This is a countdown counter based on ATtiny2313, primary developed for my PCB exposure box, but it can be used for other purposes too.
The counting range is between 1 and 90 minutes and it can be adjusted with up or down buttons (high and low in the pictures).
After the desired time is set, the countdown starts by pressing the start/stop button (on/off in the pictures). By pressing the same button we can interrupt the counting at any time we want.
After the count expires we hear a beeping sound and the load is disconnected. By pressing start/stop button we reset the counter and we are ready for another lap. All actions included the time remaining are shown in the LCD display.
Pcb countdown timer - [Link]