Thank you for pitching in on this, cth515. It does make sense that decoupling the “noise making device” (the microcontroller) better would help cure the noise…although I’m pretty sure that I tired this with the noisy unit that i had and it didn’t help…but i was using a lower capacitance (around 220nf) so it makes sense that a much higher capacitance would make more of a difference. The board version shouldn’t make a difference of how well this works. The ground planes and power distribution path are very similar on both board versions. The ground planes are separated (digital and analog), but there are other ways for current to get through.
I’m really glad that you found a solution that works for you! Good work!
Mike353…yes, please go ahead and try this. The cap you linked to is much too large of a capacitance…use one of these:
https://www.taydaelectronics.com/capacitors/electrolytic-capacitors/nichicon-1uf-50v-105c-radial-electrolytic-capacitor-5-11mm.html
https://www.mouser.com/ProductDetail/KEMET/ESL105M100AC3AA?qs=HXFqYaX1Q2x0RWu%2FYCFzZA%3D%3D
https://www.digikey.com/product-detail/en/rubycon/50YXJ1M5X11/1189-1421-ND/3134377
Ideally you want a cap with a relatively low ESR (equivalent series resistance) which gives the noise a low impedance path to ground, but i’m not sure how practically important that is in this application.
Here is a page with a graphic of the Atmega328p IC’s pinout:
http://www.learningaboutelectronics.com/Articles/Atmega328-pinout.php
You can see that pin 1 is near the divot on top of the chip. Pin 1 is also closest to the dot on the IC (although it’s not shown in the graphic). Pin 1 also has a square solder pad, where as the rest of the pins on the IC have round pads. From pin 1 count the pins down to 7 and 8. Please note the graphic is a picture of the IC from the TOP, but you will be soldering the cap to the BOTTOM of the IC, on the solder side of the board. So keep that in mind when finding pins 7 and 8 on the bottom of the board.
Once you think you’ve found pins 7 and 8, test them to make sure you are correct. Pin 7 should be connected to the other 5v pins around the board and on the voltage regulator. Pin 8 should be connected to ground.
Remember electrolytic caps are polarized so the positive lead (the long lead) should be soldered to pin 7 (aka 5v) and the short lead (the negative pin, with the white stripe on the body) should be soldered to pin 8 (ground).
Cut the leads short and lay the body of the cap down on the solder side of the board so the leads are touching pins 7 and 8…then solder the cap leads to the IC’s solder pads. You may want to hold the body of the cap to the board with some hot glue or something to keep it from rattling around so the solder joints don’t eventually break.
Please let us know how this works for you.
Good luck!
-Brach