Speedometer is tested on Arduino Uno with AtMega328 chip.
the SevSeg lib https://docs.google.com/file/d/0Bwrp4uluZCpNdE9oWTY0M3BncTA/edit
I used old bike speedometer reed switch, but you can use a hall effect sensor or brand new reed switch for wheel movement tracking.
info: http://en.wikipedia.org/wiki/Reed_switch http://en.wikipedia.org/wiki/Hall_effect_sensor http://playground.arduino.cc/Main/SevenSegmentLibrary
wiki of this project:
https://github.com/PavelasV/2DigitsSpeedometer/wiki
-more info will be soon available