“The internet isn’t exactly short of fan speed controller projects – nor am I. I’ve probably got about four or five variants of these I’ve built over the years. Recently I’ve taken the time to round up the “best of” these into a single open-source friendly AVR based project. Historically it was based on PIC microcontrollers, using various expensive proprietary compilers – the main reason I’ve not released it to-date.
The initial reason I embarked on this is because back 10 or so years ago when I first built one, PC motherboards lacked intelligent fan speed control, and if they did have it, it was limited to the point of being practically useless. The situation is a lot better these days, but the level of control sometimes desired isn’t a given. I still have quite a few of these in use for non PC scenarios, for example, inside networking equipment with excessively noisy overkill cooling arrangements.”