LM741ⁱ light/dark sensor with relay

The relay will be closed only when "NO light falls on LDR1", however, in testing this circuit it worked very well when the potentiometer (P1) is adjusted to a preset level of light intensity.

By swapping the positions of the 10K resistorⁱ (R1) and the LDR (LDR1), the relay will be closed when the LDR is under light.

Electronic Components< Required

 

1 x LM741 OP Amp

1 x LDR

2 x 470R 1/4W Resistor

2 x 10K 1/4W Resistor

1 x 1K 1/4W Resistor

1 x 1N4001 Rectifier Diode

1 x 10K Potentiometer

1 x 220uF Electrolytic capacitor

1 x 12V Relay

1 x General Purpose NPNⁱ transistorⁱ (200mA+)

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