Teensy 4.0 and OctoWS2811: strange flickering behavior with some LEDs

M

MountainView

Member
I have a Teensy 4.0 connected to an OctoWS2811 adapter that I plan to use to drive some LEDs. I loaded the BasicTest_RGBW program and plugged it into a strand of WS2812B LEDs. It appeared to work fine, displaying pixels in six different colors (and some unlit pixels) that change every couple seconds. Then I tried plugging it into a different strand of WS2812Bs and it displayed chaotic, rapidly strobing colors. The pixels mostly appeared white but sometimes flashes of other color would strobe in. The pixels would change dozens of times a second instead of once every two seconds. I plugged in another strand of bullet-style 5V WS2811B LEDs and I saw the same chaotic strobing.

These lights are all supposed to be compatible, in the case of the first two strands they are the same type of LEDs. Do you know what could be going wrong here? Are there some refresh rates that cause this problem with some lights? Thanks for any advice. If needed I can take video of this but the difference is so dramatic the description alone may be enough to indicate the cause.
 
Lower quality LED strips might have less adequate decoupling? Or have counterfeit chips?
 
I suppose, one of the LED strips with the problem was from Alitove, probably this one:

alitove.com

LED Strip Lights | LED Lighting Strip | ALITOVE

Discover LED strip lights at ALITOVE, Illuminate any space with our versatile LED lighting strips, designed to add brilliance and ambiance to your home, or outdoor area.
alitove.com alitove.com

Is Alitove a trustworthy brand? Has anyone else used them with a Teensy? I had them work fine when they were connected to this controller:


How might the output of the Teensy differ from what this controller sends? Both problem strands were acquired as surplus from other projects so I don't know their specific models and specs. The fact that they have the same problem makes me wonder what could be up.
 
What is your drive voltage on the data signal into the LEDs?

Going from memory here but the datasheet requirement for a valid high input is 0.8*Vcc so 4V. The Teensy IO pin high voltage is just under 3.3V.

The LEDs will normally work with voltage below the datasheet requirement but how far below will depend on the LED which means you will get some that work with a 3.3V input and some that don't.
For reliable operation you really should buffer the output signal and bring it up to over 4V.
 
The OctoWS2811 Adaptor uses a 74HCT buffer so its 3 volt compatible - so long as Vin is 5V you should be good. Unless the LEDs overload your supply perhaps?
 
Have you checked the ground connections? That can also cause such problems, when the ground from the LEDs is not connected to the Teensy / Otco... ground.
 
Have you definitely got RGBW strips or are they RGB? If you use the wrong demo code the extra Byte per pixel could cause some crazy behaviour.

Otherwise, agree with having a good common ground between Octo Board and always worth putting a capacitor across the VCC and GND lines at the strip to help suppress and huge demands in current.
 
Thanks for the tips, I thought that the OctoWS2811 buffers the output signal but does it need something extra to produce a 5V data signal? I haven't connected anything from the strip to the Teensy or Octo grounds, I have a power supply (Meanwell NES-100-5) that the grounds are connected to. I'll try adapting the code to RGB.
 
MountainView said:
Thanks for the tips, I thought that the OctoWS2811 buffers the output signal but does it need something extra to produce a 5V data signal? I haven't connected anything from the strip to the Teensy or Octo grounds, I have a power supply (Meanwell NES-100-5) that the grounds are connected to. I'll try adapting the code to RGB.
Click to expand...
If there is only one power supply which powers both the Teensy and the LEDs there is only one ground which has to be connected to all parts.

In the case of powering the Teensy from another source (USB, powerbank, another power suplly) it is important that all grounds are connected.

It was already mentioned that the OctoWS2811 has a 5V input. If everything is connected as intended (ground and 5V), it should give 5V data output which should work very likely also for older chips or more sensitive to exact levels on the data signal. As said, current WS2812(B) LED strips usually work directly with 3.3V.
 
MountainView said:
Thanks for the tips, I thought that the OctoWS2811 buffers the output signal but does it need something extra to produce a 5V data signal? I haven't connected anything from the strip to the Teensy or Octo grounds, I have a power supply (Meanwell NES-100-5) that the grounds are connected to. I'll try adapting the code to RGB.
Click to expand...
I should have been clearer, the 74HCT245 buffer in the OctoWS2811 is a 5V part with 5V outputs, but its inputs are guaranteed to work with 3V inputs. That's what the 74HCT family is good for (originally it allowed interfacing TTL to CMOS, but they are usually used these days for 3V compatilibity).
 
TomChiron said:
If there is only one power supply which powers both the Teensy and the LEDs there is only one ground which has to be connected to all parts.

In the case of powering the Teensy from another source (USB, powerbank, another power suplly) it is important that all grounds are connected.

It was already mentioned that the OctoWS2811 has a 5V input. If everything is connected as intended (ground and 5V), it should give 5V data output which should work very likely also for older chips or more sensitive to exact levels on the data signal. As said, current WS2812(B) LED strips usually work directly with 3.3V.
Click to expand...
Thanks, it's starting to make more sense. My setup has involved the Teensy powered by USB and connected to the data pin of the LED strand, whereas the strand's power and ground are connected to the 5V power supply. Therefore I should connect the OctoWS2811's ground to the power supply, correct? Would the best way be to install a screw terminal block on the OctoWS2811 adapter as seen in this photo (https://www.pjrc.com/store/octo28_apa102.jpg)?
 
It is possible to connect the ground at the adapter, yes.

In large setups, often I find it practical to have the ground connection (from Teensy/adapter to the LED power supply) at the LED strip. There is a ground on the output jack of the Octo adapter for each data line.

Edit: this way it is easier with long cables and the power supply or several of it for the LEDs can be far away from the Teensy, from where only the data lines with ground goes to the LEDs...
 
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