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Light detector using LDR
The LED turns ON when light is incident on the LDR . This project is widely used in security systems .
Akshay SrivastavaBecome a Hackaday.io member
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ElectronicABC
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I have uploaded the circuit of a DARK DETECTOR in files , you might wanna check it out .
In this circuit when light is incident on the LDR , it act as a LOW resistance . So the maximum current flowing through the potentiometer (variable resistance ) flows through the LDR and minimum flows through the base of the transistor . This is because of the property of current to flow in the direction of minimum resistance. Hence , base is turned OFF and the transistor acts as an open switch letting no current to pass through the LED .
While in the other case , when light is NOT incident on the LDR , it acts as a very HIGH resistance and so maximum the current passes through the base of the transistor. This turns the base ON and transistor acts as a short switch letting current pass through the LED .