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My project is a sound reactive LED display on an Arduino Nano. There are 112 WS2811s in series connected to 5v, Gnd and D5 via 220ohm resistor.

I have a Keyes style sound detection module that has an analog output. It is connected to 5v and Gnd as well, and to A0.

The code reads the analog signal and then maps it to the brightness of the LEDs, in theory causing the LEDs to pulse.

Unfortunately what's happening is the brighter the LEDs, the higher the readings on the analog pin from the sound module.

Power is 5v 3A connected directly to Gnd and 5V with a 1000mF cap across + & - on the barrel adapter. I did this to allow the LEDs to draw the full 3A from the AC/DC converter (and to avoid having to power this via USB)

My suspicion is that as the LEDs get brighter the voltage to the sound module fluctuates which is throwing off the readings. Is there some merit to this hypothesis or is there another possible explanation?

Short of running two separate power lines (one to the Arduino and the other exclusively to the LEDs) are there any other ways I can regulate the voltage to the sound module regardless of the draw by the LEDs?

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    Your suspicion sounds very likely. Temporarily running the Arduino and sound module off another source, with only a common signal ground shared with the LED supply, could be a way to test if that is related to the problem. – Chris Stratton Jun 13 '17 at 3:34
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    adding a schematic and your code would probably help the people trying to help you to give you better help. – Delta_G Jun 13 '17 at 3:54
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    Is not the Arduino Uno's barrel adapter connected to the Arduino Uno's linear 5 volt regulator. That regulator likely needs more than a 0 volt drop across it's input and output. Does your sound card sit on top of the Arduino leaching power from the Arduino board. Consider what the sound card would see if it is leaching power after the Arduino Uno's 5 volt regulator. This is where a schematic of your setup is needed. Because all we can do otherwise is guess as I have just done above. – st2000 Jun 13 '17 at 4:13
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    It's a Nano, not an Uno, so I've wired up my own adaptor as I mention in the OP. – Tom Auger Jun 13 '17 at 14:35

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