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Thread: Help with first setup

  1. #11
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    Default Re: Help with first setup

    Quote Originally Posted by MartinMueller2003 View Post
    Sigh. I have ranted on this many times V- and Data MUST travel together at all times. They must experience the same conditions, the same noise, the same world view. The pixel input is data with respect to ground (aka V-). If the ground reference does not match exactly the conditions the data wire experiences, then noise is introduced into the system and you get a pretty flashing that you do not want.
    Sorry, but i don't fully understand how they can travel together. V- and Data run together through the pixels, but what happens when you inject power and have a new V- added in? Does this not alter the ground reference?

    My setup would probably be something similar to this:


    With a power supply for the raspberry Pi and a separate one for the pixels.
    V- from the pixel power supply is connected to Ground on the Pi output.

    I have since tried another level shifter and had similar problems with interference.

    I then tried removing the level shifters altogether and ran data straight from GPIO18 on the Pi. Not recommended i know, but it's resolved the issues. Perhaps this can get my through this Christmas, then i'll have time to figure out a better option and get a controller for next year.

  2. #12
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    Default Re: Help with first setup

    Quote Originally Posted by TomD View Post
    Sorry, but i don't fully understand how they can travel together. V- and Data run together through the pixels, but what happens when you inject power and have a new V- added in? Does this not alter the ground reference?

    My setup would probably be something similar to this:


    With a power supply for the raspberry Pi and a separate one for the pixels.
    V- from the pixel power supply is connected to Ground on the Pi output.

    I have since tried another level shifter and had similar problems with interference.

    I then tried removing the level shifters altogether and ran data straight from GPIO18 on the Pi. Not recommended i know, but it's resolved the issues. Perhaps this can get my through this Christmas, then i'll have time to figure out a better option and get a controller for next year.
    You might just want to get a PiHat. It's basically the concept you're going for (driving pixels straight from a Pi), but has the data buffered and all the signals routed for easy connection. They're simple and inexpensive. Then if you decide to move forward, you can always spring for a more expensive board (or just stick with PiHats, like many people have done).

  3. #13
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    Default Re: Help with first setup

    I agree a pihat would make this a lot simpler. My issue is they're not readily available in the UK which is why i'm trying out a very basic approach before diving right in.

    I'm also at the bottom of a cul-de-sac, which means not many would get to see any kind of display i might do. Kind of puts me off wanting to do too much unfortunately

  4. #14
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    Default Re: Help with first setup

    Quote Originally Posted by TomD View Post
    Sorry, but i don't fully understand how they can travel together. V- and Data run together through the pixels, but what happens when you inject power and have a new V- added in? Does this not alter the ground reference?

    My setup would probably be something similar to this:


    With a power supply for the raspberry Pi and a separate one for the pixels.
    V- from the pixel power supply is connected to Ground on the Pi output.

    I have since tried another level shifter and had similar problems with interference.

    I then tried removing the level shifters altogether and ran data straight from GPIO18 on the Pi. Not recommended i know, but it's resolved the issues. Perhaps this can get my through this Christmas, then i'll have time to figure out a better option and get a controller for next year.
    In your picture, you are showing that data and V- both leav the controller and arrive at string #1, pixel #1. THis is good. You then show that data and V- both leave the last pixel on string #1 and go to the first pixel on string #2 This is good. Many people try to skip the V- that runs from the controller to string #1, pixel #1. That causes no end of problems.

    In the case of the pixel buffer/level shifter. You needed to have three wires from the PI: 5v, Data and PI V- going to the buffer and two wires Data/V- going from the buffer to string #1, pixel #1. If you did that then things should have worked just fine. The distance between the PI GPIO and the buffer should have been as short as possible.

    For your question: Sorry, but i don't fully understand how they can travel together. V- and Data run together through the pixels, but what happens when you inject power and have a new V- added in? Does this not alter the ground reference?

    Yes it does alter the reference a bit. The key is distance. When the distance between the sending and receiving entities is short (less than a few feet) then the difference in the reference voltage tends to be small enough that the pixels dont get saturated with noise. When the distance gets larger (over 4m), the loss of reference and the degradation in the data signal becomes too much for the receiving pixel to correct and you get flickering. Wire quality is a big factor here. Using a shielded cable to transport the V- and Data signals can significantly extend the distance the signal can travel before it degrades too much to be useful.


    2020 Full sized show reworked for the new location. Only adding (famous last words) 13 RBLs that I finally got converted to using pixels
    2019 - Just moved into a new home (yet another change of plans). Will be dim but not dark. Too much to do at the new place to leave time for a show. Dim show (3000 pixels) had regular visits most nights.
    https://www.youtube.com/channel/UCyX...ttrsZNARkUce0Q

  5. #15
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    Default Re: Help with first setup

    Just to provide an update on this. I have bought a new PSU and now have no interference when using the level shifter.
    The old one was a black brick type, 5V 10amp.

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