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Hey there!, in this project i will see how to use LDR to make a darkness sensor circuit on breadboard.
basically, this circuit turn on a light in darkness and turn off light in brightness.
Component required:
LDR
50k ohm & 1k ohm resistor,
BC547 transistor,
9v battery
Circuit Diagram:
What is LDR ? :
LDR is a photoresistor is a light-controlled variable resistor. The resistance of photoresistor decreases with increasing incident light intensity,in other words, it exhibits photoconductivity.
A photoresistor can be applied in light-sensitive detector circuits,
and light- and dark-activated switching circuits.
BC547 TRANSISTOR : BC547 is an NPN bipolar junction transistor. A transistor, stands for transfer of resistance,is commonly used to amplify current.
A small current at its base controls a larger current at collector & emitter terminals.BC547 is mainly used for amplification and switching purposes.
It has a maximum current gain of 800. Its equivalent transistors are BC548 and BC549.
Here, i attached datasheet
Procedure :
Follow diagram for complete connection of circuit.
50K ohm resistor one end is connected with Positive (9V) of battery and other end is connected in series with LDR and LDR another point is connected with negative of battery.
I have used 2 100K ohm resistor in parallel because i do not have 50K one.
1K OHM resistor one end is connected with Positive (9V) of battery and other end is connected with anode (positive) of LED. Cathode (negative) of LED is Connected with C (collectr) of BC547 Transistor.
Emitter (E) of transistor is connected with the negative of battery
Base (B) is connected Junction point of the 50K resistor & LDR
It is a simple and powerful concept , which uses transistor ( BC547 NPN) as a switch to switch ON and OFF the LED LIGHT automatically .
It automatically switches ON lights when the light goes below the visible region of our eyes.( e.g in evening after Sunset ). it automatically switches OFF lights when light fall on it ( e.g in morning ) , By using a sensor called LDR (Light Dependent Resistor) which senses the light just like our eyes.
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