Touch switch using BC547 transistor

Touch switch using BC547 transistor 

AIM

To construct a circuit that will activate by touching of human hand by using BC547 transistors.

Components required

Sl no	Component	Specification	Quantity
1	Transistor	BC547	2
2	LED	Any color	1
3	Resistor	220 Ω	1
4	Resistor	1 KΩ	1
5	Buzzer		1
6	Power supply	9v	1

Theory

In this project, we will learn how to build a simple touch switch using a single transistor. When someone touches the two endpoints in the circuit, the LED in the circuit lights up and it turns off when the finger is removed. This circuit can be used to teach students about human body electrical resistance and the basic current amplifying property of a transistor. 

BC547

BC547 is a bi-polar general purpose NPN transistor that is commonly used in switching and amplifying applications. It can found in relay driver, LED driver and other medium power switching devices and audio or signal amplifiers. The pin configuration of BC547 is:- 

Circuit diagram

Working principle

When we touch the base lead and the 1KΩ resistor in the circuit, very small current flows through the circuit. This current is determined by the electrical resistance of your body and the 1KΩ resistor. For practical purposes, we can ignore the base to emitter resistance of the transistor. The human body resistance usually is in the order of around 100KΩ.

One of the basic properties of a transistor is its current amplification property. A small current through the base to emitter allows a much higher current from collector to emitter. This multiplier is known as the gain of the transistor.

Watch video

https://youtu.be/FJ3Iz8Xy_qc