I bought this little circuit below, to be connected to the Arduino, thinking be an accelerometer. Is not! Is a sensor which measures the magnetic field in three axes and sends it to the Arduino. Even I was disappointed, I found it interesting too!
Comes with a Terminal bar, You can dock and test even without welding. On the Board see the connectors 3V3, DRDY, SDA, SDL, GND and 5V. More information about how to connect to the Arduino can be found This link.
There is an indication of X and Y axes to mount the magnetic sensors in the right direction. The z-axis is logically upward!
When properly connected, the sensor measures, in micro teslas, the magnetic field in the direction X, Y and Z.
Very interesting, Although is still looking for practical use in addition to serving as a compass. Those interested can follow the links below:
Buy the sensor – http://www.buyincoins.com/item/36433.html
More information about how to connect to the Arduino – https://learn.adafruit.com/adafruit-hmc5883l-breakout-triple-axis-magnetometer-compass-sensor/wiring-and-test