If you want to build some interesting clock, perhaps you can try this, Propeller Clock. In this project, scanning Led process uses spin motor. It will give Illusion of numbers in the air.
How this clock works:
A motor spins the “propeller”, and a small microcontroller keeps track of time and changes the pattern on seven LEDs with exact timing to simulate a 7 by 30 array of LEDs. It is an illusion, but it works nicely.
If you want to build this clock, you will need a few things, including:
1. Skill with motors and mechanical things.
2. Prior electronic experience.
3. A dead VCR or floppy drive or other source of a suitable motor and miscellaneous parts.
4. A programmer that will program a PIC16C84 or 16F84 or AVR microcontroller.