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Make CCTV ir light LDR adjustable

Discussion in 'General Electronics Chat' started by stuee, Mar 3, 2015.

  1. stuee

    stuee Member

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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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  2. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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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
     
  3. stuee

    stuee Member

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    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
     
  4. dave

    Dave New Member

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  5. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    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.
     
  6. stuee

    stuee Member

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    Hi, ive tried the pot already a 5ook and a 1m and it made no difference?
     
  7. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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    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
     
  8. stuee

    stuee Member

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

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  9. alec_t

    alec_t Well-Known Member Most Helpful Member

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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.
     
  10. stuee

    stuee Member

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    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,
     
  11. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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    Make it look like this:
    Photocell Parallel.png
    Place the pot, as wired, across the photocell.

    Ron
     
  12. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    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.
     
  13. stuee

    stuee Member

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    thanks all, ill try that this morning and let you know the outcome
     
  14. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    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.
     
  15. JorgeF

    JorgeF New Member

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    How was the result of placing the POT across the photocell. I am interested in.
    Thanks a lot.
    Excuse my poor English.
     
  16. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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    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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