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Thread: Finally Affortable Snowfall Tubes (FAST)

  1. #11
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    Default Re: Finally Affortable Snowfall Tubes (FAST)

    Quote Originally Posted by n8huntsman View Post
    Check out pages 8 and 9 of this for a good schematic and explanation of charlie-plexing. This really helped be get my head around it.
    http://downloads.eshepherdsoflight.c...d-MidiTree.pdf
    Actually, that is just an example of multiplexing, rather than Charlieplexing. With Charlieplexing, the state of each output effects the resultant selection, where in DonJ's megatree, each of 12 outputs controls a branch, while two outputs are used to select one-of-four colors for all branches.

    Charlieplexing will light (or not light) one of two LEDs (or strings) for EACH PAIR of outputs. For example, (for two outputs) If A is high and B is low, then D1 lights; if A is low and B is high, then D2 (which is wired back-to-back with D1) lights. If A and B are both high or both low, then neither D1 nor D2 light. Again, the rule is N*(N-1) lights for N outputs. In this example, 2*(2-1)=2. The advantage comes when you build up the number of outputs feeding the matrix.

    However, as you increase, you lose discrete control, unless you can tri-state (open-circuit) the outputs. Lacking that capability, for 8 bits of data, you can control 8*(8-1)=56 lights. Since there are 256 possible states (ON or OFF) of 8 bits, there are only two states with all lights off (00000000 and 11111111). All other bit patterns will result in 7, 12, 15, or 16 lights on. Actually 7 occurs 16 times, 12 occurs 56 times, 15 occurs 112 times, and 16 occurs 70 times. Each light is on in 64 of the 256 states.

    (Isn't matrix math fun????) :roll: :roll: :roll: :roll:

    As usual, I've gone on way too long, but that's me... (see my signature):D
    Last edited by WireWrap; 04-20-2011 at 05:00 PM.
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  2. #12
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    Default Re: Finally Affortable Snowfall Tubes (FAST)

    Quote Originally Posted by WireWrap View Post
    Charlieplexing will light (or not light) one of two LEDs (or strings) for EACH PAIR of outputs. For example, (for two outputs) If A is high and B is low, then D1 lights; if A is low and B is high, then D2 (which is wired back-to-back with D1) lights. If A and B are both high or both low, then neither D1 nor D2 light. Again, the rule is N*(N-1) lights for N outputs. In this example, 2*(2-1)=2. The advantage comes when you build up the number of outputs feeding the matrix.

    However, as you increase, you lose discrete control, unless you can tri-state (open-circuit) the outputs. Lacking that capability, for 8 bits of data, you can control 8*(8-1)=56 lights. Since there are 256 possible states (ON or OFF) of 8 bits, there are only two states with all lights off (00000000 and 11111111). All other bit patterns will result in 7, 12, 15, or 16 lights on. Actually 7 occurs 16 times, 12 occurs 56 times, 15 occurs 112 times, and 16 occurs 70 times. Each light is on in 64 of the 256 states.
    Also, by adding bipolar transistors across the resistors, you can increase the I/O pin drive capability so that you can turn on multiple LEDs within a "row" of LEDs without burning out the I/O pin. An EDN article about "chipiplexing" a while back described that trick.

    don
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  3. #13
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    Default Re: Finally Affortable Snowfall Tubes (FAST)

    Quote Originally Posted by djulien View Post
    Also, by adding bipolar transistors across the resistors, you can increase the I/O pin drive capability
    Of coarse as you know, using an appropriate optocoupler will allow you to drive nearly anything you want.
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    Default Re: Finally Affortable Snowfall Tubes (FAST)

    Quote Originally Posted by ErnieHorning View Post
    Of coarse as you know, using an appropriate optocoupler will allow you to drive nearly anything you want.
    I was thinking that optocouplers are used more for voltage isolation, but that's an interesting idea to use them for current protection purposes also. thanks.

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    Default Re: Finally Affortable Snowfall Tubes (FAST)

    pretty neat
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    Default Re: Finally Affortable Snowfall Tubes (FAST)

    Ok, I got my LED's in from the group buy and away I go.. Here are some pics of my first one.. Being that I'm lazy and cheap I didn't feel like going to the store and getting any formica to start this project. I had an old screen out of an old rear projection tv in my garage. The diffuser on the front of the fresnel lens has nice groves in it perfectly positioned to run a razor blade down it to score it and snap to the width I wanted. The screen I'm using happens to be around 24" tall If I want different size tubes I just find larger screens. People are always throwing these TV's away now what I nice way to recycle part of them. On a side note the Fresnel lens is very fun to play with but very dangerous. WARNING : It'll make a spot and get it 2000+ degrees.. You can melt glass and or steal or give yourself a nice sunburn.. So here are some pictures of what I've completed so far.. Not pretty but functional and the screen was free.

    FAST1.jpg
    FAST2.jpg
    FAST3.jpg

  7. #17
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    Default Re: Finally Affortable Snowfall Tubes (FAST)

    Looks great so far. Hope to see the finished product by monday, and of course we will need video of it actually working so we can all want to do it.
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    Default Re: Finally Affortable Snowfall Tubes (FAST)

    Quote Originally Posted by tweist View Post
    Looks great so far. Hope to see the finished product by monday, and of course we will need video of it actually working so we can all want to do it.
    +1

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    Default Re: Finally Affortable Snowfall Tubes (FAST)

    Hi, trying to follow along with the schem.
    All the LEDs in both drawngs are labled D?
    Although the color "wiring"diagram helps, still not sure what sequence to wire the LEDs.

    Oh, btw, I am planning on using 3/4" green plastic Banding tape we use at work. We throw thousands of scrap pieces away daily...
    If anybody wants to try ths flexible pcb, pm me
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  10. #20
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    Default Re: Finally Affortable Snowfall Tubes (FAST)

    Hi all, been semi-away for a bit.

    I just came back from Home Depot after my weekly drool-fest in the store.

    Flourescent tube covers.. about 2 bucks each and up to 4 feet long. They are clear and have caps on each end with an opening to allow the prongs to poke through.

    Use those and a small pcb board for the hardware and run a ribbon-cable (or even a pair of cat5 cables) off the board and the leds soldered to the ribbon. a small elastic band keeping the ribbon cable taunt at the bottom, in the same fashion as the di-pole antenna tensioner.

    Could not find a HD sku number online, but here is a UK store with the same items..



    Last edited by Aurbo99; 05-08-2011 at 08:54 AM.
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