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How to suppress terrible noise from MAX7219? — Parallax Forums

How to suppress terrible noise from MAX7219?

yamadanaoyamadanao Posts: 2
in General Discussion
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.

Here is the date sheet of max7219


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.

kUbyk.png

Comments

  • hatallicahatallica Posts: 175
    My gut feel, based only on the supplied information, is that the circuit layout is mostly responsible for the observed noise.

    Great care is needed when sharing a supply (+5V and GND in this case) between an analog amplifier and a digital circuit that is experiencing fairly high-current (30mA?) transitions. A breadboard will contribute to the noise, as will any wiring that generates excessive digital noise on the amplifier's power supply.
  • Beau SchwabeBeau Schwabe Posts: 6,566
    Try this slight modification to your 5V power supply. Make sure D1,D2, and D3 are all the same and can handle your current requirements. I have used this in Prosthetics, where you have one power supply and you are driving a motor (with load) and trying to keep a micro controller alive and noise free. Also, you probably don't need it for your design, but an inductor say 47uH to 100uH after the supply diodes will further suppress any voltage spikes.

    PWRSUP.JPG
  • Mark_TMark_T Posts: 1,981
    Or just use a second 5V regulator for the analog stuff. That's normal industry practice, separate
    analog and digital supplies and ground planes. Remember audio circuitry can be affected adversely
    by signals at sub-millivolt level, whereas digital decoupling noise and switch-mode converters typically
    produce 100's of mV of noise. 5V regulators cost a few pennies...
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