This project is based around a PIC micro-controller. The time is set by the rotary switch to one of 12 different settings ranging from 1 to 20 minutes. As soon as the start button is presed the timer begins counting down with the minutes remaining displayed in the dual 7-segment display. When the time is up the unit beeps for 7 seconds. After a while the unit then powers down to sleep mode until the start button is pressed to save battery power. The battery used is a 9v PP3.

The timing intervals on the switch are: 1, 2, 3, 4, 6, 8, 10, 12, 14, 16, 18 and 20 minutes. These can be changes in the program.doc file in the Time variable table. If you want a pre-programmed PIC with different time intervals please specify them when you order.

Download Circuit details and PCB, (PDF - 72K).

The PCB holds all the components except the start and power switch. Care must be taken when fitting the rotary switch that it is correctly orientated and the switch connections shaped so they will fit through the PCB. Also ensure the PCB holes for the switch are drilled to at least 2mm.

The PCB needs to be secured to the front of the case. The mounting of the rotary switch holds the PCB to a certain extent, but the thread is only plastic and will not take too much strain. Try to add some other form of fixing if possible.