Programmable timers are used in many areas. You can set timer to turn on/off light after some time, turn off oven, control water sprinkler and do other time dependent switching. You can buy such timer for cheap – some of them even plugs in directly to AC outlet. But if you like to have things in control and be able to add additional features, then you can build a simple timer with small microcontroller. Hristo has built a programmable timer on PIC16F628A microcontroller. He intended this timer to be used in hos UV light exposure box. But by adding a relay, it can be used for anything.
Timer can be set and run with three switches where couple of them are for setting minutes and seconds. LCD indicates timer running state and is used to navigate menu while setting time. Timer also has a calibration jumper where timer can be adjusted to run more accurate. Once timer runs out timer turns switch off and then sounds buzzer alarm. Really simple and useful circuit.