Public Service Notice
There are multiple versions of the WS2812B programmable LEDs.
But if you google for “WS2812B datasheet”, this one from Adafruit is the top ranked result. That’s the old one.
The old one requires an idle time (“reset”) of 50us or more. On the new one, that has been increased to 280us. That makes them backwards incompatible…
Guess which one I had been developing for first, and what happened when I connected a different LED board?
You can distinguish old and new by the pattern inside the LED eye:
The complete timing tables:
This blog post goes into more detail about difference between the old and the new version.