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Thread: WS2811 flicker but only at low brightness - Help please?

  1. #1
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    Default WS2811 flicker but only at low brightness - Help please?

    Hello all,
    Firstly, thank you all for a fantastic forum. This will be my second year in the UK with pixels and whilst this is my first post, I've used the forum for many resources already. We have expanded for the second year, and this is where the problems started - please help. (And sorry for the long post)

    I've searched for the same problem but can not find the exact problem we have. I have tried many of the fixes for similar problems but nothing has worked and we are at our wits end.

    With some left over 1st year ws2811 5v pixels we made 4 x matrix panels- each 30x33 pixels spaced at 25mm. The string zig-zags up and down panel. 2x matrix used ws2811 from one supplier (on Ebay) and 2 matrix used ws2811 from a different supplier on Ebay. Each panel is driven from a single F16v3 data output. Power is injected every 66 pixels. All 4 of matrix worked fine initially during burn in testing however 2 of the panels started to suffer many failed pixels after a few hours, usually blue or failure to pass data. All failures were on the 2 panels from the same supplier. The other 2 panels were perfect after full burn in.
    We decided to bite the bullet and replace all the pixels on the 2 dodgy panels that were failing and purchased another 2500 5v pixels, this time from Ray Wu as he appears to be respected on here and we did not want another dodgy batch.

    After replacing all 990 5v pixels on the first matrix panels I am getting terrible flicker on it. Test set up is F16v3 1 output direct to matrix pixel 1 via 60cm data cable. 60amp PSU for matrix. 6x 10 amp fuses. Power injected every 66 pixels. F16v3 powered from separate PSU (only data and ground taken from F16v3). 0v common for both PSUs. All data and 0v runs together and are of equal length.

    The flicker ONLY happens at low brightness with a steady single any colour but not the whole string flickers. It starts at around 300 pixels in but it is not consistent point where it starts) into the string and manifest as a bright flash of the same colour for the entire rest of the string. the flash gets brighter the further into the string and the rest of the string flashes together. At anything over 60-70% brightness there is no flicker at all. Full white at 100% is rock solid white, no flicker, no pinking. Sequences will play but high brightness flicker is still noticeable.

    Things I have tried to fix it (in no particular order).
    - Power injecting every 33 pixels -no change. (I've measured the wire cross sectional area of the Ray Wu pixels and they are pretty poor - 5 strands of 0.15mm diameter ~ 30-31 AWG).
    - power injecting every 22 pixels - no change. (All joints soldered and heatshrunk with glue lined heatshrink).
    - Replaced the first 495 pixels (half a panel) - no change.
    - Tried another controller (cheap Ebay ws2811 pre-programmed thing i use for testing) - only drove the first 305 pixels but the flashing started earlier (around 150 pixels in) and was worse (more frequent and brighter flashes, sometimes different colours but always in sync together) over all.
    -Completely rewired all power injection 0v and 5v. - no change.
    - Measured resistance of each 0v and 5v 66 pixel section of the panel (after disconnecting all common power and zero feeds) - good continuity (<2.0 ohm per 66 pixel length). - no 0v breaks which is what I was testing for mainly.
    - Measured voltage drop at power injection points throughout the panel - 5.01v at source with no load. 5.01v at furthest pixel from injection with no load. At 100% brightness, all 995 pixels on white - 4.89v at worst point.
    - Reduced string length to 500 pixels (half panel) - no change.
    Swapping back to one of my original (Ebay supplier) pixel matrix results in perfect operation).


    Out of desperation, set up a complete test rig on lounge floor:
    - Laid out 10 x 50 pixel strings (brand new out of the bag from Ray Wu).
    - Set up power injection to the bare wires at the start of each string (different 5v 60 amp PSU).
    - Set up F16v3 direct to first pixel string.
    - added 50 pixels strings one by one whilst F16v3 set to around 10% brightness, solid red. (worst case for flicker).



    Up to 5 strings (250 pixels) - no flicker at all under any conditions.
    6th string added - some flicker on 6th string only.
    adding more strings results in flicker on additional strings. The flicker/flashing brightness tends to move to be most bright towards the last few strings only.
    With all 10 strings, flashing starts around 300 pixels (same as matrix).
    Never flicker or flashing on first 250 pixels, even when remainder of string is flashing.
    Tried:
    - adding an f-amp in between F16v3 and first pixel - no change.
    - adding an f-amp in between every 50 pixels (one by one) - no change.
    - adding 220 ohm resistor between F16v3 and first pixel data - no change.
    - adding 220 ohm resistor between each 50 strands data - (one by one) - no change.
    - Adding a single split choke around various wires at many points (one by one) - no change. (only had one choke of unknown value).
    - programmed a sequence to have pixel 0 to 250 pixels permanently off and pixels 251 to 295 to ramp up and down solid red slowly - flashing on whole of the second half (251-495) at low brightness - exactly the same as if the first half was on as well.
    - disconnecting the data-in at the first pixel when set on a low brightness, causes all flickering to stop.
    (All 10x 50 pixel strands work on their own or in any combination up to 250 pixels all the time).

    All data is run with equal 0v runs but I am pretty sure it is a data corruption problem and not a power injection problem. There must be something different between the Ray Wu pixels and the Ebay ones. The Ebay pixel chips are marked "WS2811" and the Ray Wu ones are marked "WS2811s" but I cant find any technical specification differences for the "S" variant on the various tech sheets I've looked at.

    We built many different props for the first year using nearly 7000 pixels in total and runs of up to 1000 5v pixels in one string on a single output of the F16v3 with no problems whatsoever, but this latest batch of Ray Wu pixels is causing me endless weeks of headaches - Please help if you can.

    Many thanks in advance.
    Steve.
    Last edited by pixel-newbie; 06-13-2020 at 05:48 PM.

  2. #2
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    Default Re: WS2811 flicker but only at low brightness - Help please?

    A lot of times, it’s operator error. I say that by way of experience and hoping it gives you comfort. Like me spending hours trying to get some P5 panels working yesterday, then realizing I was powering the octoscroller off a wall wart instead of the PSU powering the panels.

    Did you solder your own connectors between the pixel strings? Often a small short between data and V+ or ground can cause that kind of artifact. It could be as simple as having a tiny solder spike poking through the shrink tubing. I’ve had that happen a number of times.

    And are you 100% sure you have 5V pixels?

    Have you switched outputs on the F16v3 and repeated the test?

    Have you checked the F16v3 settings and made sure you have defined the outputs correctly?

    Have you changed out power supplies?

  3. #3
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    Default Re: WS2811 flicker but only at low brightness - Help please?

    you said sata, you did not mention data plus v-. always make sure both wires run together. noy doing this causes lots of odd side effects.


    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

  4. #4
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    Default Re: WS2811 flicker but only at low brightness - Help please?

    Thanks for the suggestions.

    Yes, all connections on the matrix are soldered and heatshrinked. (On the lounge floor test, I just used the small connectors that came on the strings and screw terminals for power injection as it was just a quick test) - both set-ups behaved identically. There is the possibility of a solder spike shorting through the heatshrink on the matrix, but I do always check for sharp solder before shrinking, we have re-made the entire wiring several times, and the same behavior is present on the lounge floor test with no soldering, so I am pretty sure it's not a solder spike short.

    We have switched outputs on the F16v3 - no difference to the flickering (and the same outputs drive the original matrix (identical build style) with no issues.
    F16v3 is set for WS281x output and channel counts correct - are there other settings I should be looking at (bearing in mind the exact same F16v3 channel drives all my other pixels with no issues, including an identical matrix panel that shows no issues). I did think it could be timing tolerance thing but couldn't see any other settings in F16v3 or FPP to adjust.

    We have ensured all data and 0v runs together, and are equal lengths.

    I have tried two different PSUs (but they are the same model/style)- no difference (and both PSUs do power my original matrix without issues). I will check in the store for a completely different model/manufacturer PSU and run tests again today.

    The 5v pixel question is interesting - I dont know is the answer. I ordered 5v from Ray Wu and the invoice states 5v, so just assumed they were.
    I have pulled all the resin of one of the spare pixels: There are no markings on the board other than "WS2811" on one side and the chip has "WorldSemi WS2811S 20191107" on it. The only components on the pixel board are the chip and the led. Should I expect some resistors if the pixels are 12v?
    How would I check what voltage pixels I have for sure?

    Many thanks again for any help,
    Steve

  5. #5
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    Default Re: WS2811 flicker but only at low brightness - Help please?

    UPDATE:

    So following Kensington's question of have I got 5v pixels, I started examining the pixels from Ray Wu (that have the issue) and a selection of my older pixels that do not exhibit the issue to look for differences.

    After pulling the resin off a Ray Wu pixel, the only thing on the board are the chip and the led. All my other pixels have two surface mount components between the chip and where the wires are soldered. it looks like one is a resistor (marked 101) and one might be a capacitor. It's really difficult to see where they are connected with the remaining resin. pictures attached.

    The Ray Wu pixels are missing these two components - Could that be the cause of all my problems ?



    So we set up 10x 50 strings from Ray Wu again and made up a load of single pixels with pigtails from the old stock (with the surface mount components) to insert between each string of Ray Wu pixels. It did improved things somewhat. The flashing was only on the last couple of strings of 50 with less flashing/flickering this time but still unusable as a string of 500 pixels . (Tried with an old pixel at the very end as well, but it made no difference). Unfortunately, the matrix use 995, so still not a solution.

    I am now pretty convinced there is something wrong/different with the 2500 Ray Wu pixels I have.
    What do people think about the missing resistor and capacitor ? Should I contact Ray Wu? Any ideas for an external to the pixel resin fixe I could try to fix/improve it.

    thanks again,
    Steve
    Attached Images Attached Images

  6. #6
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    Default Re: WS2811 flicker but only at low brightness - Help please?

    WS2811 is followed by a package type ID. In this case the 'S' means SOP-8. All of the reference designs indicate there should be three resistors and one capacitor. One of the resistors can be left out (the one on the DI line) but the rest should be there.


    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

  7. #7
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    Default Re: WS2811 flicker but only at low brightness - Help please?

    Here’s the reference document Martin mentioned. It gives the resistor values and their placement. You could try manually rigging some resistors right before the flickering pixels and see if that changes anything.

  8. #8
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    Default Re: WS2811 flicker but only at low brightness - Help please?

    Hi, on the newer boards the 100R resistor and the 0.1uF capacitor are on the other end of the board.

    https://www.alibaba.com/product-deta...7c4e79cd5fTsHz

    Just for reference the link in post #7 is to the old data sheet. On the first page bullet point 3 states:

    “Gray level 256 can be adjusted and scan frequency not less than 400Hz/s.”


    The new data sheet the same bullet point reads:

    “256 Gray-scale adjustable and scan frequency is more than 2KHz.”

    There are other changes but that for me is the easiest to tell the difference. It can be downloaded from the world-semi web site.


    But to your issue. The newer pixels have a different 'RESET' time and new firmware has been issued by most pixel controller manufacturers to accomadate this, have you updated your controller?
    Last edited by Barnabybear; 06-14-2020 at 05:19 PM.

  9. #9
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    Default Re: WS2811 flicker but only at low brightness - Help please?

    Thank you again.
    I've tried to scrape the resin off a bit more to get a better picture showing the location on the other end of the board -Slightly better picture attached. The picture's not great but the resistor and capacitor are definitely not on the board at either end. What would your advice be regarding missing resistor/capacitor please?

    I will admit I have never updated the F16v3. It was purchased around Feb 2019 but didn't get it into the UK until around Sep 2019 - it worked so i didn't want to make changes just as I was getting the 2019 Christmas show ready (steep learning for those few months). I will get it out again tomorrow and check which firmware I have and check for an update. Are you able to run old and new timing pixels on the same F16v3?

    I'm hoping it's a firmware timing issue - fingers crossed, but fearing I have 2500 pixels with missing resistors and capacitors!

    Thanks again.
    Attached Images Attached Images

  10. #10
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    Default Re: WS2811 flicker but only at low brightness - Help please?

    the inter frame gap was extended over four years ago. it would always cause the first pixel to not function properly (and any pixels after it). After 10 pixels from the controller this timing change will not matter.


    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

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