This Toggle Switch uses the popular Johnson Decade counter IC CD4017. By giving positive pulses to its clock input, the ten outputs of the IC becomes high one by one provided the reset pin is grounded. By connecting the reset pin to any of the output, IC latches and the output remains high irrespective of the clock pulses. This toggle action can be exploited in various relay driver circuits.
In the circuit IC CD 4017 is used in the Toggle mode. Its clock inhibit pin is grounded so that IC can run freely. But the reset pin is shorted with the Q3 output (Pin 7) so that IC will toggle between Q1 and Q2 outputs. When the clock input pin 14 receives a positive pulse, first output Q1 goes high as indicated by the Red LED. This is the OFF Mode.
By another pulse, the second output Q3 becomes high and Q1 turns off. This is the ON Mode. When the Q2 output becomes high ,T1 conducts and relay turns on. Relay can be switched off by another pulse in the clock input. Positive pulses can be given through astable or monostable circuits.