I have wired up an ESP8266 wifi uC to a MAX7219 7-segment driver. The setup works well, except that the circuit seems susceptible to external noise. The main issue I have noticed is that activating a light fixture on the same circuit will mess with the device (the display gets scrambled, or even goes blank).

The circuit is currently setup on a bread board with wires everywhere, as shown in photos below. So I thought the issue was just that all these loose wires were acting as antennas (and maybe that is the answer). But the problem seems much reduced if I plug my device into another outlet ("B" on my sketch), which makes me think it is actually a power supply spike and that my circuit is not adequately filtered.

I am powering the whole thing off an old ATX power supply, which I thought would be pretty resilient to mains noise.

I have 10uF and 0.1uF capacitors on the circuit, as recommended on the Arduino site. I think I have the caps fairly close to the leads, especially for the MAX7219. I have tried several combinations of capacitors, but the behaviour seems to be the same.

I am just wondering if I am on the right track with power line issues? Or if I am wasting my time and this circuit will never work properly until I get rid of the "antenna" wires and use a proper circuit board?



full size


  • \$\begingroup\$ Before you transfer the circuit to PCB, you can try a few things. Try to gather the GND connections close to each other - like on a single short line on your breadboard, if you can - and then connect them to the ground of your power supply with a short wire. Check out "common impedance noise" for a clearer explanation :) \$\endgroup\$
    – C K
    Feb 8, 2017 at 5:37
  • \$\begingroup\$ The ceramic 0.1uF bypass capacitor is not effective at that location 50mm from the IC, because it is still too far from the IC; those long wires (and the solderless breadboard itself) add unwanted inductance to the supply and ground return. Put the 0.1uF directly across pins 4 to 19, directly over the IC. Although this does make it a little less convenient to swap out the IC, removing the extra wire length as much as possible, helps the bypass capacitor actually do its job. See also: electronics.stackexchange.com/a/247670/35022 \$\endgroup\$
    – MarkU
    Feb 8, 2017 at 6:07


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