If you need simple, reliable countdown timer for PCB exposure or even in the kitchen - this project is what you may need.

Circuit of this timer is very simple – AVR Attiny2313 microcontroller gets commands from three buttons (Time Up, Time down and Start), displays it on 2×16LCD. You can connect any device to be controlled to relay. After timer counting is over – it gives a sound signal via buzzer. Project schematic and PCB is developed with Eagle CAD software. Firmware is written in Basic language with Bascom. Time to cook.