NeoPixel RGB Neon-like on Raspberry Pi 3B+ won't light up

[jwinslade]

When I had the issue on the Pi 3, it was with a new NeoPixel array, and I sanity checked it by feeding in to the array data in some variable duty cycle square waves from a function generator (at 800 kHz, IIRC) and I did get the array to light that way. I then tried it with the RPI 2040 Feather and it worked as expected.

I thought of scoping the RPI data output to see what was actually going on, but have not.

Anyway, it's good to know that they will work on the Pi 3 without the desktop.

Thanks.

[OleTR]

This is for a work project and not for hobby. As we have several systems and software built upon the Raspberry Pi, I can't simply change the hardware.

Thank you for testing it and various Pi versions and scenarios.

Yesterday evening I was digging around if there are any other libraries available and came across some crucial information.
According to this source (Preparation & Installation) and some other websites I've visited it seems that you need to disable audio on the Raspberry Pi or else it will mess up the timings.
I just did that and both neopixel stripes are working. This would also explain why the non-desktop versions are working, they probably have audio disabled by default.
This is some crucial information and I'm kind of disappointed that it's not in any of the guides from adafruit. In my opinion this should be included.

Thank you all for your help.

[danhalbert]

@OleTR Thank you for finding that reference. We will find a place to put a warning in the guides about audio. I think most of our testing was done on headless systems.

[jwinslade]

My guess is that it was developed on the Pi without the desktop, just using it as a controller.

I have the Pi Top which has the Pi 3, and when I get some time I'm going to try it on that, disabling the sound (the Pi Top does not have speakers) and verify if that's the trick. It does make sense.

[adafruit2]

the pwm peripheral we use for neopixels are used for audio on the headphone jack. if you switch to hdmi audio that will free the pwm peripheral. or you can try using the SPI peripheral, i think thats gpio 10
see
https://github.com/jgarff/rpi_ws281x
for deets

[OleTR]

Well in this occasion I won't need audio, but it's still good to know, thank you for the further informaiton.