Hi, Guys in this tutorial we will learn, how to make an electronic circuit that will detect the light. That means if the light is there then the Led will turn on otherwise it will be turned off. So this is basically for the school student's project for their Science Exhibition.

Parts Required:

  1. LDR
  2. 5k Potentio Meter
  3. 220 Ohm Resistor
  4. Single Strand Wire


How to make ??

Before Building the project lets have a look at BC547, it has 3 pins Emitter, Base Collector.

A transistor is basically an electrically controlled switch. There is an input, output, and a control line referred to as the emitter, collector, and base. When the control line (base) is triggered it will connect the emitter and the collector just like switching a switch. Since the power between the emitter and collector can be higher than the base, transistors are often used as amplifiers.

The BC547 is an NPN transistor meaning when power is applied to the base (control pin) it will flow from the collector to the emitter. Typically NPN transistors are used to “switch ground” on a device, meaning, they are placed after the load in a circuit.

Let's Build it

1. Connect the pin 1 [Collector] of BC547 to the ground pin of the led.

2. Now Connect one 220 ohm resistor to the +ve pin of the red led.

3. Now connect the LDR as shown in the diagram below.

4. Now connect the 5k potentiometer to the pin 3 of the BC547 and to the point where 220ohm resister and one end of LDR is connected.

5. Now connect the Pin 3 of the BC 547 to the 9v power supply ground pin, and 9v power supply +ve pin to the point where one end of 220ohm resistor, one end of LDR is connected. As shown in the Diagram Bellow


Now when you will make the surrounding Dark you will observe that LED will stop glowing and when you will allow the light to come then the LED will glow again. So here LDR acts like a Switch.

For making Please Watch this video: