Three of my modules are picking up Arduino noise.

Hashtag Octothorpe · Joined: Jun 11, 2017 Posts: 57 Location: Grand Rapids MI

I have three modules that pick up noise from a couple of my Arduino modules. Both of the noisy Arduinos drive addressable RGB LEDs and one of them drives a four-digit 7 segment numeric display. When the display is showing "b120" for example (120bpm) I get more noise from these three modules than when it's showing "1 3" (channel one is doing 16th notes)...

Aaanyway, it seems to be high frequency switching of the serial data streams that's creating audio interference.

The three modules that are picking up noise are: my two TB-303 clone low pass diode ladder VCFs that use transistors (unmatched because who has the time) for the output stages, and only one of my three MS-20 clone low pass VCFs (but only when it's fully closed down and then the noise pops in after half a second). Those three modules aren't near the Arduinos physically or electrically... the bus for ground and power run up the middle of my synth and the modules are on the left and right side.

I don't have ferrite beads on the power feeds to any of these modules but I rarely do because usually it's not a problem. I do religiously bypass all my ICs with ceramic disc 104 caps like you're supposed to, because I exploded a bunch of expensive LM3886 power amp chips because I didn't understand bypassing.

ixtern · Joined: Jun 25, 2018 Posts: 145 Location: Poland

cslammy

PHOBoS · Posted: Wed Jan 23, 2019 9:31 am Post subject:

I have noticed that for circuits using a microprocessor those ferrite beads can actually make a lot of difference. (I usually don't use them either)
Dedicated supplies is also a good idea.

Hashtag Octothorpe · Joined: Jun 11, 2017 Posts: 57 Location: Grand Rapids MI

I put ferrite beads on one of the noisy Arduinos and it didn't make any difference. I found one particular circuit that was picking up most of the noise (a TB-303 ladder filter) and also beaded that, AND put 2,500uFs of capacitance across the filter's power rails, in addition to the 100nF ceramic disk, and that made the noise a bit quieter... but still very much there.

So I'm now seeking how to make the filter circuitry itself quieter.

Grumble · Posted: Sun Jan 27, 2019 3:32 pm Post subject:

my guess is that not the arduinos are causing the noise but the current thru the leds is.
so you could try to decrease the steepness of the currents thru the leds or have this current sourced by a dedicated power supply (and don’t forget the return path for the current! )