SK6812 RGBW unstable

Hi, I’ve recently bought some strings of RGBW SK6812 modules. They work alright in solid mode, no flickering, brightness is alright, colours match but when fading or when an effect is running they erupt into a rainbowy mess. Not necessarily flickering, more like stepping. Subjectively it -feels- like a timing issue. White channel calculation modes make no difference.

checklist:

  • grounds are tied (common 5VDC PSU for both ESP and string)
  • short (10cm) signal lead
  • V0.11.1 prebuilt binary for ESP8266

Anyone else had this issue? Am I noobishly missing something?

Thanks for any pointers!

amended checklist:

  • issue is independent of power supply
  • same with a different string (same supplier and type, different piece)

Correction: it seems to be linked to the white channel after all. With white channel disabled and the white slider fully down, effects work alright, the flickering starts when a dash of white channel is added in.

If it starts when white added in I would be inclined to say check your power. Adding the white will draw more current.
If you don’t see a power problem then I am uncertain where to go.

Power is software-limited to 75% of PSU capacity and the issue is reproducible on two different lab bench PSUs (both switched-mode and linear), a USB phone charger and a random 5VDC power brick.

How many leds do you have? And do you power inject

50 LEDs spread across 5m of what looks to be .22mm stranded cable, powered from both ends. Issue happens even at very low overall brightness settings. I consider power issues effectively ruled out.

One more question I just thought about. Are all the grounds tied together? Sometimes a loose or missing ground could cause this. It would probably show more on patterns vs solid.

Indeed they are, there is a single common PSU for both ends of the string and the ESP.

Thought I would ask. Not sure what to say at this point. All I could offer is try different wire for the connections. Maybe a larger gauge. I had some wire cause me a problem once, could not believe it.

Both ends power might be part of the problem due to ground loop.

Try to power the strip on one end with GND and signal and on the other end with +5V alone.

Measure the remaining voltage on one end and compensate on your PSU to get 5V. You will not overdrive your strip, by doing that, you just compensate the ohmic loss.

Such a configuration is better for long strips and guarantee that all the leds have the same voltage and current through, if both lines have the same resistance.

Don’t forget that expected signal is 5V and not 3V3…The simplest trick is to power a first led separately with a diode in serie and get an acceptable level shifter.

Let us know…

Hey!
I’m having the same problem. Al colors work well, but when you use the colorwheel and pull it towards the middle the leds begin to change colors randomly.
I added a levelshifter (SN74AHCT125N) but that didn’t solve the issue. I also tried a different ESP pin. I’ve made a video (https://photos.app.goo.gl/jxDVkxVH5vnnUgJw7) to show the effect.

Oh cheers that is exactly the issue (and it also looks like we’re using the same style of string, soft ribbon cable and 5050 packages on small individual PCBs).

btw were the nice bulb-shaped diffusers a part of the string or have you added them later on? Could you share a link please?

I’ve hotglued them later on, I ripped those of a battery powered led string.

Led string with bulbs: https://a.aliexpress.com/_v1Ahm7
SK6812: https://a.aliexpress.com/_uIBwmn

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I stumbled across this topic: ESP32 + SN74AHCT125N, Wiring? Max. length data cable to SK6812? - #5 by Mekanikless
I tried adding several types of resistors between the level shifter and the ledstrip, but that doesn’t make much of a difference for me. I’ve ordered a oscilloscope to find out what exactly causes the problem, so I’ll be waiting for that to arrive.

If you cut the brightness by 50% and drag the colorwheel to the middle, does it still have the color shifting problem?

Yes, the first 15 or so LEDs are shifting colors and the rest are not in the correct color.

The original topic creator had 50 LEDs spread evenly along a 5m strip, power fed into both ends of the strip, and had the power supply common properly bonded to controller and strip.

What sort of similar arrangement do you have?

If you tell WLED you only have 15 LEDs, do the problem go away, or does it persist?

Does it happen when using a web interface or a smartphone app or both?

Does it only happen with non-primary colors? Meaning, is it always ok when displaying just red, just green, or just blue? Or does it only happen when some combination of colors are to be displayed?

What sort of similar arrangement do you have?
I have 50 leds with wires between them, presoldered. The total length is longer than 5 meters, I guess around 8 meters. I’ve connected the power only to the beginning of the strip with the same powersupply used for the ESP and the LED strip (same ground).

If you tell WLED you only have 15 LEDs, do the problem go away, or does it persist?
The problem persists.

Does it happen when using a web interface or a smartphone app or both?
Tried it, and happens on both.

Does it only happen with non-primary colors? Meaning, is it always ok when displaying just red, just green, or just blue? Or does it only happen when some combination of colors are to be displayed?
It happens only when the leds are dimmed with more than two colors. So orange (red and green) works while being dimmed, and full white (red, green, and blue) on full brightness also works. When mixing more than two colors (for example, red, green and white) and dimming the leds the flickering starts.

Just ran into this with a number of SK6812 RGBW strings I have. These are all pre-soldered with 10cm of wire between the LED’s. They are simply bare 1cm PCB’s with a SK6812 on board and soldered together with 3 wires in and out.

Works great on 100% master and segment brightness. If I tune down the master or segment (or both) brightness then trying to set more than any 2 of the RGBW sliders to other than 100% or 0% it causes the strip to flicker and flash.

I have done this with as little as 10 LED’s assigned to a segment and it doesn’t matter if it’s the 1st, middle or last 10. I can achieve the brightness I want by leaving the master and segment at 100% and simply dialing in the effective brightness with the RGBW sliders and that seems to work OK.

My power supply is a 5V5A and wired directly to the ESP32 and the strip, injected at both ends. Worst case measured voltage was better than 4.8 volts on the strip and 5.0 at the ESP32. Distance from the ESP32 to the string is 4cm.

I verified this on a SP511E device (latest firmware) as well as release 0.12 and 0.13b2 on an ESP32.
Further evidence that this is a software incompatibility is that I also used the same ESP32 device on a 40 LED RGBW ring and a string of sealed epoxy SK6812’s “nodes” that are spaced at 10cm. Both those strings work exactly as expected and allow full brightness control from master and segment.

My rough guess is a quirky timing issue with the bare string LED’s.

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Hi all,

Just thought I’d register to leave my findings on this issue.
I had the same issue with these individual SK6812 PCB’s and was curious why they were not drawing the amount of current I was expecting either (when testing the setup on a bench PSU)
What I found after looking at the PCB is that there is a 75ohm resistor feeding the supply of the LED and the decoupling capacitor, you could measure the voltage after this resistor and see it fluctuating when using an effect.
If you take the resistor out and put a link in instead (a blob of solder in my case), it sorts out all the problems!
Attached are my findings, I hope it helps :slightly_smiling_face: