LDR Light Detector

LDR Light Detector

LDR Light Detector Circuit using 741 Op-Amp

he circuit’s threshold is set by resistor VR1. When the intensity of the light falling on the LDR is lowered, resistance of that unit increases, and lowers the voltage applied to the inverting input of the 741.

LDR Light Detector circuit

R1 100kΩ
R2 100Ω
VR1 100kΩ
Q1 2N2222
RL1 9V Relay
IC1 741

The reference voltage at the noninverting input of the 741 is set (via Vr1) so that the comparator switch from low to high  when the light falling on the LDR is reduced. That high activates transistor Q1, Which causes the relay contacts to close.

Please send your ideas, which are very important for our success…

5 comments on “LDR Light Detector
  1. seetharaman says:

    Hi R2 should be 100 ohms not 100K ohms.

  2. TomPier says:

    great post as usual!

  3. kong says:

    Should be have the free wheeling diode?

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