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I have a WS2812b addressable RGB led ribbon that is 5m (150 RGB leds). I purchased a 5v 10amp power supply to power it; however, whenever I try to use it to power the LED strip the leds start flashing colors like crazy. Is there a reason I would be seeing this behavior or is this a sign of a bad power supply?

The setup is very simple, the data line is coming from an Arduino Uno, the voltage and ground are from the power supply. The program is just one of the sample ones with FastLED library and works "fine" when just powered by the arudino's 5V pin.

Thank you

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    Are the ground of the power supply and of the Uno connected?
    – chrisl
    Sep 5, 2020 at 21:45
  • No, the Arduino is powered by a separate source and no grounds are shared. Would that cause the issue?
    – Phillip Clontz
    Sep 5, 2020 at 21:52
  • 1
    That seems to have fixed it. Thank you!
    – Phillip Clontz
    Sep 5, 2020 at 22:02

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The strip and the Arduino need to share the same ground connection. They are communicating through voltage and voltage is always a difference between two points. The power supply sets the supply voltage as the difference between + and ground. The chips in the strip will then try to measure the voltage on the data line relative to their ground. When the grounds are not connected, the Arduinos output pin is floating somewhere else, depending on external factors. By connecting the grounds, both devices (Arduino and strip) use the same ground value to measure voltages. Only this enables communication between the devices.

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