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