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I have an Arduino Nano connected via USB to a Mac Mini. When the LEDs come on, an external speaker connected to the Mini starts to hum/buzz quite loudly. If the LEDs are turned off, the buzz stops.

The speaker and the Mac mini are both powered independently, and are plugged into one wall socket, while the 5V power supply to the LEDs and the Nano is plugged into a different socket (of the same outlet).

What could be causing the buzz and what are the possible remedies?

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    WTH is a "fadecandy"? – Majenko Jul 20 '17 at 21:32
  • Changed to Arduino – Tom Auger Jul 20 '17 at 21:35
  • Post your sketch, please. What pin are you using for the LED? Are you using digitalWrite, analogWrite, tone ... ? – user31481 Jul 20 '17 at 21:48
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    make sure you run a common ground between the amp and source – dandavis Jul 23 '17 at 22:16
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    for a mac mini, you can use a chassis screw, for the 5v stuff you can use the negative rail. On a laptop to receiver setup i have going, I have an alligator clip biting a half-inserted USB plug's meta collar, the other jaw biting a lead from the FM antenna gnd on the back of the receiver. w/o, i get hum, occasional clicks, and pink noise, but as soon as the clip bites, near silence. Shielded cables helped a little, but the ground connection basically fixes the issue completely. – dandavis Jul 27 '17 at 20:05
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If this is the same project you described in this question(readers: "112 WS2811s in series" causing interference), your external speaker may not be filtered very well against energy radiated by nearby un-shielded wiring. Try a pair of headphones in place of the speaker - does it also buzz? If not, the speaker (system) is probably picking up the interference. If so, the pickup is probably within or near the Mac mini.

You could try a few simple solutions (or at least tests that might narrow the problem):

  • shielded audio cable from the Mac mini to the speaker;
  • shielding the speaker enclosure and grounding the shield;
  • shielding the connections to the LED string (obviously shielding the LED string itself is likely to be aesthetically undesirable);
  • separating the speaker from the LED strip by more distance;
  • powering the mini from batteries - at least long enough to learn whether the power wiring might be involved.
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  • It's not the same project, and I would like to believe the issues are not related (the other one has to do with voltage changes probably due to common power source). However your tests are very helpful. I have significantly upped the LED power supply (from 8A -> 30A) and am pluggin both power supplies into a big old UPS with shielded power and the buzz seems to have gone away. – Tom Auger Jul 27 '17 at 16:39

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