[adamrmcd]

I am absolutely loving the author's explanation on WHY each component was selected, placed, and caveats.

The interactive schematics and gerbers are subtle but very effective.

Overall a very clear design and tone I really need to follow for my own PCB projects.

[theacodes]

Author here, thank you for the kind words! My goal is always to write the thing I would've wanted to have when I started out.

[scottwick]

Fantastic write up - thank you! I also love hearing about why each part was chosen. As an electronics hobbyist I often mimic portions of others' designs but I'm not always entirely sure why a certain part was chosen among the various options.

Do you prototype all this on a breadboard before making the PCB and picking specific parts? I'd be curious to hear more about your process. I feel like I always need to test everything I build on a breadboard first since I inevitably miss some small detail if I go straight to schematic + PCB design.

[theacodes]

Great question! It really depends. If I'm working with a part I haven't ever worked with before, I'll often make a minimal breakout board that I can talk to with a devboard like an Arduino or Feather.

If I'm pretty familiar with everything, I generally dive into a rough PCB layout and debug from there. If I absolutely can't get anything to work, I'll go back to the drawing board and possibly do some little breakouts, for example: https://twitter.com/theavalkyrie/status/1457845661370568709

Edit: for this specific project I did make breakouts for testing the MOSFETs and solenoid drivers. I'm glad I did, since I was able to try out a couple of different options for each: https://twitter.com/theavalkyrie/status/1550878465876004865

[jakewins]

Second the poster above, really enjoyed the reasoning around how and why you picked parts and the intent of various circuits..

Do you have any books you recommend on electronics? I feel I understand the basics, like what various components do in isolation, but would love to level up and understand circuit design like how you are approaching it here

[theacodes]

I'll echo sibling's comment about just doing it. Theory only takes you so far, it's important to actually build and experiment, even if it's just in a simulator.

I can recommend Practical Electronics for Inventors as a solid base of projects to experiment with and learn from. If you want to learn how to improve circuits and optimize for specific behaviors, there is a wealth of information in manufacturer application notes. A lot of the protection circuitry used in my article follows advice found in application notes.

[caraffle]

IMO the best way is to just pick a project and work on it. Using application notes and datasheets lets you piece together circuits, and you pick up design patterns along the way.

[shadowpho]

Beautiful write up! I love seeing those flyback diodes and ESD, many DIY and even products avoid them and product suffers.

One thing I wanted to add - I recommend placing a large-ish cap (22u) when using ferrite bead\inductor, as you can get ringing/oscillation otherwise.

[philsnow]

Usually when I read through a build-out description like this, the author writes it for an audience that has a lot more background knowledge than I do. This article, on the other hand, was lucid and the explication helped me follow along.

I got to the part about 3.3V being derived from 5V and thought to myself "why not get it from 24V?" and then just a tiny bit later, there's the bit about USB and how Starfish can just take 5V from the USB host, and it clicked.

I also learned about Sparkfun's QWIIC connector in the aside about the chosen i2c bus switch having two "extra" channels. Love it, thanks for the article, Thea.

[theacodes]

Thank you for the kind words! I'm glad it was useful.

> why not get it from 24V?

There are DC-DC converters in that same family that can do 4.75~36V -> 3.3V, but since I needed the 5V anyway for the LEDs and I/Os, tossing an inexpensive and small LDO for 5V -> 3.3V is an easy call.

[a9h74j]

FWIW, when I was thinking more about text-based literate circuit design, one of the advantages I thought of was to leave ample place to comment upon selection rationale for (and subsequent experience with) particular components.