Hi, i know that it's a simple question but i wanna make it clear. :o
I tried to use 3 adafruit neopixel shields by one microcontroller(Arduino UNO).
However it doesn't work at all.
So my question is that am I doing just wrong? or it's certainly impossible to use three shields at one Arduino UNO.
"So my question is that am I doing just wrong? "
You are not giving us enough information.
Show us a good schematic of your circuit.
Show us a good image of your wiring.
Give links to components.
https://forum.arduino.cc/index.php?topic=519037.0 (https://forum.arduino.cc/index.php?topic=519037.0 )
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Attach your 'complete' sketch between code tags, use the </> icon in the posting menu.
[code]Paste your sketch here[/code]