I recently had a computer cd-rom failure and rather than throwing it out, I decided to use its case for a custom fan controller. The fan controller consists of two components, a 10k potentiometer and a NPN transistor. I used a C1984 in place of the npn transistor because I already had it, but any npn should work. The voltmeter and temperature display just need to be connected and mounted in the cd-rom. Both the 4 digit voltmeter and temperature display came from suntekstore.com for under $8 free shipping and I already had everything else. I decided to use jst power connectors for the fans because I already had a bunch of them.
Step 1: The Layout and Build
I took out all the internals of the cd-rom drive and used a dremel to cut the openings on the face for the voltmeter and temperature display. I used hot glue to hold them in place, and used more hot glue to hold the jst connectors in place at the back. next I drilled a hole at the front for the potentiometer and mounted it, then used an existing hole to mount the transistor with heatsink to the case using a screw. I taped down some the wires to prevent any strain on them. The layout diagram shows how I connected everything. With the components I used the voltage going to fans can be varied between 7.5-11.5 Volts. I am currently using 4 120mm fans and the transistor warms up but does not get hot, again this will vary based on which npn transistor you decide to use.