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ldr sensor circuit

Dark sensor circuit – 4 circuit

 how to make darkness circuit (4 circuits)

1. LDR Darkness circuit diagram using 555 

These circuits uses directly 230v AC.  so careful when testing

ldr circuit diagram



105J 400V – 2

470uf 25v -1

10uf 25v -1

0.01 uf -1


220Ω 1W – 2

470KΩ – 2

1KΩ – 3

LDR – 1

Bridge Rectifier -1 or 1N 4007 diode – 4 pc for making Bridge rectifier

1N4007 diode – 1

IC 555 – 1

Transistor – BC547 0r 548 0r 549 – 1

Relay 5V – 1

Preset 1MΩ – 1

2. LDR Darkness circuit using the comparator 

ldr sensor circuit

Note- LDR must keep away from the light of the load bulb for flicker less operation. You can do this using the covering of the side area of LDR using black tape.

Demo testing Video Of LDR Darkness circuit using the comparator 





510Ω or 470Ω -1

56K-1 (Not compulsary)


 1000uf 25v-1

220nf (224)-1

C2 = 220uf or 100uf 25v-1

Variable resistor 22K-1




0-6v 500ma- 1


LM358 (comparator)-1

MOC3021 (optocoupler- 1

Transistor BC548-1

Triac BT138-1

LDR (12mm)-1


Download Gerber.dark sensor.zip

Download PCB layout 

3 &4 . Photodiode darkness circuit diagram

This circuit diagram is made using the photodiode as the light sensor or dark sensor with the lm358 comparator. Highly sensitive and flicker less.

photodiode darkness circuit diagram

Video of photodiode dark sensor circuit


As my testing experience, Although Both LDR and Photodiode based circuit works well But The LDR based circuit is better than photodiode based circuit.

About the Author


Hi, My name is Aman Bharti, I am interested in making and study of Electronics, circuit diagram, PCB designing and layout etc. I like to share the knowledge and all ideas with people which I get from My Experiment & from different sources. I try to provide any circuit details deeply with test results as possible. If you want to give a suggestion or comments on anything, please leave your comment in the comment box of the related page.

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