LED On/Off with Light Dependent Resistor (LDR) and NPN Transistor

 LED On/Off with Light Dependent Resistor (LDR)

Components Required :

1. Printed Circuit Board (PCB)
2. LED
3. 10kohm Resistor
4. 1Kohm Resistor
5. NPN Transistor
6. Light Dependent Resistor (LDR)
7. Battery Holder
8. Solder Gun
9. 9V Battery

Connections:

1. Connect the NPN transistor to the breadboard as shown in the image.
2. Connect the base of the NPN transistor to one terminal of the Light Dependent Resistor (LDR) and another terminal of the LDR should be connected to the emitter of the NPN transistor, which would be further connected by the negative terminal of the battery.
3. Connect one terminal of the 10Kohm resistor to the base of the NPN transistor.
4. Further, connect one terminal of the 1Kohm resistor to the positive terminal of the LED.
5. Another terminal of the 1Kohm resistor should be connected to the second terminal of the 10Kohm resistor.
6. Lastly, connect the negative terminal of the battery to the second terminal of the LDR and the positive terminal of the battery should be connected to the remaining terminals of the 10Kohm, and the 1Kohm resistors.

Circuit Design:

Working Principle:

• When light falls on the Light Dependent Resistor (LDR), the LED turns off.
• This circuit works on the principle of photoconductivity.

LED ON

LED OFF

Similar circuit is performed on paper using copper tape and PCB (Printed Circuit Board) by soldering.

PAPER CIRCUIT