How to suppress terrible noise from MAX7219?

[pashkatarakashka]

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.

 

[crutschow]

Put your 220μF cap and a 0.1μF cap directly from the power pins to ground pins on the MAX7219. The fact that a battery eliminates the noise indicates that you have a power supply problem.

What amplifier is generating the noise?

Your breadboard is such a kludge of wires, the problem could be anywhere. A good place to start would be to shorten all wires to the minimum length required to make the needed connections. Also run separate power and ground wires from the MAX7219 and the amplifier to the power supply. And there should be decoupling capacitors across all ICs from power to ground.

 

[audioguru]

That is the second messy tangle of wires that has been posted this morning. I hope there will not be more.

The LM386 has pin7 that is for a filter capacitor to ground. Try 10uF.

 

[jbeng]

In addition to your other noise mitigation solutions, you might try using the MAX7221. It functions basically the same as the MAX7219, except that it's outputs are slew-rate limited to reduce the amount of EMI the chip generates.

 

[dr pepper]

Dont worry about the mess of wires, my prototypes are just as bad.

If you have another breadboard build your audio circuit on that with a big cap paralled with a 0.1uf accross the supply.

The noise may also get in on the i/p of the amp too, so you might need to reduce the noise at source, maybe build the display on a piece of veroboard and use a cap/resistor filter to power it.

 

[atferrari]

My very first project including a micro involved a MAX7219 as well. Worked quite well and I do not recall any horrible noise much less from that IC in particular.

Maybe your layout is not helping.

 

[audioguru]

Multiplexing the LED display by the MAX7219 causes the power supply voltage to jump up and down.
The power supply noise is amplified by the LM386 amplifier because it is missing a filter capacitor to ground at pin 7.

 

[pashkatarakashka]

I'm preparing PCB and will post full schematics/pcb with recommendations in case the problem is not solved.
thanks

 

[dr pepper]

Make sure on the pcb that you have a good meaty ground with thick tracks to every part on the dispaly, well the whole board for that matter, use the fill command for any sections of the board unused and connect it to ground, and make sure the full outer of the pcb has a continuous ground track.
Might also be worth making provision to disconnect the audio amp from ground using a link in case you want to connect it somewhere else to test.