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Auto Dimming Circuit

Discussion in 'General Electronics Discussion' started by Just Bob, Feb 15, 2013.

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  1. Just Bob

    Just Bob

    1
    0
    Feb 15, 2013
    Howdy.
    I'm new to EP and very appreciative that this site is on the web. Thank You.

    I've been searching the web for a circuit to auto dim a string of 15 led's. I must be typing the wrong key words or something.

    Here is my dilemma.

    I would like the led's to be bright during the day, and dim at night automatically. A gradual dimming would be great and adjustable low dim point.


    I'm just learning about transistors and pretty good at soldering.
    I'm only on the 4th experiment in my 300 in 1 electronics kit.

    Thank you now for any help available. Les
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    Look for circuits that do PWM control of the brightness of a string of LEDs.

    Now look for an oscillator where you can change the duty cycle with a single resistor (I'd be looking at a 555).

    A series and a parallel resistance (to an LDR) to provide an effective minimum and maximum resistance and you're gold.

    You will find that with a 555 and a single resistance (that changes) you will only change the mark or space, so the frequency will change as you change duty cycle, bit that's not going to be too important as long as the minimum frequency is maybe 100Hz and the maximum maybe around 10 kHz range. (this range will keep you out of tricky regions).
     
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