# How to suppress terrible noise from MAX7219?

On the same power supply I have connected MAX7219, which is producing terrible noise to amplifier so I can hear refreshing frequencies of MAX7219. If I hook up amplifier to battery power supply the noise is gone. I've also tried to connect 220uF electrolytic capacitor to power supply input of this board, which decreased the noise but not removed completely. Shutting down MAX7219 for a moment, eliminates the noise. Still I can hear it even from far distance. Amplifier board is on small PCB. MAX7219 is on breadboard connected to Arduino. All powered from Arduino.

I understand breadboard wiring may produce some noises, but this one is too loud. Unfortunately I don't have the scope to tell the noise spectrum, but MAX7219 update frequency from datasheet is 800Hz.

This video is to show the sadness of situation. [watch video]

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Found a recording of 800 Hz online, this seems to be a higher frequency. Possibly a higher harmonic? en.wikipedia.org/wiki/File:800Hz.ogg – Joe Baker Dec 23 '12 at 1:29
I don't see any MAX7219 in your schematic. – The Photon Dec 23 '12 at 1:58
When you added the 220 uF capacitor, did you add it to the Arduino, the amplifier board, or the MAX7219 board? – The Photon Dec 23 '12 at 1:59
From your video it sounds like inductor whine. Sounds like you need a bigger (higher) inductance value to lower the frequency of oscillation in the SMPS. I think, as @ThePhoton explained, critical detail is missing in your schematic. – DrFriedParts Dec 23 '12 at 2:40
@Pablo, Spent a minute or two reviewing your schematic. Overall it looks very good. It's a long shot for solving your problem, but you might consider using more tightly spaced values for the bypassing capacitors instead of 10 uF || 22 nF. I'd suggest 10 uF || 1 uF instead. See Murata's app note (pages 18-19) for discussion of the "antiresonance" problem, which can happen when parallel capacitors are more than about 1 decade apart: murata.com/products/catalog/pdf/c39e.pdf – The Photon Dec 26 '12 at 17:15