A look at the MAG3110 magnetometer

5th February 2019

1966

In this article we look at the MAG3110 magnetometer, we will discuss the sensor and also show how to connect the sensor to a Raspberry Pi and an Arduino with code examples for both

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.

Features

80 Hz maximum sampling rate
I²C interface 400 kHz
-40°C to +85°C operation
0.95 to 3.6-volt supply
Full-scale range ±1000 µT
Low-power, single-shot measurement mode
Noise down to 0.25 µT rms
Sensitivity of 0.10 µµT

Again for ease to use its easier to buy a module with the device fitted to it, here is one that I purchased. You can see the MAG3110 in the middle of the picture

And here is a schematic for a typical MAG3110 module

Parts List

These are the parts that I used for the Raspberry Pi example

Name	Link
Raspberry Pi	2018 new original Raspberry Pi 3 Model B+ (plug) Built-in Broadcom 1.4GHz quad-core 64 bit processor Wifi Bluetooth and USB Port
MAG3110 module	MAG3110 module electronic compass module
Connecting wire	Free shipping Dupont line 120pcs 20cm male to male + male to female and female to female jumper wire

For the Arduino example we used the following parts

Name	Link
Arduino Uno	UNO R3 CH340G/ATmega328P, compatible for Arduino UNO
MAG3110 module	MAG3110 module electronic compass module
Connecting wire	Free shipping Dupont line 120pcs 20cm male to male + male to female and female to female jumper wire

Schematics and Connection

The MAG3110 module being an I2C module is very easy to connect to many microcontrollers, we will show you an Arduino example and a Raspberry Pi example

Arduino connection

Raspberry Pi connection

Arduino Code Example

This code example does not require any libraries

Source code

#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(5);
}
 
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);
}

Testing

Open up the serial monitor

x=44,y=1138,z=1505
x=65175,y=580,z=2037
x=65117,y=745,z=1435
x=65145,y=1487,z=1814
x=64700,y=949,z=1912
x=64848,y=671,z=1921
x=65411,y=803,z=2218
x=64852,y=720,z=1644

Raspberry Pi Code example

Save the following code as mag3110.py

Source code

import smbus
import time
 
bus = smbus.SMBus(1)
 
# MAG3110 I2C address 0x0E
# Select Control register, 0x10(16)
bus.write_byte_data(0x0E, 0x10, 0x01)
 
time.sleep(0.5)
 
# MAG3110 I2C address 0x0E
# Read data back from 0x01(1), 6 bytes
data = bus.read_i2c_block_data(0x0E, 0x01, 6)
 
# Convert the data
xMag = data[0] * 256 + data[1]
if xMag > 32767 :
	xMag -= 65536
 
yMag = data[2] * 256 + data[3]
if yMag > 32767 :
	yMag -= 65536
 
zMag = data[4] * 256 + data[5]
if zMag > 32767 :
	zMag -= 65536
 
# Output data
print "X-Axis : %d" %xMag
print "Y-Axis : %d" %yMag
print "Z-Axis : %d" %zMag