[MisterTea]

You're over thinking it. If the application is very simple and needs to do one thing, an analog system works fine. Once you start needing sequencing, multiple adjustments, and maybe a little smarts then a CPU can get involved.

I worked at a shop that had an old closed loop water-air chiller for a laser. The water temperature controller was a small PCB with an op-amp chip with some passives and the temperature was set by a potentiometer. That thing ran fine until the compressor died and it sent to scrap.

[dv_dt]

My analog fan control comment was a bit tongue-in-cheek, but turning a knob on a potentiometer to adjust fan speed has some personal appeal - no digging around for a sw utility, no poking interfaces to see if the motherboard mfr bios exposed the control, of if it exposed it but doesn't actually hook the right plug, no adjusting to see if the right temp input is reading correctly. Fewer layers of things to go wrong can be so nice.