Dark/Light sensor using transistor | BUILD CIRCUIT

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Dark/Light sensor usingtransistorPosted by: Sagar Sapkota on November 8, 2010 in Basic Electronics, circuit-blog.com, LDR Engineering, MINI Breadboard 67 Comments

Automatic dark detector senses darkness. As the light leveldecreases and LDR meets the maximum threshold resistance,the circuit automatically switches on the LED D1.

Dark/Light sensor using transistor | BUILD CIRCUIT

file:///C|/Users/acer/Desktop/project/a/Dark_Light%20sensor%20using%20transistor%20_%20BUILD%20CIRCUIT.htm[4/12/2013 12:01:01 PM]

Dark sensor with variable resistor:

A dark detector can be made using a variable resistor. Thesensitivity of the circuit can be adjusted with a variable resistor.

High resistance-> more darkness to switch on the LED.

Low resistance-> less darkness to switch on the LED.

Dark/Light sensor using transistor | BUILD CIRCUIT

file:///C|/Users/acer/Desktop/project/a/Dark_Light%20sensor%20using%20transistor%20_%20BUILD%20CIRCUIT.htm[4/12/2013 12:01:22 PM]

Automatic Light detector using variable resistor

A light detector senses light. As the light level increases and LDRmeets the lowest threshold resistance, the circuit automaticallyturns on the LED D1. We can adjust the sensitivity using thepreset VR1-10K.

LESS RESISTANCE(VR1)-> LESS DARKNESS TO SWITCHOFF THE LED

HIGH RESISTANCE(VR1)-> MORE DARKNESS TO SWITCHOFF THE LED

Just swap the resistor and LDR to convert a dark sensor toa light sensor

Dark/Light sensor using transistor | BUILD CIRCUIT

file:///C|/Users/acer/Desktop/project/a/Dark_Light%20sensor%20using%20transistor%20_%20BUILD%20CIRCUIT.htm[4/12/2013 12:01:44 PM]