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Thread: Underground Null Pixels

  1. #31
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    Default Re: Underground Null Pixels

    The shield is your signal ground it should be connected at both ends to the power ground.
    In 3 wire pixels, the signal ground and power ground are the same thing. But if running them on separate wires, you need to bond it all together.


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  2. #32
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    Default Re: Underground Null Pixels

    Respectfully disagree jchuchla. If you ground both ends, it is a circuit, but not a shield, audio uses both ends grounded, because it is a balanced circuit. Noise grounds are single ended.
    Ground shield at data source side, data line is center. Keep your old power wires if they were sufficiant.
    Last edited by aknflyer; 04-20-2017 at 01:13 AM.

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  4. #33
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    Default Re: Underground Null Pixels

    Quote Originally Posted by aknflyer View Post
    Respectfully disagree jchuchla. If you ground both ends, it is a circuit, but not a shield, audio uses both ends grounded, because it is a balanced circuit. Noise grounds are single ended.
    Ground shield at data source side, data line is center. Keep your old power wires if they were sufficiant.
    I agree with your statement, however It shouldn't be handled as a shield, but rather as a conductor. It should be part of the circuit. The intent here is not to shield an unbalanced signal wire from external interference, it's to maintain circuit impedance. Just like a video line. Shield is connected at both ends there. A data circuit is still a circuit, and even if you have another conductor duplicating part of the circuit serving another purpose (power return), it doesn't negate the need for that member of the circuit to participate in the data transmission line as well.

  5. #34
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    Default Re: Underground Null Pixels

    I see your point jchuchla, you may be correct for pixel data.
    I am a newbie with pixels. But 38 years in electronic, avionics, telecom technician.
    So which impedance is best? 50Ω or 75Ω ? I am sure on some of my long runs I may need that info when I get to that point.

  6. #35
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    Default Re: Underground Null Pixels

    I've found that they run best around 100-120ohm. Which coincides perfectly with cat cable.
    I personally haven't done pixel runs in coax. Mine have all been on twisted pair. Both balanced and unbalanced configurations. But even in unbalanced, I've always seen better performance when that unused conductor in the data pair is bonded to ground on both ends.
    I did play with coax a while back when I was trying to mitigate noise emissions from pixel lines, it worked fine to drive the pixels, but didn't go far enough to mitigate the noise so I abandoned the idea since Is much less convenient to work with and more expensive than cat cable anyhow.


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  7. #36
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    Default Re: Underground Null Pixels

    Hey everybody,

    I've been taking a break from the lights because I've been unable to stop the flickering. I'm content now with abandoning running the data cables underground. I'd really love to just get the lights functional without flickering. I bought a box of cat 5 cable and would like some guidance on how to wire up my display with it. I found lots of different opinions online. Is there anything else I should be looking into regarding the flickering lights?

    Thanks,

    Ben Roy

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