic field and outputs values for all three axes, which can be converted into a compass heading (0-360°).

2. Technical Specifications

Understanding Magnetic Declination

Magnetic North (where the compass points) differs from True North (geographic North Pole). The difference is called magnetic declination and varies by location.

To get accurate True North heading, you must add your local declination angle. Find yours at: NOAA Magnetic Declination Calculator

3. Wiring Guide

Figure 1: HMC5883L I2C wiring with ESP32

4. Project: Digital Compass

Required Library

Install Adafruit HMC5883 Unified via Arduino Library Manager.

Complete Compass Code

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

Adafruit_HMC5883_Unified mag = Adafruit_HMC5883_Unified(12345);

// Set your local magnetic declination (in radians)
// Example: Dubai is about +2.5 degrees = 0.0436 radians
float declinationAngle = 0.0436;

void setup() {
    Serial.begin(115200);
    Serial.println("HMC5883L Digital Compass");

    if (!mag.begin()) {
        Serial.println("ERROR: HMC5883L not found!");
        Serial.println("If using QMC5883L, use different library");
        while (1);
    }

    Serial.println("Compass Ready!");
}

void loop() {
    sensors_event_t event;
    mag.getEvent(&event);

    // Calculate heading from X and Y components
    float heading = atan2(event.magnetic.y, event.magnetic.x);

    // Add magnetic declination
    heading += declinationAngle;

    // Normalize to 0-2π range
    if (heading < 0) heading += 2 * PI;
    if (heading > 2 * PI) heading -= 2 * PI;

    // Convert to degrees
    float headingDegrees = heading * 180.0 / PI;

    // Display heading with cardinal direction
    Serial.print("Heading: ");
    Serial.print(headingDegrees, 1);
    Serial.print("° - ");
    Serial.println(getCardinalDirection(headingDegrees));

    delay(250);
}

String getCardinalDirection(float heading) {
    if (heading >= 337.5 || heading < 22.5) return "N";
    if (heading >= 22.5 && heading < 67.5) return "NE";
    if (heading >= 67.5 && heading < 112.5) return "E";
    if (heading >= 112.5 && heading < 157.5) return "SE";
    if (heading >= 157.5 && heading < 202.5) return "S";
    if (heading >= 202.5 && heading < 247.5) return "SW";
    if (heading >= 247.5 && heading < 292.5) return "W";
    return "NW";
}

Expected Output

HMC5883L Digital Compass
Compass Ready!
Heading: 45.2° - NE
Heading: 44.8° - NE
Heading: 90.1° - E
Heading: 180.3° - S

5. Calibration

For accurate readings, the sensor needs calibration to compensate for nearby magnetic interference (called "hard iron" and "soft iron" distortion).

Simple Calibration Method

1. Rotate the sensor slowly in a full circle
2. Record the min and max values for X and Y axes
3. Calculate offsets: offset = (max + min) / 2
4. Subtract offsets from readings

6. Applications

• Drone navigation: Heading hold and waypoint navigation
• Robot orientation: Autonomous navigation
• GPS enhancement: Heading when GPS course unavailable
• Augmented reality: Direction-based overlays
• Weather stations: Wind direction relative to North

7. Troubleshooting

Sensor not detected

• Check if it's actually QMC5883L (address 0x0D)
• Run I2C scanner to verify address

Heading jumps erratically

• Move away from metal objects and magnets
• Keep away from motors and speakers
• Calibrate the sensor

Reading stuck at one value

• Strong magnetic field nearby (speaker, magnet)
• Sensor may be damaged

8. Summary

• 3-axis magnetometer for compass heading
• I2C address: 0x1E (HMC5883L) or 0x0D (QMC5883L)
• Apply magnetic declination for true North
• Keep away from magnetic interference
• Calibrate for best accuracy