Touch Switch Circuit Using Timer IC 555

In this simple Touch Switch circuit we have used timer IC 555 operated as ON and OFF.  By using this circuit you can turn ON and OFF a device by simply touching the Touch Plates or metal used as sensor. If the touch plates are placed at a convenient place, we do not require to move from our location to turn on and off the device. The important feature of this circuit is that we will not get any electrical shock which we sometimes get while using the normal switches.

Components Required

  • 555 Timer IC
  • 3.3 MΩ Resistor (1/4 Watt)
  • 1 MΩ Resistor (1/4 Watt)
  • 1 KΩ Resistor (1/4 Watt)
  • Bulb with holder (regular or CFL)
  • 5V Relay
  • BC547 NPN Transistor
  • 1N4007 PN Junction Diode

Circuit Diagram

Touch switch circuit

Circuit Design

Design of the Touch ON and Touch OFF Switch circuit is very very simple. We have connected the pin no 8 and 4 of the 555 with VCC supply and pin 1 is connected to GND and 5V respectively. Pin 2 of IC is pulled HIGH using a 3.3 MΩ Resistor and Pin 6 is pulled LOW using a 1 MΩ Resistor.

As shown in the diagram two touch plates are connected. In case of the touch to ON plate, one end is connected to pin 2 and other end is connected to – supply. Similarly, one end of the touch to OFF plate is connected to VCC (5v) and the other end is connected to Pin 6.

Working of the Project

  • After Connecting the circuit as per the circuit diagram and apply the 5v power supply.
  • Touch the “ON” plate with your finger and to turn OFF the device , touch the OFF plate as shown in the circuit diagram.
  • As power supply is applied to circuit, the device connected through the relay (we have connected AC bulb) remains OFF. Now if we observe the circuit diagram, Pin 2 of 555 IC is pulled HIGH and Pin 6 is Pulled LOW.
  • As we touch the ON plate, voltage at Pin 2  of the 555 IC becomes LOW. As Pin 6 is already LOW, the output at Pin 3 becomes HIGH.
  • This is connected to the Relay through the Transistor BC 547, the Transistor will be turned ON and it will activate the Relay and device gets switched ON.
  • At this point voltage at pin 6 of 555 ic is zero as it pulled LOW by default and voltage at Pin 2 of IC is HIGH.
  • Now, as we touch the OFF plate, Pin 6 is supplied with + supply for a brief time and as a result, the output of  IC will become LOW.
  • This will turn off the transistor and deactivate the relay. AS result, the device will be switched OFF.

Applications

  • A simple Touch to ON and Touch to OFF Switch Circuit can be used to control simple LED without using any relay.
  • If we want to control the AC appliances then we have to use relay with this circuit.
  • Any AC appliance can be controlled by suing this circuit

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  1. Nice Article

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