This article is about a Simple Transistor Based Touch Switch Circuit, it works when finger touches the pad with no push button used; human body gives small signal and circuit senses this signal.
The circuit uses two NPN transistors and an LED as the output, also it operates with only a 3V supply, making it a very simple circuit for beginners.
Circuit Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistors | 1k, 220Ω 1/4 watts | 1 each |
| Semiconductors | Transistor BC547 NPN | 2 |
| LED any color | 1 | |
| Power Supply 3V Pencil cell | 1 | |
| Touch Pad Metal wire, plate or copper | 1 |
In the above circuit diagram when human finger touches the touch pad the small current flows and this current goes to base of Q2 transistor and this Q2 transistor turns ON.
Then collector voltage of Q2 changes and its voltage goes to base of Q1 and Q1 transistor turns ON with current flows through LED and resistor.
The LED now glows and when we remove our finger, the signal stops, both transistors turn OFF and the LED also turns OFF.
How to Build:
To build a Simple Transistor Based Touch Switch Circuit follow the below steps for connection:
- First, assemble all components as per circuit diagram.
- Next, Q1 transistor emitter connect to battery negative, Q1 collector connect to LED cathode and LED anode connect to battery positive through resistor R2.
- Then Q1 base connect to collector of Q2.
- After that, Q2 transistor emitter connect to base of Q1, Q2 collector connect to one side of resistor R1 and other side of R1 connect to battery positive
- Then Q2 base connect to touch pad.
Conclusion:
To conclude, this Simple Transistor Based Touch Switch Circuit is easy to build and useful because it uses basic electronic components and requires only a low-voltage supply.
Moreover, its a good project for students and beginners which helps to understand transistor working.