Cyclic led dimmer

Discussion in 'The Projects Forum' started by b0bk, Nov 9, 2006.

  1. b0bk

    Thread Starter New Member

    Nov 9, 2006

    first post here, i'd like to have your advice on a small project i am conducting which requires that about 20-30 leds in parallel dim automatically and all together from a no light status up to their maximum brightness, then do the opposite and start again.A full light cycle from OFF to MAx ON to OFF again should be about 20-30s long.

    Something like a saw-blade shaped pattern ( down to up then down again then up etc) intensity-wise: _-°-_-°-_
    i can't ascii-draw this because the format gets lots when i post.

    Have you guys any direction to offer me? I cannot use a programmable PIC.
    Are there, by any chance, any ready made IC that can cycle power/current outputs in such a fashion?

    Thanks a lot for your kind help!

    Ian :cool:
  2. EngineerJoe


    Nov 4, 2006
    Probably the most versitile IC chip ever, the 555 timer, will provide you with the basic signal that you want. Using a transistor, you can amplify the drive current on the timing capacitor as you like. There are many references on this kind of circuit. Go to Gooooogle and type in 555.
  3. Søren

    Senior Member

    Sep 2, 2006

    Use PWM !
    If you use current dimming instead, as eJoe suggests, the LED's will vary in color temperature, most notably if they're white.

    Scroll down to: "Fading Red Eyes" on this page for a useable circuit
  4. b0bk

    Thread Starter New Member

    Nov 9, 2006
    Hi guys,

    thanks a million for your help!
    Thanks a lot for that page soren, i'm sure i'll find great inspiration from it and the fading eyes circuit is as simple as it can get ; perfect! :D