Light/Dark Detector Project
Create an automatic night light that turns on in the dark and off when there's light.
Required Components
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- LDR (Light Dependent Resistor)x1
- Transistor (BC547)x1
- Potentiometer (10kΩ)x1
- LED (any color)x1
- Resistor (330Ω)x1
- 9V Battery & Connectorx1
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Components Required
- LDR (Light Dependent Resistor)x1
- Transistor (BC547)x1
- Potentiometer (10kΩ)x1
- LED (any color)x1
- Resistor (330Ω)x1
- 9V Battery & Connectorx1
Instructions (Dark Detector)
This circuit acts as an automatic night light. The key component is the LDR, whose resistance changes with light intensity. We use this change to control a transistor that acts as a switch for the LED.
- Understand the Voltage Divider: The 10kΩ potentiometer and the LDR create an adjustable voltage divider. This allows you to fine-tune the light level at which the circuit activates.
- Assemble the Circuit:
- Connect one outer terminal of the 10kΩ potentiometer to the +9V supply.
- Connect the other outer terminal of the potentiometer to one lead of the LDR.
- Connect the other lead of the LDR to Ground (GND).
- Connect the center terminal (the wiper) of the potentiometer to the base of the BC547 transistor (Q1).
- Connect the emitter of the transistor to Ground.
- Connect the collector of the transistor to the 330Ω resistor (R1).
- Connect the other end of the resistor to the cathode (shorter lead) of the LED.
- Connect the anode (longer lead) of the LED to the +9V supply.
- Calibrate and Test: Power the circuit. By turning the potentiometer's knob, you adjust the voltage sent to the transistor's base. Find a position where the LED turns on when you cover the LDR and turns off when it's exposed to light.
To build a Light Detector (LED on in light): Simply swap the positions of the LDR and the potentiometer in the circuit.
About This Project
This project is a perfect introduction to sensors and analog electronics. By building it, you'll learn how voltage dividers work and how transistors can be used to amplify a small signal to control a larger load.