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Thread: Erratic WS2811 Strands

  1. #1
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    Default Erratic WS2811 Strands

    So, I've got an interesting one. I have an E6804 running to a strand of WS2811 and I get very erratic results--until--I touch the solder connection on the data wire, between the board and the strand. And by touch, I mean with my finger. Then it works perfectly.

    I've tried wiggling the wire to see if it's just a bad connection, and I'm pretty confident it's a nice soldered connection. And this is the 3rd time I've rewired (even reducing the initial run length). The run from the E6804 to the first pixel is only about 2 feet.
    Any ideas? I'll post a video in a bit, as a visual may help.

    Thanks for any help!
    Brian

  2. #2
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    Default Re: Erratic WS2811 Strands

    How long is the run between controller and the first pixel? When I see this I start thinking about adding a NULL Pixel / Buffer / Driver. You might want to adjust the output resistor to a different value (i hate doing this and prefer the driver route). When you touch a connection like that you are adding capacitance that reduces the reflected echo / noise on the wire (cleans up the signal). Echo is caused by an impedance mismatch. Wire impedance is a function of wire gauge, insulation quality and wire length. Adding a NULL Pixel / buffer / driver to the wire at a point before the signal degrades too much tends to relieve the symptoms (not "fix" it).

    2017 adding 2 more candy canes, 7 Mid trees and a Halloween show. Removing most 2812 strips and replacing them with bullet pixel mounting strips. Replacing many buck converter waterproof bags with printed boxes.

  3. #3
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    Default Re: Erratic WS2811 Strands

    The run from the controller to the first pixel was only about 2 feet, but for some reason it wasn't working right. I put a pixel right off the board and connected it to the same wires to the rest of the strand and it seems to have done the trick. Still not sure why it was doing that, but at least you helped me find a workaround. Thanks a bunch!

  4. #4
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    Default Re: Erratic WS2811 Strands

    i remember having problems a while back if i had pixels connected too close to a 681. Putting an extension cable in line before the pixels helped to clear it up. changing the resistor packs to 100 ohm also helps.

  5. #5
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    Default Re: Erratic WS2811 Strands

    Quote Originally Posted by jchuchla View Post
    i remember having problems a while back if i had pixels connected too close to a 681. Putting an extension cable in line before the pixels helped to clear it up. changing the resistor packs to 100 ohm also helps.
    I'd speculate that the output circuit switched very rapidly (rise time) that the wires acted as inductors for those high frequency thus caused ringing. A large capacitance can swamp it but it would also reduce the risetime too much if the capacitance is too high. A series resistance can help to dampen the ringing and make the output more squarewave like. Line driver designs go into these parameters and optimize them for taming the parasitic elements.
    Last edited by LightUp; 12-07-2017 at 06:17 PM.

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