LDR-Based Automatic LED Circuit Design:
How This Circuit Works
This circuit is a Light-Dependent Resistor (LDR) based automatic LED control circuit that turns on the LED when the surrounding light intensity decreases. It operates as follows:
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LDR Functionality: The Light Dependent Resistor (LDR) has a resistance that varies with light intensity:
- In bright light, its resistance is low (a few hundred ohms).
- In darkness, its resistance is high (several kilo-ohms to mega-ohms).
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Voltage Divider Network:
- The LDR and 47KΩ resistor form a voltage divider.
- The voltage at the junction of the LDR and 47KΩ resistor controls the base of the BC547 transistor.
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Transistor Operation:
- When light is present, the LDR resistance is low, so the voltage at the transistor’s base is low, keeping it in the OFF state.
- When darkness occurs, the LDR resistance increases, raising the voltage at the transistor’s base, turning it ON.
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LED Activation:
- When the transistor turns ON, current flows through the 1KΩ resistor and LED, causing the LED to glow.
Why This Circuit Is Designed?
This circuit is designed to automatically turn on a light (LED) when the surrounding becomes dark, eliminating the need for manual switching. It is a simple yet effective light-sensitive switch.
Where This Circuit Is Used?
This circuit is widely used in various light-sensitive applications, such as:
- Automatic Street Lights – Turns on streetlights at night and off during the day.
- Home Automation – Can be integrated into home lighting systems.
- Garden or Decorative Lights – Activates outdoor lights automatically at dusk.
- Security Systems – Can be used in alarms or safety indicators.
- Solar Lighting Systems – Helps in controlling solar-powered LED lights.
This circuit is an excellent project for beginners learning about LDRs, transistors, and automation in electronics.
You can visit my circuit in DCAClab is related this.
Thanks
Md. Anisur Rahman