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Large LED project partially flickering
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Large LED project partially flickering

by Chad_gnet on Tue Feb 12, 2019 9:58 pm

Hello!
This is my first post here; please let me know if I need to provide more information, less information, etc.

tl;dr Displaying dim colors on a large LED setup causes excessive flickering. Bright colors still flicker, but it's much less visible.


The Setup:
We have a 2,476 LED display that we're hanging in the foyer of our company's office. There is a metal ring 12 ft in diameter with a wire mesh (like a tennis racket). The LEDs are attached at each junction, about 3 inches apart. See attached image "LEDs.jpg". The labels are to give reference points to the other photo.
A Raspberry Pi 3 Model B runs the whole show. It has 7 FadeCandys plugged into it via 3 onboard ports and a 4-port USB hub plugged into the final port. The FadeCandy channels each have 50 WS2811 5v LEDs attached, purchased in pre-strung links. Crimp joiners are used at the ends of runs where it's too far to reach the next row. 2 Mean Well RSP-320-5CC 300W 5V power supplies provide the juice. All power and data wires are 18 gauge.
The Pi, FadeCandys, and power supplies are all in the wooden box at the top of the picture. There are two 80mm fans in one of the sides to provide airflow.

The Problem:
The bottom half (anything below the red line in the pictures) has a noticeable flicker when displaying dim colors. See "Flicker - Still.PNG" for a mid-flicker still taken from a video I have of the issue.
The GRB value I'm using to test is (16,128,16). When (0,0,0) is sent, there are brief "pops" of color in the LEDs in the lower half. Our logo is two bright colors, GRB (10,10,255) and (244,245,255). When displaying that, the flicker is barely noticeable; you have to know where to look and stare hard.
My thought is some sort of interference on the line that causes more issues when low-voltage signals are being sent. My understanding of how the data line works is a low voltage is sent to drive dim colors, and higher voltages drive the LEDs brighter.

Attempted Solutions So Far:
  • Before we built this, we tested with data lines 12 feet long, and we were able to set colors correctly. It's been a long time since we were at the "proving" stage, but I don't recall any flickering.
  • Confirmed that the ground for each LED string and the FadeCandy driving the LED string returns to the same power supply.
  • Added a surge protector/line filter between the building's power and the Setup. The Pi and both power supplies are plugged in to a power strip, which is then plugged in to the surge protector/line filter.
  • Turned off as many power breakers as possible to eliminate outside interference while still powering the Setup.
  • Changed the data wire to one of the problematic lines.
  • Changing which FadeCandys drive which area - switching one from driving the "upper" section to the "lower" section. The flickering stayed in the same spot, suggesting it's not the FadeCandy causing the issue.
  • Tried to separate a couple data lines from the bundle of wires you can see to the left of the box. That line still flickered.

We pushed to get the logo displaying before a company anniversary party late last year. It just needed to display the bright colors of our logo, so that was fine. Now we want to display any given color without flickering. We're also going through a clean-up phase so we don't have a rat's nest of wires like what's in the photo.

My current thought is the data line is too long, but it worked when we tested those lengths. Also, it's failing as quickly as 6 feet from the source, and the flickering does not get strictly worse as you go - the worst of it is at about 75% of the way down. The LEDs at the far end perform better than those at 75%


Any advice to reduce the flickering as we go through this "tune-up" phase would be greatly appreciated!

Warm Regards,
Chad

P.S. I have a video of the flickering, is it possible to post that? If I convert to a gif, can I post it?
Attachments
Flicker - Still.PNG
View from below the ring, LEDs on, mid-flicker
Flicker - Still.PNG (526.51 KiB) Viewed 74 times
LEDs.jpg
View from above the ring
LEDs.jpg (906.52 KiB) Viewed 74 times

Chad_gnet
 
Posts: 2
Joined: Tue Feb 12, 2019 7:50 pm

Re: Large LED project partially flickering

by adafruit_support_bill on Wed Feb 13, 2019 7:13 am

My thought is some sort of interference on the line that causes more issues when low-voltage signals are being sent. My understanding of how the data line works is a low voltage is sent to drive dim colors, and higher voltages drive the LEDs brighter.

WS2811s are controlled digitally. The data line is a continuous stream of 1's (5v) and 0's (0V). At higher intensities there will be more 1's on the line. At lower intensities, there will be more 0's.

One possibility is that you are getting some interference between the strands due to the PWM switching noise of the pixels.. One thing to try as an experiment is to separate one of the strands from the array. Keep it all connected, but detach it from the grid and separate it from the adjacent strands and see if the flickering on that strand goes away.

adafruit_support_bill
 
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Joined: Sat Feb 07, 2009 10:11 am

Re: Large LED project partially flickering

by Chad_gnet on Tue Feb 26, 2019 12:40 pm

Hello! Thank you for your quick response, and I apologize for the delay in mine. We have been working on the mounting (replacing ropes and tie-offs with cables and winches), so I have not had a chance to test this. I will likely be doing that in the next couple of weeks, and I'll let you know what we find!

Best Regards,
Chad

Chad_gnet
 
Posts: 2
Joined: Tue Feb 12, 2019 7:50 pm

Please be positive and constructive with your questions and comments.