This is a project of a simple toggle switch circuit using a CD4017 IC. With this circuit any AC or DC electronic device can be operated with a single push button. The circuit can also be used in variety of electronic projects to activate or deactivate the relay switch on single pulse.
The IC used in the circuit is a very famous CMOS decade counter or divided by 10 counter IC of 4000 series manufactured in 16 pin DIP package with many good built in features like supply voltage 3V to 15V DC, low current consumption, fully static operation etc. The IC can be used in wide variety of applications from educational and home to industrial purposes.
The clock input pin 14 controls all the 10 outputs of the IC and activate each output on a single positive pulse. In most circuits this work is done by a multivibrator circuit but in this project this IC is used as a simple toggle switch so the pin 13 is connected to the ground to freely run the IC and the pin 15 is connected with the 2nd output of the IC that is pin 4 to toggle the IC between the output 1 (pin 2) and 0 (pin 3) by pressing the push switch. On the output 0 or pin 3 we have connected an LED with a current limiting resistor, when this LED is activated it will indicate that the output at pin 3 is high or the output of pin 2 is low and the relay is not activated. Now in the opposite situation when the output at the pin 2 goes high it will activate the relay through the 2N4401 transistor, and the output at pin 3 goes low and the LED1 becomes deactivated. The output of the CD4017 is not enough to operate the relay directly due to which we have used a transistor to drive the relay.
Another LED (LED 2) is also connected with a current limiting resistor between the transistor's collector and positive supply to indicate the activation of the relay.