Micromag 3 Axis

Here’s some modified code from Sensor Workshop to get heading values in Arduino from the Micromag 3 axis magneto sensor. Next up, accelerometer calculations on the magneto sensor to get tilt compensation on the compass readings.

//heading calcuations added from Daniel's processing code to get a heading value of 0-3600 in Arduino
//edited by Che-Wei Wang
//tested on MICROMAG 3-AXIS V1.00
//clockwise rotation is positive

//Original Arduino code for controlling a MicroMag3 magnetometer through SPI
//by Daniel Soltis

#define SCLK 7 //the clock to pulse (#1 on breakout)
#define MISO 6 //master in, slave out (#2 on breakout)
#define MOSI 5 //master out, slave in (#3 on breakout)
#define SSNOT 4 //when low, the device is enabled (#4 on breakout)
#define DRDY 3 //this is low after a reset, high when data is ready (#5 on breakout)
#define RESET 2 //this needs to be toggled low-high-low before each measurement (#6 on breakout)

#include <math.h>

int x = 0;
int y = 0;
int z = 0;
int heading = 0;

void setup(){
  Serial.begin(9600);

  pinMode(SSNOT, OUTPUT);
  pinMode(RESET, OUTPUT);
  pinMode(MOSI, OUTPUT);
  pinMode(MISO, INPUT);
  pinMode(DRDY, INPUT);
  pinMode(SCLK, OUTPUT);

  //i could just ground this line, but this at least marks it as
  //something that one could change if needed
  digitalWrite(SSNOT, LOW);
}

void loop(){

  x=readaxis(0);
  y=readaxis(1);
  z=readaxis(2);
  getHeading(x,y,z);

}

void send_bit(int _high){

  //this sends the bit on the rising edge of the clock

  digitalWrite(MOSI, _high);
  delay(2);
  digitalWrite(SCLK, HIGH);
  delay(2);
  digitalWrite(SCLK, LOW);
  delay(2);
}

int receive_bit(){

  //this receives 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){
  //this function sends eight bits, waits until the data is ready
  //and receives 16 bits

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

  //send the command byte

  //this sends data that we are not in debug mode
  //and sets the amount of time to read the magnetic sensors (the ASIC period)
  //as /2048
  send_bit(LOW);
  send_bit(HIGH);
  send_bit(HIGH);
  send_bit(LOW);
  send_bit(LOW);
  send_bit(LOW);

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

  //wait until the drdy line is high
  while (digitalRead(DRDY) == LOW){
    //wait
    //Serial.println("waiting");
  }
  //Serial.println("data!");

  long runningtotal = 0;

  //receive the results and tally them up as they come in 

  //the leftmost bit signs the number as positive or negative
  long sign = receive_bit();

  //the remaining bits need to be translated from individual bits into an integer
  for (int i = 14; i >= 0; i = i - 1){
    long thisbit = receive_bit();
    thisbit = thisbit << i;
    runningtotal = runningtotal | thisbit;
  }

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

  //this sends the data over the serial line, as a string separated by commas
  if (_axis == 0){
    x = runningtotal;
    Serial.print(x,DEC);
    Serial.print(44, BYTE);
  }
  else if (_axis == 1){
    y = runningtotal;
    Serial.print(y,DEC);
    Serial.print(44, BYTE);
  }
  else{
    z = runningtotal;
    Serial.print(z,DEC);
    Serial.print(44, BYTE);
  }
  return runningtotal;
}

int getHeading(float x, float y, float z){
  int heading=0;
  if (x==0 && y<0) heading=900.0;
  if(x==0 && y>0) heading=2700.0;
  if (x < 0) heading = (PI - atan(y/x))/TWO_PI*3600.0;
  if (x > 0 && y < 0) heading = (-1*atan(y/x))/TWO_PI*3600.0;
  if (x > 0 && y > 0) heading = (2.0*PI - atan(y/x))/TWO_PI*3600.0;
  Serial.print("heading: ");
  Serial.println(int(heading));
  return heading;
}