Schematic Reference

This 9-minute timer switch can be used to control the light in a toilet or bathroom. The timer is started by pushing S1 and stopped by pushing S1 again. If you forget to turn it off, the controlled light will go off after nine minutes. If you need the light on continuously non-stop, you need to press S1 (turn on) and then S2 (cancellation of timer) within 9 minutes and in this case the light will be on until you switch it off with S1.

IC1 is a is 4013 dual flip-flop. Flip flop IC1a is toggled on and off by switch S1 and it controls the relay which is switched by FET Q2. IC1a controls IC1b which is connected as an RS flipflop to enable or disable IC2, a 4060 oscillator/divider. This has its timing interval set by the components at its pins 9, 10 & 11. The relay should have 250VAC mains-rated contacts and these are connected in parallel with an existing wall switch.

Author: Rasim Kucalovic - Copyright: Silicon Chip Electronics