Bill Marsden's "From Four, Twenty" 555 circuit

Discussion in 'General Electronics Chat' started by Garoad, Jun 24, 2012.

  1. Garoad

    Thread Starter New Member

    Apr 24, 2012
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    (BTW - for some reason I kept getting a 500 server error until I shortened the thread title, maybe there's some problem with checking for a valid thread title length.)


    http://forum.allaboutcircuits.com/blog.php?bt=681

    This is a cool idea I'd like to try, but I've always read that putting LEDs in parallel and sharing a resistor is a bad idea. Especially given that it shows some LEDs with very different Vf (red + blue) in parallel like this, is there some reason this is okay in this case? (The relatively high value resistors maybe? But wouldn't this make the blues somewhat dim?)
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The leds in that circuit are not parallel, but in anti-parallel.
    Only one led in the branch will lite up.

    Bertus
     
  3. Garoad

    Thread Starter New Member

    Apr 24, 2012
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    Whoa, I hadn't noticed that!!! That's pretty cool!
     
  4. strantor

    AAC Fanatic!

    Oct 3, 2010
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    yes it's been that way for some time. I've posted about it already a few months ago but not sure if anybody's had a chance to look into it yet.
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    If you have any questions or suggestions I am one of the regulars here (does it show?). I've been meaning to turn that design into a Christmas tree for years.

    I know of one gentleman who has used it for a Dr. Who Fan Prop.
     
  6. Garoad

    Thread Starter New Member

    Apr 24, 2012
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    Yeah that's the basic idea here too (mini tree lights).

    Q. I think D1, D3, D5, and D7 are backwards on the circuit diagram?

    Nm - attention to detail failing again, that's a Vcc they're attached to, not a ground. :)
     
    Last edited: Jun 26, 2012
  7. Wendy

    Moderator

    Mar 24, 2008
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    Like I said in the article, some are inverted versions of others, but no two are quite alike.
     
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