test.ino

#include <Wire.h> //I2C Arduino Library

#define addr 0x0D //I2C Address for The HMC5883

void setup() {

  Serial.begin(9600);
  Wire.begin();


  Wire.beginTransmission(addr); //start talking
  Wire.write(0x0B); // Tell the HMC5883 to Continuously Measure
  Wire.write(0x01); // Set the Register
  Wire.endTransmission();
  Wire.beginTransmission(addr); //start talking
  Wire.write(0x09); // Tell the HMC5883 to Continuously Measure
  Wire.write(0x1D); // Set the Register
  Wire.endTransmission();
}

void loop() {

  int x, y, z; //triple axis data

  //Tell the HMC what regist to begin writing data into


  Wire.beginTransmission(addr);
  Wire.write(0x00); //start with register 3.
  Wire.endTransmission();

  //Read the data.. 2 bytes for each axis.. 6 total bytes
  Wire.requestFrom(addr, 6);
  if (6 <= Wire.available()) {
    x = Wire.read(); //MSB  x
    x |= Wire.read() << 8; //LSB  x
    z = Wire.read(); //MSB  z
    z |= Wire.read() << 8; //LSB z
    y = Wire.read(); //MSB y
    y |= Wire.read() << 8; //LSB y
  }

  // Show Values
  Serial.print("X Value: ");
  Serial.println(x);
  Serial.print("Y Value: ");
  Serial.println(y);
  Serial.print("Z Value: ");
  Serial.println(z);
  Serial.println();

  delay(500);
}