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 2x16LCD. 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.