Dark Activated Switch

Introduction: Dark Activated Switch

This circuit is simple compared to other light sensitive switching circuits it switches a relay so that you can switch electrical appliances also with it, you can use the circuit for garden lamps or outdoor or indoor lighting. It contains a 10k variable resistor which controls the sensitivity of the LDR. the circuit can be made even by the beginners since it contains very few components. 

Step 1: Parts List

The circuit contains very few parts:

1          x           NE555 IC
1          x           IC socket
1          x           LDR (10K)
1          x          10K variable resistor
1          x          12V relay
1          x           Common circuit board (CCB)

Step 2: Circuit Diagram

complete the circuit according to the circuit diagram, i used an ic socket for the NE555 ic otherwise it will burn out during soldering, and the IC can be easily removed when it is damaged in future,since the circuit contains a relay the circuit can be used to switch electrical appliances also. The 10K resistor is used to vary the sensitivity of the LDR 
check the picture of the relay,
Connect 1 and 3 pins of the relay to the circuit it has no polarity  and connect  the pins 2 and 4  to the device you need to switch 

Step 3: Completed Circuit

Step 4: Conclusion

check for loose soldering if the circuit is not working,when connecting the circuit as a switch for electrical appliances the risk of getting shock is high, always use precautions when doing so.



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27 Discussions

will this work with 5v and 5v relay?

also let me know can i use electric bulb as operating device? or i have to use led for the output?

i am doing this as mini project in college, so can you help me out guys with the information asapthank you!

Can anyone tell me what is input current for the circuit

Hey, great i'ble.
I just wanted to know any tweaks in the circuit if i wanted to make a ' light activated switch'..
thank you

If anyone is having issues with the sensibility of this circuit then you could change the potentiometer to a bigger one such as 50k ohms and adjust it to around 13-15kohms as soon as you find the set point for the relay to activate then you can play with it until you get the desired activating point.


3 years ago


Please help out to making a Dark activated switc. Same above as you provide but problem is that i want making with the help of 6v battery and 6v relay.


This circuit seems to be very simple. It is not very difficult to build.

I built it twice.

Unfurtonately none of them works at all.

I doublechecked all contacts, the circuit itself. No success. I hear the relay to switch but nothing happens.

Zhe only thing I could think of the LDR. I do not understand 10k. I used 2 different types. Nothing.

Is there anybody who built it and works properly?

3 replies

Hey buddy, i just finish mine today and it works perfect, i really like how it behaves. Maybe you just using the wrong items, for the 10k ammm one is for the variable resistor and the other 10k next to the LDR is the max amount of ohms at 10 lux, i had some issues at the beginning too but i got it to work. For the LDR there're many and they do make a huge impact if you pick the wrong one. Ima post the link for the 10k LDR which is a GL5516 i bet ur using the GL5539 or a higher one. I highly recommend you this seller i never got a bad item or lost item with this seller. I get many items for him and that includes the GL5516 LDR. I hope this can help you solve the problems that ur having.


sooraj619 Thank you for this wonderful instructable nice job

Hi Kupito,
I am really happy that you had success with this circuit.
Thanks for the link where I can buy the right LDR. It will take some time to get it but I am patient.
One thing which is not clear in your explanation. If I understand well, you spoke about 2 resistors of 10 k. In the instructables.com on the circuit schema and in the part list there is only one resistor that is a 10k variable resistor. Where should I put a second one?
Best regards

It took about two weeks to get them but I bought 10 photocells from this seller for .99 cents.


how do we add a delay off to this circuit to prevent flicking during transistion?

This circuit can be really useful for me, can please post a photo of the backside of the board? Or much better yet,design a pcb for this :D Thanks very much.

4 replies

i made this circuit a year ago so i don't have any pics. sorry.. I will try designing one :D

Pls, pls do! this project can be very useful to me, Im still learning how to read schematic diagram and translating them too pcb layouts :D

Will do, thanks very much, I'm getting the hang of reading and translating schematics, this will serve as my practice.

Just a few things does this circuit run on 12volts?

And if so do you need a relay if you want to power 12 volts with it?


1 reply