Saturday, November 15, 2014
LIGHT DETECTOR CIRCUIT
Light detectors are one of the most popular sensor and they are commonly found in many real-world applications. They are widely used by electronic hobbyists and projects because they are practical and intriguing yet surprising easy to construct. This will guide and show you how easy it is to make your own light activated Light Emitting Diode (LED) with minimal tools and materials. The whole project is simple. This implementation can be used for an educational demo or applied directly to the practical world.
Parts
- Breadboard or PCB Board
- A few Jumper Wires
- 9 Volts Battery
- 9 Volts Battery Clip
- Light Dependent Resistor (LDR)
- Light Emitting Diode (LED) with any color of choice
- TLC3704 Quad Comparator (only one of its four comparators will be used) (Alternatively, you can use the single LM311N Comparator with 8pin)
- 3362P-103-ND 10K Ohms Variable Resistor
- 1K Ohms (Brown-Black-Red) Resistor X2
- 330 Ohms (Orange-Orange-Brown) Resistor
Circuit Diagram
Working
As its name suggests, a comparator compares two given voltages. The pair of 1K ohms resistors create a voltage divider and provide a 4.5 volts reference for the comparator. The variable resistor and LDR both form another pair for a second voltage divider. When light falls on the LDR, its resistance lowers and that voltage divider provides a voltage lower than 4.5 volts. The comparator produces no output (0 volts). When light is absent, the resistance of the LDR and the voltage increases. When the voltage increases over 4.5, the comparator activates its output and supplies 9 volts to power the LED.
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