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_24_arduSerie_Arduino_Compass.ino

/* Arduino Compass 
 * 
 * by Dejan Nedelkovski, 
 * www.HowToMechatronics.com
 * 
 */
#include <Wire.h> //I2C Arduino Library
#define Magnetometer_mX0 0x03 
#define Magnetometer_mX1 0x04 
#define Magnetometer_mZ0 0x05 
#define Magnetometer_mZ1 0x06 
#define Magnetometer_mY0 0x07 
#define Magnetometer_mY1 0x08 
int mX0, mX1, mX_out;
int mY0, mY1, mY_out;
int mZ0, mZ1, mZ_out;
float heading, headingDegrees, headingFiltered, declination;
float Xm,Ym,Zm;
#define Magnetometer 0x1E //I2C 7bit address of HMC5883
void setup(){
    //Initialize Serial and I2C communications
    Serial.begin(115200);
    Wire.begin();
    delay(100);
 
    Wire.beginTransmission(Magnetometer); 
    Wire.write(0x02); // Select mode register
    Wire.write(0x00); // Continuous measurement mode
    Wire.endTransmission();
}
void loop(){
 
    // — — X-Axis
    Wire.beginTransmission(Magnetometer); // transmit to device
    Wire.write(Magnetometer_mX1);
    Wire.endTransmission();
    Wire.requestFrom(Magnetometer,1); 
    if(Wire.available()<=1) 
   {
    mX0 = Wire.read();
   }
    Wire.beginTransmission(Magnetometer); // transmit to device
    Wire.write(Magnetometer_mX0);
    Wire.endTransmission();
    Wire.requestFrom(Magnetometer,1); 
    if(Wire.available()<=1) 
   {
    mX1 = Wire.read();
   }
    // — — Y-Axis
    Wire.beginTransmission(Magnetometer); // transmit to device
    Wire.write(Magnetometer_mY1);
    Wire.endTransmission();
    Wire.requestFrom(Magnetometer,1); 
    if(Wire.available()<=1) 
   {
    mY0 = Wire.read();
   }
    Wire.beginTransmission(Magnetometer); // transmit to device
    Wire.write(Magnetometer_mY0);
    Wire.endTransmission();
    Wire.requestFrom(Magnetometer,1); 
    if(Wire.available()<=1) 
   {
    mY1 = Wire.read();
   }
 
    // — — Z-Axis
    Wire.beginTransmission(Magnetometer); // transmit to device
    Wire.write(Magnetometer_mZ1);
    Wire.endTransmission();
    Wire.requestFrom(Magnetometer,1); 
    if(Wire.available()<=1) 
   {
    mZ0 = Wire.read();
   }
    Wire.beginTransmission(Magnetometer); // transmit to device
    Wire.write(Magnetometer_mZ0);
    Wire.endTransmission();
    Wire.requestFrom(Magnetometer,1); 
    if(Wire.available()<=1) 
   {
    mZ1 = Wire.read();
   }
 
    // — — X-Axis
       mX1=mX1<<8;
       mX_out =mX0+mX1; // Raw data
    // From the datasheet: 0.92 mG/digit
       Xm = mX_out*0.00092; // Gauss unit
    //* Earth magnetic field ranges from 0.25 to 0.65 Gauss, so these are     
    //the values that we need to get approximately.
    // — — Y-Axis
       mY1=mY1<<8;
       mY_out =mY0+mY1;
       Ym = mY_out*0.00092;
    // — — Z-Axis
       mZ1=mZ1<<8;
       mZ_out =mZ0+mZ1;
       Zm = mZ_out*0.00092;
    // ==============================
    //Calculating Heading
       heading = atan2(Ym, Xm);
 
    // Correcting the heading with the declination angle depending on your 
    // location
    // You can find your declination angle at:  
    // http://www.ngdc.noaa.gov/geomag-web/
    // At my location it’s 4.2 degrees => 0.073 rad
    // My city = -12.44 degrees = > -0.19540706305329 rad
    //  http://www.magnetic-declination.com/
    // declination = 0.073; 
       declination = -0.195; 
       heading += declination;
    // Correcting when signs are reveresed
       if(heading <0) heading += 2*PI;
    // Correcting due to the addition of the declination angle
       if(heading > 2*PI)heading -= 2*PI;
       headingDegrees = heading * 180/PI; // The heading in Degrees unit
    // Smoothing the output angle / Low pass filter 
       headingFiltered = headingFiltered*0.85 + headingDegrees*0.15;
    //Sending the heading value through the Serial Port to Processing IDE
       Serial.println(headingFiltered);
 
       delay(50);
}