Touch Switch Using NPN Transistor BC547 Full Making Project

Circuit Description:

1. NPN Transistor (BC547):
   • The NPN transistor is used as a switch. When the touch-sensitive plate is touched, it changes the biasing of the transistor.
2. Resistor (R1):
   • R1 is connected between the positive voltage rail and the base of the NPN transistor. It is used for biasing the transistor.
3. Touch-sensitive Plate:
   • The touch-sensitive plate can be any conductive material. When touched, it introduces a capacitance change that affects the biasing of the transistor.
4. LED:
   • The LED is connected to the collector of the NPN transistor. When the touch-sensitive plate is touched, the transistor turns on, allowing current to flow through the LED.

How It Works:

1. When the touch-sensitive plate is not touched, the transistor is in an off state, and the LED is off.
2. When the touch-sensitive plate is touched, it introduces a capacitance change, affecting the biasing of the transistor.
3. The changed biasing allows current to flow from the collector to the emitter of the NPN transistor.
4. The activated transistor powers the LED connected to its collector, causing it to light up.
5. When the touch is released, the transistor returns to the off state, turning off the LED.