This project based on Arduino, it will measure time of one revolution of wheel, then divide wheel's lenght on this time, and it will be the speed. Revolutions of wheel will be measured by magnet and hall sensor. I used servo motor with arrow and scale to show the speed, it looks like "analog". Also I used 7 segment display to show distance (odometer), also arduino write odo in its EEPROM after bicycle is stopped, so odo keeps in Arduino and not clears after system reboot.
You can watch all process of making this device IN THIS VIDEO