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WS2801 strand maximum length?

Discussion in 'RGB Lights - Intelligent Pixels and 3-Channel RGB' started by gregf, Dec 19, 2011.

  1. gregf

    gregf New Elf

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    Hi All,
    Is there a maximum number of pixels for data transfer in 5V WS2801 strands? I didn't think there was but...


    I have a 550 pixel-strand that I soldered together and am reinjecting power at pixel 256 and pixel 384. A simple test of attempting to display red on every pixel works fine (with the expected brightness differences from not injecting power more frequently) up to about pixel 384 where the colors become random (i.e. the problem). I'm running this off of an Arduino Mega 1280 so there is plenty of SRAM and I've tried several WS2801 protocol libraries so I don't think the code is the issue. I plan on injecting power more frequently but this doesn't seem to be the problem here since 384 is getting a full 5V.


    My most recent thought is that maybe some of the pixels are bad and need to be cut out. Does anyone have other ideas?


    Thanks,
    Greg
     
  2. Superman

    Superman I Have C.L.A.P and its very infectious Global Moderator

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    I found to get power to everything it needed injection every 50 pixels.
    I only run 100 per output.
     
  3. David_AVD

    David_AVD Bite my shiny metal ass!

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    Power injection is required every 50 pixels at most.

    You may be measuring 5V with a meter, but the transients during data transfer will be creating mayhem.

    Don't forget that power injection requires both the 0V and +5V wires be done, not just the +5 one.
     
  4. jstjohnz

    jstjohnz Apprentice Elf

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    I don't think there's a maximum chain length for the 2801. I agree with the other comments though, unless you have some pretty beefy wire in your pixel string there's no way you can get much more than 50 pixels without having to re-inject power. You may do better since you're only lighting up one color, but typically the voltage after 50 pixels or so is going to be well under 4 volts with all pixels lit white.

    If the issue is consistently at pixel #368 though, with differing power injection points, I would suspect a software issue.
     
  5. OP
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    gregf

    gregf New Elf

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    Thanks for the suggestions. I will try out some more power injection every 50 or so leds and report back.


    cheers,
    Greg
     
  6. riri7707

    riri7707 Full Time Elf

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    Hi,
    I confirm the needs of power injection every xx pixels, specially with 5v and 2801 manufactured strings from Ray or other vendors. Section of wire is the main key and knowing the pricing of cooper, at end we got the minimum of the minimum regarding the wires section. And more, not cooper but probably a mix of aluminium and xxx metals... :(
    I chained 84 standard strip pixels 5v, and the last 24 genetared problems. After injecting power in the middle, all was fine.
    Now, to improve these need of extrapower, i built my display myself and ws 2801 modules too : 26 lengts of 2 meters with 13 modules WS2801 each.
    Each WS2801 managee 3x5050RGB.
    So at end, i can manage 2 lines of 169 pixels (13 lenghts of 2 meters) chained (507x5050RGB) with just connecting at begin the data+clock+power and just direct re-injecting 12v from same PSU at end of the 169th pixel. All powered by a simple cheap PC power supply.
    Works perfectly, but my secret: all 2801 modules (self made) are connected to parallel wires 0.75mm2 inside each 2 meters legnth to draw enough current with 12v. So i limit the current loose and needs to inject after 50 pixels. The pcbs in this case don't suffer with current draw as they keep just the power they need from the line.
    At end : 2 cables for 26 meters lenght that's it.
    Here, as i built a mural tree, i have 2 injections at begin with data and clock and 1 at end of each portion of every 26 meters for a total of 52 meters and a single PC PSU 550w.
    I'll put some picutres asap.
    338 x WS2801
    1014 x 5050 RGB
    Cheers....
    Henri
     
  7. OP
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    gregf

    gregf New Elf

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    Wow, Henri that sounds awesome. Please post some pics!


    Are you using a microcontroller to drive the data and clock? If so, what clock speed are you using? I figured out that my problem (after trying more power injection :) ) was due to trying to send data at 2Mhz. If I drop the speed to 1Mhz, things work fine albeit more slowly than I'd like. :( Does this make sense?? I can't wrap my head around it at the moment.


    Also I'm not sure what you mean by a parallel wires. Could you explain further?


    Greg
     
  8. riri7707

    riri7707 Full Time Elf

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    Hi Greg,
    I use EThCong P12R from ED.
    After LSPv 2 makes the magic lights :)

    For the clock i think it's only 750 Khz per universe, as default value...
    Never try to go over this value...

    i'll put some pictures soon and a video, promised ....

    Regards

    Henri
     

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