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

Automated street light switching project

Automated street light switching project 

AIM

To construct a circuit that will switch on the street light automatically during dark and will off during day time by using BC547 transistors and LDR.

Components required

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

Theory

LDR

LDR stands for light-dependent resistor is an active component that decreases resistance with respect to receiving luminosity (light) on the component's sensitive surface. The resistance of a LDR decreases with increase in incident light intensity and vice versa.

 In the dark, a LDR can have a resistance as high as several mega ohms (MΩ), while in the light, a LDR can have a resistance as low as a few hundred ohms.

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 

The working principle of LDR is that it gives less resistance in high light intensity and high resistance in low light intensity (ie) it gives high resistance in dark or night and low resistance in day or light.

Here we use transistor as a two way switch. If the voltage through base is greater than 5V it send through the emitter. If the voltage through base is less than 5V the it sends through collector.

During night the LDR gives a high resistance as a result the voltage passing through the base will become less than 5V so the LED glows.

During day time LDR gives a low resistance as a result the voltage through base is greater than 5V which switches the current to the emitter. This turns LED off.

Watch video

https://youtu.be/TCkyn5rLxWk