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Lightning effect using leds

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:

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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.

Reply to
bryanwilkerson
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I have a bloated idea :)

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

Make the step size the same as an LED voltage drop. D from BC

Reply to
D from BC

Use a PIC, of course.

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Many thanks,

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

On a sunny day (Sat, 07 Jul 2007 22:46:36 -0700) it happened Don Lancaster wrote in :

How about filling up a buch of series connected shift registers with 1? Reset will clear, but maybe just reverse.

. .. ... ..... .... ... .. . Add 555 timer as osc, a flop-flip. Use the PIC for generating random starts :-)

Reply to
Jan Panteltje

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 example:

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Tim.

Reply to
Tim Shoppa

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

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"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Reply to
Spehro Pefhany

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.
Reply to
a7yvm109gf5d1

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.

Reply to
bryanwilkerson

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.

Reply to
bryanwilkerson

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

Reply to
a7yvm109gf5d1

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