One of the important pieces of information that might be useful for your robot, it if is going to plan its own path, is its direction of travel. So, let's learn how to hook up a digital compass to the Raspberry Pi.

There are several chips that provide digital compass capability; one of the most common is the HMC5883L 3-Axis Digital Compass chip. This chip is packaged onto a module by several companies, but almost all of them result in a similar interface. The following is a picture of one the GY-271 HMC5883L Triple Axis Compass Magnetometer Sensor Module, which is available from a number of online retailers:

This type of digital compass uses magnetic sensors to discover the earth's magnetic field. The output of these sensors is then made accessible to the outside world through a set of registers that allow the user to set things such as the sample rate, and continuous or single sampling. The x, y, and z directions are output-using registers...