LED revolution counter with EL backlight. A small video can be seen at http://www.youtube.com/watch?v=JJKnmF2y7Ns.
It consists of the ATARI controller, a display with KS0108-compatible controller a small microcontroller board with ATMEGA1284P. A video can be seen at http://www.youtube.com/watch?v=4JVwS3N1E14.
My last car (Seat Ibiza, 2008 model) had a mount for a TomTom satnav. Wanting to use my Samsung Galaxy S3 for navigation, I bought a SGS3 car mount and converted the TomTom mount to carry the S3.