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Lightning effect using leds

Discussion in 'Electronic Design' started by [email protected], Jul 8, 2007.

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  1. Guest

    Hi, I a total hobbiest so forgive me I if seem blatantly ignorant,
    because I am. I initially thought I could create a really cool
    lightning effect using white leds wired in series with a capacitor and
    resistor at each LED. Essentially the effect is a chaser that starts
    a fixed point and branches outward at uniform speed but only repeats
    on command.

    Now I see some complication in the RC time approach that I don't know
    how to solve cheaply. I'd like to string 50-100 LEDs together to
    make a nice long branchy bolt of mother natures finest.

    I'm also toying around with using a NAND gate such as described in
    this chaser recipe: It
    should be possible to replace the 10th LED in the sequence with a
    pullup that goes into pin 14 of another NAND gate and so on and so on.

    Any and all advice greatly appreciated.
  2. D from BC

    D from BC Guest

    I have a bloated idea :)

    Binary counter + DAC + voltage controlled power supply + resistor +

    Make the step size the same as an LED voltage drop.
    D from BC
  3. Use a PIC, of course.

    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: email:

    Please visit my GURU's LAIR web site at
  4. How about filling up a buch of series connected shift registers with 1?
    Reset will clear, but maybe just reverse.

  5. Tim Shoppa

    Tim Shoppa Guest

    You need some sort of negative-resistance effect to get the LED's to
    turn off in sequence, and you don't have that with just LED's, R's,
    and C's.

    You could put, say, a unijunction transistor at each LED to have it
    switch on when the previous one switched off, and then daisy chain
    them all. But this isn't 1968 anymore, so you'd do all the switching
    with 555's or a microcontroller or something like that.

    If you're looking for light-emitting devices with useful negative-
    resistance slopes in their curves, take a look at neon bulbs. For

  6. Not a bad idea. HC595 or something like that. Use ULN28033 if you want
    to be able to drive a bunch of LEDs @20mA off of each output for the
    branches. Say 5 of each chip to drive about 40 outputs. Watch the
    layout, with 100 LEDs @20mA you have a couple of amps, and switched
    fairly fast. Another reason to use drivers and keep the power ground
    layout sensible.
    Something at the end for terminating the sequence-- maybe the last bit
    sets an SR FF which clears the SR and holds the 555 in reset.

    JF seems to like ironing out the details and drawing up proper
    schematics for these things.. maybe this would interest him (or not).
    And sound FX. Or stick with a pushbutton; less programming!

    Best regards,
    Spehro Pefhany
  7. Guest

    1) It's spelled "hobbyist".
    2) Go to your local equivalent of a dollar store. You can buy a fiber
    optic tree with RGB LEDs. You just press the button and it cycles
    through all kinds of color variations.
    3) Problem solved.
    4) Drink beer.
  8. Guest

    Yeah, hmmm.... thanks for the spelling correction, I ignored
    firefox's built-in indication. And yeah, while that might work for
    you, you obviously don't know me and have no idea the lengths to which
    I will go to see a vision through. Different sorts I guess - you the
    anal retentive spelling bee with a great sense of how to relax and me
    the over obsessive, too concerned with other pursuits to care about
    spelling and grammar. But hey, it's all good.
  9. Guest

    Thanks to everyone for the suggestions; you were very helpful. I
    have done some other projects using a Basic stamp and with the
    suggestions to use a PIC, it was clear how simple it would be to use
    an output pin on the BS2 to strobe the clock pin on the 4017. The
    code is so simple, just stobe pin 0 10 times, followed by pin 1,
    etc. 15 pins (1 pin for mech trigger switch) out equals 150 lights
    that can be fired in sequence. The branches in the bolt can just be
    programed into the BS2.
  10. Guest

    The vision of a LED chaser. Good to have dreams and aim high....
    Don't forget to make your own PCBs too.
  11. neon


    Oct 21, 2006
    LEDS are not as good or cheaper then xmas lights you want something cool try music driven kights with proper filtering you amy actualy see the spctrum as music play. easy to inlement run off the line and the power i 5watts. you need an opisolatorwith scr out and a 600v triac and you got it simple enough.
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