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# Light sensor (on when dark)

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turns ON the light when it gets dark around

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• You can find the circuit diagram here: http://circuitdigest.com/electronic-circuits/darkness-detector

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• where is circuit diagram???

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### Light sensor (on when dark)

1. 1. Light Sensor Night SwitchingEquipment List Equipment name Quantity used in a circuit Quantity used in Whole Project Transistor (npn) 2 60 LEDs (White) 2 60 Variable Resistor 1 30 Resistance (10K) 1 30 Resistance (1K) 1 30 LDR 1 30Specifications Equipment No. Voltage Resistance Power Current name Transistor C 1383 LED 3V 15 (mA)Variable resistor 0-20 K 0.25 W Resistance 10 K 0.25 W Resistance 1K 0.25 W LDR 4 K -20 k 0.25 W
2. 2. Calculations
3. 3. Circuit Diagram
4. 4. Theory/ Basic Principle We have to make the Light Sensor Night Switching. We used two Transistor one LDR, onevariable resistance,10 k resistance,1 K resistance two LEDs and Input Source of 9 V .weconnected a resistance of 1k in Series with Base of transistor (T1) and also Connected theother components of the circuit as shown in the circuit diagram. We Used the commonEmitter Configuration of the transistor in this circuit. If we used only one transistor than the circuit will be day light switching we have to makethe night switching so we inverted the output by connecting the base of other Transistorwith the collector of first transistor.Transistor (T1) is ON when light is falling on the LDR because the voltage drop across thevariable resistor is greater than 0.6 volt so that’s why the Emitter Collector is Shorted allcurrent passes through this and Transistor (T2) is turned OFF we are getting the outputacross T2 so when light is falling we got no output when light is not falling than T1 is OFFand T2 is ON so as we got the output in dark. we connected the LEDs to check the output.This the basic principle of our project.This the concept of single circuit in our project. we connected 30 such circuit in the projectand controlled these individually.We make the circuit such sensitive that it can response to the shadow of your figure in notime.Result The result of our project is that it turned ON in the dark and turned OFF when light is fallingon it. We have shown the output by glowing LEDs.This is the circuit that Engr.Sohail Afzal Assign us. Comments