| micromag 3-axis magnetic field sensor Demonstrates the use of micromag 3-axis magnetic field sensor The sensor communicates using the ISP protocol. Based on Daniel Soltis example. Created 28 April 2008 |

    // micromag 3-axis magnetic field sensor

    int SCLK = 8;  // magnetometer pin 1
    int MISO = 9;  // magnetometer pin 2
    int MOSI = 10;  // magnetometer pin 3
    int SSNOT = 11;  // magnetometer pin 4
    int DRDY = 12;  // magnetometer pin 5
    int RESET = 13;  // magnetometer pin 6
    int x = 0;  // magnetic field x axis
    int y = 0;  // magnetic field y axis
    int z = 0;  // magnetic field z axis
    int heading = 0;  // magnetic field heading

    void setup() {
      Serial.begin(9600);
      pinMode(48, OUTPUT);  // turn ON the board LED for diagnostics only
      digitalWrite(48, HIGH);
      pinMode(SSNOT, OUTPUT);
      pinMode(RESET, OUTPUT);
      pinMode(MOSI, OUTPUT);
      pinMode(SCLK, OUTPUT);
      pinMode(MISO, INPUT);
      pinMode(DRDY, INPUT);
      digitalWrite(SSNOT, LOW);
    }

    void loop() {
      x = readAxis(0);  // read the x-axis magnetic field value
      y = readAxis(1);  // read the y-axis magnetic field value
      z = readAxis(2);  // read the z-axis magnetic field value
      heading = getHeading(x, y, z);  // calculates the magnetic field heading
      Serial.print("x: ");
      Serial.print(x, DEC);
      Serial.print("y: ");
      Serial.print(y, DEC);
      Serial.print("z: ");
      Serial.print(z, DEC);
      Serial.print("heading: ");
      Serial.print(heading, DEC);
      delay(20000);  // next reading in 20 seconds
    }

    // specific commands for the sensor

    void sendBit(int bit){
      // send the bit on the RISING edge of the clock
      digitalWrite(MOSI, bit);
      delay(2);
      digitalWrite(SCLK, HIGH);
      delay(2);
      digitalWrite(SCLK, LOW);
      delay(2);
    }

    int receiveBit(){
      // receive the data on the FALLING edge of the clock
      digitalWrite(SCLK, HIGH);
      delay(2);
      int bit = digitalRead(MISO);
      delay(2);
      digitalWrite(SCLK, LOW);
      delay(2);
      return bit;
    }

    float readAxis(int axis){
      // send eight bits, wait until the data is ready then receive 16 bits

      // pulse the reset
      digitalWrite(RESET, LOW);
      delay(2);
      digitalWrite(RESET, HIGH);
      delay(2);
      digitalWrite(RESET, LOW);
      delay(2);

      // send the command byte
      // set the time to read the magnetic sensors (ASIC period) as /2048
      sendBit(LOW);
      sendBit(HIGH);
      sendBit(HIGH);
      sendBit(LOW);
      sendBit(LOW);
      sendBit(LOW);

      // the last two bits select the axis
      if (axis == 0){ // x axis
        sendBit(LOW);
        sendBit(HIGH);
      }
      else if (axis == 1){ // y axis
        sendBit(HIGH);
        sendBit(LOW);
      }
      else{ // z axis
        sendBit(HIGH);
        sendBit(HIGH);
      }

      // wait until the DRDY line is high
      while(digitalRead(DRDY) == LOW) {
      }

      long total = 0;

      // receive result
      // the leftmost bit mark the number as positive or negative
      long sign = receiveBit();

      // the remaining bits are converted to an integer
      for (int i = 14; i >= 0; i = i - 1){
        long thisbit = receiveBit();
        thisbit = thisbit << i;
        total = total | thisbit;
      }

      if(sign == 1) {
        total = total - 32768;
      }

      // set and return the appropriate variable
      if (axis == 0){
        x = total;
      }
      else if (axis == 1){
        y = total;
      }
      else{
        z = total;
      }
      return total;
    }

    int getHeading(float x, float y, float z){
      float heading=0;
      if((x == 0)&&(y < 0))
        heading= PI/2.0;
      if((x == 0)&&(y > 0))
        heading=3.0*PI/2.0;
      if (x < 0)
        heading = PI - atan(y/x);
      if((x > 0)&&(y < 0))
        heading = -atan(y/x);
      if((x > 0)&&(y > 0))
        heading = 2.0*PI - atan(y/x);
      return  int(degrees(heading));
    }

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