This is the fourth tutorial of a series of tutorials where I show you how to connect Grove sensors and Components to an Arduino and to get started for a robot project using these sensors. In the last few instructables, I showed how to get started with I2C Motor Driver, Single Axis Analog Gyro and a Thumb Joystick, also check that out if you are here for the robot build.

In this tutorial I'm going to show you how to get started with a Grove three Axis Digital Compass with an Arduino.

So lets get started.....

Step 1: Tools and Components

All that you need for this tutorial is-

Arduino UNO
Grove 3 Axis Digital Compass
Jumper wires

Note- No soldering skills are required to build this project, but it is good to know how to solder there are a good soldering tutorials on YouTube that can help you get started.

Step 2: Getting Started

I2C is a is 2 pin communication system the 2 lines are the SDA (data line) and SCL (clock line), this reduces the number of pins of the Arduino dedicated to drive the Digital Compass. There is a good documentation of Arduino I2C in the Arduino website, you can read to that to get started with I2C.

Step 3: Hardware

Now time for the connections the Arduino has the SCL line on analog pin 5 and SDA line on analog pin 4.

Here is how you need to connect he hardware -

Arduino analog pin 5 - Grove I2C Motor Driver SCL
Arduino analog pin 4 - Grove I2C Motor Driver SDA
Arduino +5V - Grove I2C Motor Driver VCC
Arduino Gnd - Grove I2C Motor Driver Gnd

After you connect the hardware it is time to upload the code......

Step 4: Code

The code is quite simple and all it does is reads the compass readings and prints it out on a serial monitor. The Compass calibrates for a few seconds when you run the code make sure not to rotate or disturb the compass while this happens and after it completes you should get a fine stream of data from the sensor.

<p>// Reference the I2C Library<br>#include <wire.h>
// Reference the HMC5883L Compass Library
#include <hmc5883l.h></hmc5883l.h></wire.h></p><p>// Store our compass as a variable.
HMC5883L compass;
// Record any errors that may occur in the compass.
int error = 0;</p><p>// Out setup routine, here we will configure the microcontroller and compass.
void setup()
{
  // Initialize the serial port.
  Serial.begin(9600);</p><p>  Serial.println("Starting the I2C interface.");
  Wire.begin(); // Start the I2C interface.</p><p>  Serial.println("Constructing new HMC5883L");
    
  Serial.println("Setting scale to +/- 1.3 Ga");
  error = compass.setScale(1.3); // Set the scale of the compass.
  if(error != 0) // If there is an error, print it out.
    Serial.println(compass.getErrorText(error));
  
  Serial.println("Setting measurement mode to continous.");
  error = compass.setMeasurementMode(MEASUREMENT_CONTINUOUS); // Set the measurement mode to Continuous
  if(error != 0) // If there is an error, print it out.
    Serial.println(compass.getErrorText(error));
}</p><p>// Our main program loop.
void loop()
{
  // Retrive the raw values from the compass (not scaled).
  MagnetometerRaw raw = compass.readRawAxis();
  // Retrived the scaled values from the compass (scaled to the configured scale).
  MagnetometerScaled scaled = compass.readScaledAxis();
  
  // Values are accessed like so:
  int MilliGauss_OnThe_XAxis = scaled.XAxis;// (or YAxis, or ZAxis)</p><p>  // Calculate heading when the magnetometer is level, then correct for signs of axis.
  float heading = atan2(scaled.YAxis, scaled.XAxis);
  
  // Once you have your heading, you must then add your 'Declination Angle', which is the 'Error' of the magnetic field in your location.
  // Find yours here: http://www.magnetic-declination.com/
  // Mine is: -2��37' which is -2.617 Degrees, or (which we need) -0.0456752665 radians, I will use -0.0457
  // If you cannot find your Declination, comment out these two lines, your compass will be slightly off.
  float declinationAngle = -0.0457;
  heading += declinationAngle;
  
  // Correct for when signs are reversed.
  if(heading < 0)
    heading += 2*PI;
    
  // Check for wrap due to addition of declination.
  if(heading > 2*PI)
    heading -= 2*PI;
   
  // Convert radians to degrees for readability.
  float headingDegrees = heading * 180/M_PI; </p><p>  // Output the data via the serial port.
  Output(raw, scaled, heading, headingDegrees);</p><p>  // Normally we would delay the application by 66ms to allow the loop
  // to run at 15Hz (default bandwidth for the HMC5883L).
  // However since we have a long serial out (104ms at 9600) we will let
  // it run at its natural speed.
  delay(66);//of course it can be delayed longer.
}</p><p>// Output the data down the serial port.
void Output(MagnetometerRaw raw, MagnetometerScaled scaled, float heading, float headingDegrees)
{
   Serial.print("Raw:\t");
   Serial.print(raw.XAxis);
   Serial.print("   ");   
   Serial.print(raw.YAxis);
   Serial.print("   ");   
   Serial.print(raw.ZAxis);
   Serial.print("   \tScaled:\t");
   
   Serial.print(scaled.XAxis);
   Serial.print("   ");   
   Serial.print(scaled.YAxis);
   Serial.print("   ");   
   Serial.print(scaled.ZAxis);</p><p>   Serial.print("   \tHeading:\t");
   Serial.print(heading);
   Serial.print(" Radians   \t");
   Serial.print(headingDegrees);
   Serial.println(" Degrees   \t");
}</p>