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quick question about cds cells

Discussion in 'Electronic Design' started by audiogroove, Oct 9, 2006.

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  1. audiogroove

    audiogroove Guest

    I was wondering if you use a cdS cell (cadium sulfide resistor) in a
    circuit, does the circuit consume any power when it's in a completely
    dark environment? Does the battery get wasted even though the circuit
    is completely in the dark? I am thinking if the cell is used with a
    relay to control on/off power to the circuit.


  2. Since the dark resistance is lower than infinite ...

  3. Eeyore

    Eeyore Guest

    What do you mean by 'circuit' ?

    The cell itself consumes no power.

  4. Most cdS cells have really high dark resistance, many megohms. So
    depending on the voltage across it, the dark current is likely to be
    quite low, microamps or so.

    Why not measure the cell with an ohmmeter and see (well you wont be
    able to see it, hmmm......) ?
  5. The dark resistance is usually pretty high, so dark current
    should be very low. But you have to think about all light
    levels between darkness and the brightest the light can be.

    A battery saving approach might be to use a small (low
    current CDS cell or photo transistor and a comparator (i.e.
    LM393) to measure the light level and make the on off
    decision to operate the relay.
  6. Genome

    Genome Guest

    Since there are some thick dudes in this newsgroup who are still suffering
    from the delusion that since you posted a question you know what you are
    talking about and will then waste their time giving you some answers.....

    What the **** are you talking about?

  7. Robert Baer

    Robert Baer Guest

    The EU commissionhas determined that your question does not conformto
    RoHS regulations and requests that you submit yourself to its tender
    mercies via Gill O. Tine.
  8. jasen

    jasen Guest

    no, but to get completely dark you'd need to cool it to absolute zero
    (to exclude all infrared)

    if you just mean in a dark room or closed box it will have finite resistance
    and,therefore, conduct a little.

    the full question though depeds on ther circuit. I have a nightlight with a
    CDS cell, and that circuit consumes more power in the dark than in the light.

    also, a typical CDs cell won't conduct well enough to operate an ordinary
    relay by itself.

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