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RPi + Other Software Flicker on white screen when adjusting color/whitelevel

Discussion in 'Software Support' started by Bob M, 8 July 2019.

  1. Bob M

    Bob M New Member

    Messages:
    14
    Hardware:
    RPi3
    I'm posting this on the Software Support forum, though I'm expecting the answer *could* be power related.

    I have 88 WS2801s connected to a Pi3 via SPI and a level shifter. I'm running a HDMI splitter and utv007 capture which works fine. My PSU is 10A and although it also powers the Pi and HDMI splitter I *think* it's powerful enough.

    I'm supplying power at both ends of the strip. When I was previously supplying only 1 end, the LEDs gradually became slightly yellow-ish towards the end, but there's also always been a slight red tinge (on all LEDs) when display a full white picture. However the LEDs are stable - no flicker.

    If I change the color adjustment settings - whitelevel, gamma, etc, even by the smallest amount (when displaying the white picture) - all of the LEDs start to flicker wildly. Which seems wierd - if I reduce the red value on "whitelevel" for example, surely the LEDs require *less* power and so should remain stable? But I get the wild flickering. So this got me to thinking that it's not a power issue.

    But! I've found that if I set "Luminance gain" to 0.8 and therefore reduce the overall brightness, then I can adjust the color values without getting any flicker - which seems to point at a power issue!

    So I can live with the slightly red hue to the colors or reduce the brightness. I'm happy enough to run with 0.8 Luminance so this isn't really a big deal, but I'd love to understand what's causing the issue. Any suggestions?
     
    Last edited: 8 July 2019
  2. kevinlekiller

    kevinlekiller New Member

    Messages:
    4
    Hardware:
    RPi2
    Do you have a wiring diagram of how you wired it? I had the same flicker issue, had to put the level shifter real close to the first led (about 5cm), also put the power at the 4 middle points, and use a separate power supply for the pi, have about 230LEDs with 15a supply, no flicker. Crude wiring diagram uploaded.
     

    Attached Files:

  3. Bob M

    Bob M New Member

    Messages:
    14
    Hardware:
    RPi3
    Thanks for the diagram!
    So the one glaring difference with mine is that there's a few metres of cable between my levelshifter and the LEDs - I added the shifter explicitly so that I could have a longer cable length, but it guess it could be the issue. I'll remove the extra cabling and see if it makes a difference.
    I guess I should look at adding extra 5v cables too, it can't do any harm... though I'm measuring 5v (+/- a few percent) throughout the stip. Ha, that said I don't think I measured while the LEDs were at full white, so definitely worth re-measuring.