Introduction:
The LDR-based dark detector is a simple and efficient circuit that uses a light-dependent resistor (LDR) and the NE555 timer IC to detect changes in light intensity. The LDR's resistance decreases in light and increases in darkness. This variation controls the input to the NE555, which acts as a comparator. When the environment is dark, the circuit outputs a high signal, turning on an LED as an indicator. Conversely, in light, the LED turns off. Widely used in automatic night lamps and light-sensitive systems, this circuit is cost-effective, easy to build, and ideal for beginners exploring electronics projects.
Component Required:
NE555 Pinout:
Circuit Diagram:
Working Explaination:
This LDR-based dark detector circuit uses the NE555 timer IC as a comparator to detect low light levels. The LDR and a 4.7 kΩ resistor form a voltage divider, providing a variable input to pin 2 (trigger) of the NE555. In darkness, the LDR's resistance increases, raising the voltage at pin 2. When this voltage drops below 1/3 of the supply voltage (due to light), the NE555 output (pin 3) goes low, turning the LED off. Conversely, in darkness, the output goes high, powering the LED through a 1 kΩ resistor. A 47 kΩ resistor and capacitors stabilize the circuit, while a 100 µF capacitor smooths the LED's operation. This circuit is ideal for light-sensitive applications.
Applications:
- Automatic Night Lamp
- Streetlights Automation
- Security Systems
- Light-Sensitive Alarms