I needed a sempahore and decied to create a simple one with an old PCB. 

It uses an ATMEGA168 as a microcontroller.

5v--- BTN-----> PIN4 (INT0)
        |
        150R
        |
        GND
        
 GND---150R---|<RED     ----> PIN11 (PD6)
 GND---150R---|<YELLOW  ----> PIN12 (PD7)
 GND---150R---|<GREEN   ----> PIN17 (PB0)