I started with very basic function, showing bearing and heading angle from a digital magnetometer on an LCD, but there are a number of digital and analog pins are left unused on the microcontroller (Arduino compatible, JeonLab mini) so I added a digital temperature sensor and a phototransistor to adjust the brightness of the backlight (single LED) of the LCD.
I still have more than a few pins available and have a plan to add more sensors such as an exterior thermometer, anti-theft device, etc. (any suggestion would be appreciated!)
The picture shown in this Intro page is the fully assembled and mounted on top of the interior mirror of my car showing the bearing, angle and current interior temperature. Unfortunately I didn't take a lot of pictures when I assembled the electronic parts, but I'm sure someone who are interested in making one of these will be able to follow easily the schematic diagram I will show in a couple of steps later.