light dependant PWM

Discussion in 'The Projects Forum' started by anliath, Apr 21, 2009.

  1. anliath

    Thread Starter New Member

    Apr 21, 2009
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    Hi there, I am looking for a way to control a PWM output with LDR(s). PWM is going to LEDs to dim them (decided this was probably better than altering the current since they will be in series) such that an increase (or decrease even) in light dims the LEDs. 555 circuit seems the best, and altering the duty cycle with two resistors. Looking at it I think that I would need two LDRs, one with an inverse light resistance relationship (!?!). A bit stumped on how to do this... And if anyone one has a better solution to the problem that would be great, thanks in advance for any help you may offer
     
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
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    Can you post a schematic of what you are proposing?
     
  3. anliath

    Thread Starter New Member

    Apr 21, 2009
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  4. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
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  5. anliath

    Thread Starter New Member

    Apr 21, 2009
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    nice, frequency is preset by the astable, then the high time can be controlled on the second monostable by the LDR,

    thanks for the help
     
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