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Make CCTV ir light LDR adjustable

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stuee

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Hi, I posted a bit back about turning my cctv ir sensors into adjustable and someone suggested a 100k trim pot, ive tried different values etc ad no joy.

Could someone help me as ive been in touch with Chinese suppliers and they either dont understand or help.

I have attached the photo of the board, i would like ideally to add a trimpot so i can adjust to its location and do the same on other cameras.
i did do a reading on the ldr and got the reading Full light 500 ohm and dark 1.3m I would have measured wrong and if so let me know the correct way.

thanks in advance.
 

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My understanding is currently the IR intensity is controlled by the photocell in the image posted. You want to eliminate the photocell and manually use a potentiometer to adjust the IR intensity? Should that be correct then I would try removing the photocell and replacing it with a 1 Meg pot in series with a 500 Ohm resistor as shown below:

Pot String.png


The 500 Ohm is approximate, something like 510 Ohm off the shelf would be fine. For the 1 Meg I would look for a linear 10 turn 1 Meg pot.

Ron
 
Hi Reloadron, thanks for the reply.
Im not trying to eliminate the photocell, i just want it to turn in the ir / filter when its a bit more darker as when the sun goes behind a cloud the some of the cameras constantly click on colour and night vision, also at night when there is people in the room and the light is on its just not getting enough light to keep colour but when it actually does flick to colour briefly i can see there is plenty of light for colour to see everything perfectly fine.

cheers
 
Try doing as ron says but put the pot in parallel with the cds photocell, then the circuit will think its brighter out than it reall is and hold off the ir night vision.
 
While I like the suggestions of Dr. Pepper when you used a 100K pot how was it added to the circuit? Was the added trim pot in parallel or in series with the existing photocell? Since under full light the photocell measured about 500 Ohms and in Darkness it measured greater than or about 1.3 Meg Ohm you want to trick the system into believing there is more light than there actually is as seen by the photocell. As Dr. Pepper mentions there is a comparator in there and when a certain preset level is attained it switches. You could look at the signal to the IR Cut Filter and see what voltage levels you have under various lighting conditions? Note where the transition happens.

Ron
 
so i put like this
hope it makes sense as my paint skills are pretty bad :)
 

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No, you've shown the pot in series with the cell. As the others said, the pot needs to go in parallel with the cell.
 
sorry for being a little dupid, how would i hook up parallel with the cell, also would it make a difference which side of the cell its connected on,
 
Make it look like this:
Photocell Parallel.png

Place the pot, as wired, across the photocell.

Ron
 
Try a 1 meg, if it doesnt work that well, or the pot is really sensitive then remove the photocell from the board, put it where it would be used at about the same light level and measure the resistance with your multimeter, then you need a pot that is 5 to 10 times the resistance.

Nice diplomacy ron.
 
another idea, take a pair of sunglasses and put it in front of the sensor. If it works trim to fit. I did that with a automotive day/nigh mirror/

Mirror was too dark after the "technology" , new glass with different electrochoics, was updated.
 
How was the result of placing the POT across the photocell. I am interested in.
Thanks a lot.
Excuse my poor English.
 
How was the result of placing the POT across the photocell. I am interested in.
Thanks a lot.
Excuse my poor English.
You would do better to start a new thread, this thread is a few years old. Start a new thread and ask your questions regarding a pot in parallel with a photocell. Also, welcome to the forums.

Ropn
 
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