TinyCompass

/*
TinyDuino Compass Demo

This example code is in the public domain.

January 26, 2015 by Tony Batey

https://tiny-circuits.com/

*/
#include <Wire.h>

#define Addr 0x1E               // 7-bit address of HMC5883 compass

void setup() {
  Serial.begin(9600);
  delay(100);                   // Power up delay
  Wire.begin();
  
  // Set operating mode to continuous
  Wire.beginTransmission(Addr); 
  Wire.write(byte(0x02));
  Wire.write(byte(0x00));
  Wire.endTransmission();
}
int x_max=-10000;  // Starting values for hard iron calibration
int y_max=-10000;  // We want these values to be extreme in the 
int x_min=10000;   // opposite direction so it calibrates nicely
int y_min=10000;

void loop() {
  int x, y, z;

  // Initiate communications with compass
  Wire.beginTransmission(Addr);
  Wire.write(byte(0x03));       // Send request to X MSB register
  Wire.endTransmission();

  Wire.requestFrom(Addr, 6);    // Request 6 bytes; 2 bytes per axis
  if(Wire.available() <=6) {    // If 6 bytes available
    x = Wire.read() << 8 | Wire.read();
    z = Wire.read() << 8 | Wire.read();
    y = Wire.read() << 8 | Wire.read();
  }
  
  // Print raw values
  Serial.print("X=");
  Serial.print(x);
  Serial.print(", Y=");
  Serial.print(y);
  Serial.print(", Z=");
  Serial.print(z);
  
  if(x > x_max) //Find values of hard iron distortion
    x_max = x;  //This will store the max and min values
  if(y >y_max)	//of the magnetic field around you
    y_max = y;
  if(y<y_min)
    y_min = y;
  if(x<x_min)
    x_min = x;
  
  //Print max and min values
  Serial.print(", Xmax=");
  Serial.print(x_max);
  Serial.print(", Ymax=");
  Serial.print(y_max); 
  Serial.print(", Xmin=");
  Serial.print(x_min);
  Serial.print(", Ymin=");
  Serial.print(y_min);
  
  int xoffset= (x_max+x_min)/2;
  int yoffset= (y_max+y_min)/2;
  
  int x_scale = x-xoffset; // Math to compensate for hard 
  int y_scale = y-yoffset; // iron distortions
  
  // Heading in radians
  float heading = atan2(x_scale,y_scale); 
  
  //Heading between 0 and 6.3 radians
  if(heading < 0)
    heading += 2*PI;
    
  if(heading>2*PI)
    heading -= 2*PI;
  
  //Conversion to degrees  
  int Degrees = heading * 180/M_PI; 
  
  
  Serial.print("Heading (degrees): "); Serial.print(Degrees);
  
  int LED = Degrees/17; //Led shield has 21 Leds. Dividing 360 by
  						//17 will give us values from 0 to 21
  						
  if (LED==0)	 		//since there is no Led 0, we will turn	
    LED=21;				//Led 21 on instead
   
  LedOn(LED);
  Serial.print("LED: "); Serial.println(LED);
  
  delay(40);
}

//Function to turn on the led indicated in the main loop
void LedOn(int ledNum)
{
  for(int i=4;i<10;i++)
  {
    pinMode(i, INPUT);
    digitalWrite(i, LOW);
  };
  if(ledNum<1 || ledNum>21) return;
  char highpin[21]={6,7,6,8,5,8,8,7,9,7,9,8,5,9,6,9,9,5,6,5,7};
  char lowpin[21]= {7,6,8,6,8,5,7,8,7,9,8,9,9,5,9,6,4,6,5,7,5};

  ledNum--;
  digitalWrite(highpin[ledNum],HIGH);
  digitalWrite(lowpin[ledNum],LOW);
  pinMode(highpin[ledNum],OUTPUT);
  pinMode(lowpin[ledNum],OUTPUT);
}