Binary clock - Easy to build
A binary clock for Arduino Uno
Everything you need to know is in the 2 files, but here the parts anyways:
1 Arduino Uno
4 leds of any color
6 leds of any other color
1 led of a third color
11 220Ω resistors
12 wires, I recommend 1 black/blue and 11 red
The clock isn't accuarate enough to run for a long time, but it's a cool anyways ;) have fun