The OBD2 connector all current cars offer interesting information about the current state of electronics such as speed, turbo pressure, temperature and sensor mount almost any manufacturer. Based on this, Pete Mills has made a nice little Digital tachometer ring made with RGB LEDs WS2812. Keep in mind that the OBD protocol can become a real hell since each manufacturer adds his brushstrokes. Besides that, according to the continent from which proceed the vehicle, the OBD-II protocol is different (USA) and EOBD JOBD for Europe to Japan. Pete has helped Ford API OpenXC and its website has all the details.