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 Forum index » DIY Hardware and Software » Arduino
Three of my modules are picking up Arduino noise.
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Hashtag Octothorpe



Joined: Jun 11, 2017
Posts: 40
Location: Grand Rapids MI

PostPosted: Sun Jan 20, 2019 11:20 pm    Post subject: Three of my modules are picking up Arduino noise. Reply with quote  Mark this post and the followings unread

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.
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ixtern



Joined: Jun 25, 2018
Posts: 57
Location: Poland

PostPosted: Mon Jan 21, 2019 3:39 am    Post subject: Re: Three of my modules are picking up Arduino noise. Reply with quote  Mark this post and the followings unread

Hashtag Octothorpe wrote:
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.

I noticed in my Arduino module driving LED matrix that there is an audible (in headphones) electric noise on some powers supplies (e.g. from USB) and on some is not. I also have not ferrite beads on the voltage lines (although I know I should). Good project always has good supply filters, like this one from Erica Synths, for example:


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cslammy



Joined: Apr 27, 2018
Posts: 108
Location: USA

PostPosted: Wed Jan 23, 2019 9:11 am    Post subject: Re: Three of my modules are picking up Arduino noise. Reply with quote  Mark this post and the followings unread

Hashtag Octothorpe wrote:
I have three modules that pick up noise from a couple of my Arduino modules..


Hashtag: what/how are you powering Arduino modules? From 12V? From 5V?

I don't know if this will help you any, but I have always tried to power my "digital" (Arduino mostly) and analog circuits from different supplies. Each has its own rails and its own path to ground.

This includes Arduino boards that have dedicated analog audio on them, like a DAC to op amp thing. I try not to mix that with purely analog, such as VCO's or VCFs.

So far I haven't had issues....so maybe dedicated power for the Arduino circuits is something you can experiment with.

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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Wed Jan 23, 2019 9:31 am    Post subject: Reply with quote  Mark this post and the followings unread

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.

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Hashtag Octothorpe



Joined: Jun 11, 2017
Posts: 40
Location: Grand Rapids MI

PostPosted: Sun Jan 27, 2019 3:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

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.
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Grumble



Joined: Nov 23, 2015
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PostPosted: Sun Jan 27, 2019 3:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

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! )

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