After I completed the project, I made a somewhat lighthearted personal vow to try to design a custom PCB next time I fall down the rabbit hole of hardware tinkering. I suspect, these days it is a commodity skills, and curious if you happen to have any suggestions or articles that could serve as a starting point?

PCBs are a dark art, and I focus on lower-speed (below 30 MHz) to try and avoid any issues.

I know that the faster the PCB is, the more issues you get. Above a certain frequency, inductors look like capacitors, capacitors look like inductors, and PCB-traces look like transmission lines with reflections and other such nonsense. Staying at a slower speed helps negate these issues.

Most application notes, be it from STMicro (for STM32) or Microchip, or really any other microcontroller manufacturerer, will have recommended hardware designs + their thought process fully documented.

Start there. Here's Microchip's ATMega328 hardware design notes: https://ww1.microchip.com/downloads/en/Appnotes/AN2519-AVR-M...

STM32F4: https://www.st.com/resource/en/application_note/an4488-getti...

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Study up on the "reference designs". For ATMega328p, that's Arduino Uno. For more recent AVR chips (such as AVR DD), that's "AVR DD Curiosity Nano". (See schematics here: https://www.microchip.com/en-us/development-tool/EV72Y42A)

The sibling comment is too specialized, I feel. It depends on what you want to do. If you just want to connect a few components together, you can learn the required skills in a day, watch some KiCAD videos.

I made a sensor board the other day (I'm just printing the case for it now), and it was very enjoyable, and even came assembled for $1.7 per board:

https://gitlab.com/stavros/sensor-board

Feel free to email me if you have any questions or just want to chat.

Also, I don't think I've ever wanted something in my life more than this badge thing.

> The sibling comment is too specialized, I feel. It depends on what you want to do. If you just want to connect a few components together, you can learn the required skills in a day, watch some KiCAD videos.

That's fair.

Lets put it this way: if your circuit works on a breadboard, you don't need to know anything about PCB design. The PCB will pretty much always be better than the breadboard.

Things get troublesome as you enter mixed-signal (analog + digital), or high-frequency.

Agreed, but you still need to know a ton of things that seem hard when you haven't done them before. Even exporting the Gerbers, or the BOM for assembly, or any of those things seemed too hard to me before I did it for the first time, so I don't want to underestimate people asking "I want to connect a few components into a custom PCB, how do I do it?".