Hah. I'm not any kind of engineer. If you feel like it, I'd be appreciative of any evaluation you might have for what I came up with and how I came to rationalize it.

I wanted the thing to be as quiet as possible at all times, and to always minimize the ways in which it can annoy.

Fans, as frequently implemented, are often annoying. They're often noisy all of the time because they lack controls.

Sometimes, they have dynamic controls that suck. Like a Juniper switch that runs the fans at a screaming 100% that you can't have a conversation near during its minutes-long boot process, and then quiets down to only a dull roar (but never any quieter).

Sometimes they suck in other ways: It starts quiet, but then it ramps up in audible quantized steps as cooling demands increase. The very definition of these steps is distracting.

Sometimes, they're just too responsive to be tolerated in the company of humans. The fan speed is always hunting and changing the pitch of the noise it produces, and sometimes this adjustment happens at a discernible and very regular interval that just makes it maddening to be around.

Sometimes, they're arguably even worse than any of that: The fan cycles on and off. It is a jet turbine, or it is silent. There is no in-between.

Sometimes, they're very clever in the worst ways: They ramp up instantly in response to dynamic events, and then slowly wind back down. That's awful in a power amplifier but it happens anyway, wherein: Every loud amplified sound is punctuated by the dying roar of a fan, even when the dynamic event was actually a short-lived nothingburger.

---

Anyway, this one is buttery-smooth. It responds to temperature on a curve. It has no perceptible steps as speeds increase or decrease. It's deliberately lazy and smoothed-out in its response; this amplifier has several pounds of aluminum heatsinks so instant response just isn't ever useful, and it's also least-annoying to deliberately eliminate rapid speed changes altogether.

The fan is a big Nidec screamer that I got from a late-century, grossly-overbuilt Dell Precision desktop. It can reliably spin so slowly that it's essentially silent (as is useful for an engineering workstation like that Dell), and it can also move enough air to fly itself right up and off of the bench.

The controller automatically finds the minimum viable speed for the installed fan, so it avoids being stalled at low duty cycles. In this way, some air is moving regardless of which make/model of 4-wire PC-style PWM fan is used down the road, making potential bush fixes more practical and functional. (It also does stall detection and recalibrates if that's ever necessary for some reason.)

And there's no lookup tables, because lookup tables imply steps and steps are bad. Besides, I'm not trying to save a million nickles on a million units here; shaving pennies isn't part of the program and a single $3 MCU board is cheap for my [qty. 1] application, so that what it gets. By extension, it has way more than enough grunt to get everything done and it just computes it all over and over again.

Like the output %, which gets rejiggered at a rate of 1KHz: I could have probably been happy with 100Hz. Or 10Hz. But the MCU is already chosen and it can do 1KHz just fine, so... that's what it do. It doesn't matter that it is inefficient; efficiency wasn't a goal. :)

And, because it's vibe coded: Of course this big rack-mount power amp from 1986 has a wifi-accessible web interface for its cooling system. It seemed like a pocket computer would be best way to provide a way to twist some of the cooling-related knobs when used in the field, since this is a functional prototype that sometimes gets used in literal fields. (It was dead simple to to get the bot to put that part together. The networking stuff might have been the easiest part.)