A compass is a handy addition for your car so you'll always know which direction you're facing without having to rely on GPS. A lot of cars come with a compass built in, but if yours doesn't, Instructables user DaAwesomeP shows you how to make your own. The project uses an Arduino Pro Mini, a small magnetometer, a little OLED screen and a handful of other parts. By the end, you can just plug the compass into your car's cigarette lighter and be on your way.
DIY Digital Compass [Instructables]