ldr sensor circuit

Dark sensor circuit – 4 circuit

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 how to make darkness circuit (4 circuits)

1. LDR Darkness circuit diagram using 555 

ldr circuit diagram



1000uf 25v -1

10uf 25v -1

0.01 uf -1


1KΩ – 3

LDR – 1

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

1N4007 diode – 1

IC 555 – 1

Transistor – 2N2222A- 1

Relay 6V – 1

Preset 1MΩ – 1

2. LDR Darkness circuit using the comparator 

√ Tested

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_PCB_ldr


darkness sensor ldr circuit

ldr darkness circuit

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.

√ Tested

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 darkness circuit.


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