Hi guys!
I have a ws2812B strip, and i cant make it work.
I tried it with an arduino uno and also with a teensy 3.6, but its not working.
Check the video please, i used FirstLight example in it.
I do the wiring correctly, grounds are together, so i dont know whats happening here.
I tried to use FASTLED_ALLOW_INTERRUPS 1 and FASTLED_INTTERUPT_RETRY_COUNT 1, but it doesnt helped.
Sorry for my bad english and thanks for the help! 
video 1582221636 - YouTube
Show us a good schematic of your circuit.
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I would start by getting the Arduino cookbook and reading it. Also on line there are many videos etc showing the Arduino and how to do what you want. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil