So, the PWM controller is done, and works great.
It's butt ugly, but it works great.
Here it is, sealed up with some hot glue, just so nothing shifts around and causes a short:
I ordered a 3 pack of extra drive bay covers from corsair so I could chop one up and install switches and the pot with a dial on it to control my fans.
Middle switch: Fans On/Off
Right Switch: Fans Manual control or auto control based on water temp (if middle switch is on)
Dial: Controls fan speed via PWM
Turns out the front panel on Corsairs Obsidian series bay covers is textured sheet metal. It is glued somehow to the plastic part of the bay cover underneath. I pried the metal part off using a contractor knife. The goo from the glue was intense. Took lots of goo-off to clean both sides. Then I carefully drilled/dremeled holes to fit my two switches and my pot dial in the metal front, and went nuts with my dremel on the plastic to make everything fit in the back.
I was going to glue them back together again, but I think the screws that tighten the switches and pot to the panel do the job, so it's not needed.
The hole locations weren't exactly perfect. I measured them precisely, but kept slipping with the damned drill when I went to drill them. Should have used a punch to start the holes, but I couldn't find mine. I don't think I can tell that they are misaligned, but if it winds up bothering me, I have three more spare Corsair drive covers to re-do it on.
I wiped the damned thing down, but it appears to be statically charged, and clings to all the dist from my dremeling. Will have to do a more careful cleaning when I put it all together.
If anyone is curious, this is what the final result looks like once installed in the case. (I really should have wiped down the front better before taking this picture, and maybe I shouldn't have been lazy and used my DSLR instead of my cell phone )
Click for larger:
I'm by no means a seasoned case modder, but I am happy with how it turned out. It's not perfect, but neat enough, and it definitely works as intended.