Automatic Street Light Control using LDR and Transistor BC 547
1. Project Description
This project presents an automatic street light system that intelligently turns on at night and off during daylight. It eliminates the need for manual operation by using a simple electronic circuit. The core of the system relies on a Light Dependent Resistor (LDR) to sense ambient light levels and a transistor to switch the street light (LED) on or off accordingly, ensuring energy efficiency.
2. Objective
The key objectives of this project are:
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To design a cost-effective and reliable automatic street lighting system.
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To significantly reduce energy consumption by preventing unnecessary usage.
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To eliminate manual intervention, enabling fully automated operation.
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To demonstrate the practical application of basic electronic components in solving a real-world problem.
3. Components
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LDR (Light Dependent Resistor): Acts as the sensor whose resistance changes with light intensity.
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Transistor (BC 547): Functions as an electronic switch to control the LED.
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Resistors (e.g., 1kΩ, 330Ω): Limit current and set the bias voltage for the transistor.
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LED: Simulates the street light in this prototype.
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Battery (6V or 9V): Provides the DC power supply for the circuit.
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Breadboard & Connecting Wires: For assembling and connecting the circuit.
4. Working Principle
1. Sensing and Switching Mechanism:
The LDR's resistance is high in darkness and low in bright light. This change in resistance alters the voltage at the base of the transistor BC 547. When it's dark, the LDR's high resistance allows sufficient voltage to reach the transistor's base, turning it ON. This completes the circuit for the LED, causing it to glow.
2. Component Interaction
The LDR and a fixed resistor form a potential divider network connected to the transistor's base. The transistor acts as a switch whose state (ON/OFF) is controlled by this base voltage. The collector of the transistor is connected in series with the LED and a current-limiting resistor. Thus, the transistor's switching action directly controls the power flow to the LED.
Circuit Diagram
Circuit Diagram of the Automatic Street Light Control System.
5. Hardware & Results
The hardware consists of the components listed above, assembled on a breadboard as per the circuit diagram. The result is a fully functional prototype that automatically illuminates the LED when the surrounding light level drops below a certain threshold (simulating night). Conversely, the LED turns off when sufficient light is detected, successfully demonstrating automatic control.
Implemented Hardware Prototype on a Breadboard
6. Applications
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Public street lighting systems.
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Garden and park pathway lights.
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Parking lot and area illumination.
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Outdoor security and perimeter lighting.
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Residential porch and backyard lighting.
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Highway and tunnel lighting automation.
7. Conclusion
The "Automatic Street Light Control" project was successfully designed and implemented using an LDR and a BC 547 transistor. The circuit efficiently automates the switching process based on ambient light intensity. This project confirms that a simple, low-cost electronic system can effectively solve a real-world problem, paving the way for smarter and more energy-efficient urban infrastructure.