Simple Touch Switch using transistors

Video Tutorial

This circuit turns on LED with the touch of your finger!. Many a times we need certain actions to be done with a touch instead of pressing a button. This simple circuit does that using minimal components. Step by step instructions on how to build the circuit are in the video below. Also, this circuit can be coupled with a latch and relay to control electronic appliances with a touch. So start experimenting building different variants of this project.

Working:

The purpose of this project is to trigger/switch an LED with a simple touch. The skins resistance is about 600K-1M. So if you try building a circuit with just an LED, power supply and touch conductors, the LED doesn't glow. This is because, high skin's resistance prevents enough current to flow through the circuit. So the only option we have is to amplify the tiny current flowing through the skin to a magnitude enough for an LED to glow. For that purpose, we have to use transistors. The circuit will also work with just one transistor, but the LED doesn't glow bright enough. So we have used two.

Tiny electric current flows through the skin when the end touch conductors are touched. This tiny current is amplified in magnitude by the first and second transistors and it finally passes through the LED. Refer to the circuit diagram for better understanding.

Components Required:

  • 2 BC547 (or any other npn transistors)
  • Resistors: 270 Ohm, 100 KOhm
  • LED
  • Breadboard Connectors
  • Breadboard
  • 6V Power Supply

Circuit Diagram:

Touch Switch Circuit Using Transistors - Schematic