This article is about is 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.
Two NPN transistors are used and one LED is used as output.
Circuit works with only 3V supply which is very easy circuit for beginners.
Circuit Working:
Parts List:
| Components | Value | 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.
This current goes to base of Q2 transistor and this Q2 transistor turns ON.
Collector voltage of Q2 changes and its voltage goes to base of Q1.
Q1 transistor turns ON with current flows through LED and resistor.
LED glows, when finger is removed and signal stops.
Both transistors turn OFF and LED also turns OFF.
How to Build:
To build a Simple Transistor Based Touch Switch Circuit follow the below steps for connection:
- Assemble all components as per circuit diagram.
- Q1 transistor emitter connect to battery negative.
- Q1 collector connect to LED cathode.
- LED anode connect to battery positive through resistor R2.
- Q1 base connect to collector of Q2.
- Q2 transistor emitter connect to base of Q1.
- Q2 collector connect to one side of resistor R1.
- Other side of R1 connect to battery positive.
- Q2 base connect to touch pad.
Conclusion:
This Simple Transistor Based Touch Switch Circuit is easy and useful.
It uses basic electronic parts with only low voltage supply is needed.
Its a good project for students and beginners which helps to understand transistor working.