Light Dependent Resistors

Discussion in 'The Projects Forum' started by aussiemike, Jul 19, 2011.

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  1. aussiemike

    Thread Starter New Member

    Jul 19, 2011
    Just posted this in the other forum. Thought it might be more suitable here.

    Hi Guys,
    I am relatively new to electronic circuitry and at 60 years old am having a little trouble getting my head around some stuff.
    I started this hobby with help from a guy in Ireland called Ron jay.
    I built a few of his circuits and he has helped me enormously. I feel though I am imposing on his time and decided to come here to learn as much as I can.
    One circuit I built was a custom circuit I asked him to design for a special need.
    It can be seen here
    The idea is to get the light from the screen of a mobile phone ( Inside a dark box )to activate the LDR. Turns out the light from the phone is not strong enough to trigger it.
    Any tweeks our added circuitry I might be able to add to make this functional? In simple English please as not only am I getting old I am also an Aussie.
    Regards from Kenya
  2. Sparky49

    Well-Known Member

    Jul 16, 2011
    Hi Aussiemike,

    I think the reason might be that the LDR might not have enough resistance to 'force' the current into the IC. To solve this, try adding a resistor in series with the LDR as in this attachment.

    Hopefully, this extra resistance means the LDR can 'detect' less light before the total resistance is high enough to make the circuit work.
  3. bertus


    Apr 5, 2008
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