The LDR. LDRs (light-dependent resistors) are used to detect light levels, eg in automatic security lights. Their resistance decreases as the light intensity increases. In the dark and at low light levels, the resistance of an LDR is high, and little current can flow through it. High sensitivity (due to the large area it can cover). Easy employment. Low cost. There is no union potential.
Using an LDR and a few components, this is a very basic circuit for turning on a light in the dark. The sensor is an LDR, and the electronic switch is a transistor.
The resistance of the LDR changes when light falls on its surface. The less light there is, the less resistance there is. A potential divider circuit is created by connecting resistance R1 (100K) and LDR in series. The intensity of the light affects the divided voltage. Because the LDR is linked to the Ground, the voltage loss increases as the light intensity rises. It is sensitive to a wide range of light.
An NPN Transistor BC147/BC548 is fed from the Potential Divider’s center point. As the base voltage of this general purpose NPN silicon transistor is around 0.5V or higher when compared to the emitter voltage, the circuit is completed, and the LED illuminates in the dark.
- Resistance of 100K
- BC548 is a transistor.
This Magic Eye circuit is both inexpensive and simple to construct. It will only cost you about 20 cents (Rs 15).
Automatic street lights, Electronic Letter Boxes, Electronic Eyes, Automatic Vehicle Headlights, and Automatic Garden Lights may all be made with this LDR circuit.