With this circuit you can control any of your electrical appliances from any point with only two wires extending from the circuit to those points. One need not, for instance, keep the passage lights on always since the accessibility of the switch can be provided to every require point. It can thus be used in energy saving device in long passages.
In this circuit, switches SW1, SW2, SW3….SWn are connected between the clock pin of IC CD4042A and the power supply. The Q output pin 3 of the FF is feedback to its D input pin 4. The output from pin 2 is connected to the base of darlington pair amplifier formed by BC107 and SL100, which drives the relay. The connection to the appliance can be through the N/O contact of the relay. The circuit is powered by 12V DC. The impedance of the relay used should be greater than 100-ohm.
With this circuit you can easily make a three way switch or switch with unlimited numbers of terminals where each can individually control the output.
There is no need to connect a debouncing circuit between the switches and the IC.
Resistors (all ¼-watt, ± 5% Carbon)
R1 = 10 KΩ
R2 = 3.3 KΩ
R3 = 1 KΩ
R4 = 10 Ω
C1 = 50 µF/25V
IC1 = CD4042A
T1 = BC107
T2 = SL100
SW 1 – SWn = Push to on switch
RL1 = 12V, >100 Ω relay