I guess the tl;dr of the article can be summed up as "better not". If all you need is to supply power, than a regular two-pole connector with a fixed voltage will save a ton of work and probably end up more reliable.
No, it's "5V is easy. Anything above that is not."
For obvious reasons. Almost everything can tolerate 5V. Very few things can tolerate 9V and above.
Consequently, you need a complicated dance in order to ensure that everybody agrees before jamming 9V, 15V or 20V down the pipe. That dance has enough complexity that effectively everybody uses a full-blown Cortex M0 with a couple of purpose built analog blocks to carry it out.
For higher voltages, use a barrel plug. There's a de-facto standard of 12V and 20V there, with the latter using a slightly larger plug. As they're used widely in laptops, parts are readily available.
> For higher voltages, use a barrel plug. There's a de-facto standard of 12V and 20V there, with the latter using a slightly larger plug. As they're used widely in laptops, parts are readily available.
If you look at Digikey AC-DC power supplies, you can find about 12K that end in a barrel jack.
Of those 12K, only 6 are not a 2.5mmx5.5mm, 2.1mmx5.5mm or smaller barrel jack. And Digikey seems to not even stock the mating jack for those 6 power supplies.
There is also absolutely no standardization of what voltage level corresponds to which jack. I have about a half-dozen dead Beaglebone Black's over the years because I had two different power supplies on my lab bench for testing and the plugs were "juuuuust" close enough (2.5mm and 2.1mm are compatible enough to let you short things out even if you can't completely seat them) to let me put 12V or higher onto a 5V-only jack.
I use a $2 PD trigger module on basically everything.
The only time I use 2.1mm is when I'm going to daisy chain or do something besides point to point, when I'm doing solar, or when I'm using the connector for something other than power(A voltage divider can protect your input from accidental power connection, so it's one of my favorite simple connectors).
I think they're pretty much all unbranded and look similar, but now there are some with through hole outputs instead of pads to solder wire. If I didn't already have a stash I would probably get those and some right angle male headers.
Just watch out, 12v isn't a thing anymore in the new specs and might not work, best to build around 5v, 9v, 15v, or 20v.
Although usually if I just need 5v, I'm building around a D1 Mini ESP32 module that already has 5v built in.
I saw one in a YouTube build video that allows you to select output voltage / what it will negotiate using a pushbutton, the selection is indicated by the color of an LED (and hopefully persisted when powered down).
Edit: the one chx linked to above is precisely of this kind
I use it when it's 12V, it's probably most popular barrel plug voltage and also used in a lot of audio devices (aside from guitar pedals which have 9V with reversed voltage... fuck that)
-9v is semi-tolerable for legacy reasons, what's really bad is center-positive 5v on what looks like a 1.3mm or so plug, as found in a cheap wireless DMX system. Still beats wired DMX though.
