L20, Dark/Light Sensor Using Transistor



It’s the circuit of light sensing/detector, when LDR senses the darkness or lightness LED will glow. As the light level decreases and LDR meets the maximum threshold resistance, the circuit automaticallySwitch on the LED D1.

Dark sensor with variable resistor:

A dark detector can be made using a variable resistor. The sensitivity 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.


Automatic Light detector using variable resistor –

A light detector senses light. As the light level increases and LDR meets the lowest threshold resistance, the circuit automatically turns on the LED D1. We can adjust the sensitivity using the preset VR1-10K.

less resistance - less darkness to switch off the led

high resistance - more darkness to switch off the led

Components-

  • 9volt battery + 7805

  • Transistor BC547

  • Resistors R1 = 470, 330 ohm

  • Resistors - 1k, 100k

  • LEDs

  • Light dependent resistor (LDR)

  • Variable resistors 10k, 100k

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