How to suppress terrible noise from MAX7219?

Discussion in 'The Projects Forum' started by pashkatarakashka, Dec 22, 2012.

  1. pashkatarakashka

    Thread Starter New Member

    Dec 22, 2012
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    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. http://www.youtube.com/watch?v=5XsQk7azH2M&feature=youtu.be
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    I do not see a MAX7219 in your schematic. What gives? If the problem goes away on batteries, then the problem is most likely in the power supply and not the chip. Also where are your bypass capacitors?
     
  3. tubeguy

    Well-Known Member

    Nov 3, 2012
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  4. John P

    AAC Fanatic!

    Oct 14, 2008
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    You've chosen to do something that really isn't recommended, putting digital components and sensitive analog components on the same power supply. I suspect that any improvement you can make will just be incremental.

    It could be worth a try to put an inductor in series with the power supply to the MAX7219. Have plenty of capacitance, say a few hundred uF, near the Maxim chips and as Tubeguy said, have ceramic caps as close to the chips as you can. I'd try to make the inductor at least a few hundred uH. You need to evaluate its resistance along with the maximum total current the LEDs will be getting, to be sure the voltage drop isn't too bad.

    Also, your wiring is horrible. At least twist together the power and ground wires going to the LED module.

    Does this device have a higher-voltage incoming power supply feeding a 5V regulator? If so, split the incoming power line and install two regulators, one each for analog and digital. That might help.
     
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