Using circuit diagram below can be built a simple timer for lamp, or other electronic device.
Pressing S1 determine tipping IC1b flip-flop and generates a clock pulse vibration-free on entry of the second flip-flop, IC1a, whose output goes to "1", activating low power thyristor, Th1. Exit complementary flip-flop, Q, go to "0" and validates the timer IC2. Low power load (max. 60 W), is powered and remains connected until the counter will reset flip-flop IC2 IC1a.
Counter, type CD4541, includes an oscillator working at a frequency f, given in Hz:
f = 1 / 2.3 CTC RTC where the RTC and CTC are resistor and capacitor connected to pinul1 or 2. Resistor connected to the input RS pin 3 has a value of about 2 RTC.
Delay, t, in seconds, can be calculated by the formula:
t = 2.3 x 32,768 x R5 x C5.
The circuit is powered directly from the mains. Transistor T1 forms a zener diode of 10 V.