Linkit One and MAG3110 magnetometer example

Freescale’s MAG3110 is a small, low-power, digital 3-axis magnetometer. The device can be used in conjunction with a 3-axis accelerometer to realize an orientation independent electronic compass that can provide accurate heading information. It features a standard I2C serial interface output and smart embedded functions.

The MAG3110 is capable of measuring magnetic fields with an output data rate (ODR) up to 80 Hz; these output data rates correspond to sample intervals from 12.5 ms to several seconds. The MAG3110 is available in a plastic DFN package and it is guaranteed to operate over the extended temperature range of -40°C to +85°C.

Again for ease to use its easier to buy a module, here is one that I purchased

I also found this schematic online of a module

Connection

Layout

Code

This  example  does not require any libraries

[codesyntax lang=”cpp”]

#include <Wire.h>

#define MAG_ADDR  0x0E //7-bit address for the MAG3110, doesn't change

void setup()
{
  Wire.begin();        // join i2c bus (address optional for master)
  Serial.begin(9600);  // start serial for output
  config();            // turn the MAG3110 on
}

void loop()
{
  print_values();
  delay(500);
}

void config(void)
{
  Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E
  Wire.write(0x11);             // cntrl register2
  Wire.write(0x80);             // write 0x80, enable auto resets
  Wire.endTransmission();       // stop transmitting
  delay(15); 
  Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E
  Wire.write(0x10);             // cntrl register1
  Wire.write(1);                // write 0x01, active mode
  Wire.endTransmission();       // stop transmitting
}

void print_values(void)
{
  Serial.print("x=");
  Serial.print(read_x());
  Serial.print(",");  
  Serial.print("y=");    
  Serial.print(read_y());
  Serial.print(",");       
  Serial.print("z=");    
  Serial.println(read_z());
}

int mag_read_register(int reg)
{
  int reg_val;
  
  Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E
  Wire.write(reg);              // x MSB reg
  Wire.endTransmission();       // stop transmitting
  delayMicroseconds(2); //needs at least 1.3us free time between start and stop
  
  Wire.requestFrom(MAG_ADDR, 1); // request 1 byte
  while(Wire.available())    // slave may write less than requested
  { 
    reg_val = Wire.read(); // read the byte
  }
  
  return reg_val;
}

int mag_read_value(int msb_reg, int lsb_reg)
{
  int val_low, val_high;  //define the MSB and LSB
  val_high = mag_read_register(msb_reg);
  delayMicroseconds(2); //needs at least 1.3us free time between start and stop
  val_low = mag_read_register(lsb_reg);
  int out = (val_low|(val_high << 8)); //concatenate the MSB and LSB
  return out;
}

int read_x(void)
{
  return mag_read_value(0x01, 0x02);
}

int read_y(void)
{
  return mag_read_value(0x03, 0x04);
}

int read_z(void)
{
  return mag_read_value(0x05, 0x06);
}

[/codesyntax]

Testing

Open up the serial monitor

x=146,y=1045,z=1958
x=145,y=1043,z=1940
x=146,y=1044,z=1945
x=147,y=1046,z=1958
x=142,y=1041,z=1953
x=149,y=1044,z=1950
x=148,y=1041,z=1948
x=150,y=1049,z=1957
x=148,y=1042,z=1949
x=147,y=1044,z=1943
x=146,y=1042,z=1944
x=151,y=1042,z=1955
x=141,y=1042,z=1937

Link
MAG3110 compass module three-axis electronic compass module magnetoresistive sensor magnetometer module