Posted by: gdunlap Jul 10 2006, 02:37 PM

I wanted to describe here how I wired my Cooler Master blue LED base fan to indicate drive activity.

Pin 39 of the 40-pin IDE cable gets pulled low whenever there's activity so what can be done is to connect that to the negative side of an LED. The other side of the LED can be connected to +12v or +5v through a current-limiting resistor (without the resistor the LED will quickly burn out!) If you're using the +5v line to power the LED then a 100 ohm resistor will probably work well.

With an LED fan the resistor is already built in, so all I needed to do was disconnect the LEDs' negative wire inside the fan and bring it out to be connected somehow to IDE line 39. Originally I had simply soldered it to the cathode (negative) side of the activity LED on the mainboard, but I later decided that was too inconvenient and dangerous so I changed it to the IDE-DVD adapter attached to my internal superdrive instead.

Although it was unnecessary, I decided to provide 5v power as well for possible future use. The LED wire from the fan ends in a PC-case-style LED connector (with just the cathode wire though) salvaged from a PC case; to mate with that I cannibalized a 3-pin fan connector and pulled out two pins. I soldered a wire from the remaining center pin to IDE pin 39 on the back of the DVD adapter, pushed one leg of a 100ohm resistor (trimmed for length) though an adjacent hole in the former fan connector, and soldered a wire from the other leg of the resistor to the +5V pin on the DVD adapters power connector.

Even though I don't currently need power from that connector, I can always plug in a regular LED there if I ever need to.

The base of the Cube now glows blue with disk activity :)

Attached are some pictures:

Here's the fan:


Here's the adapter:


And here's the adapter on the drive (with my home-made mounting bracket)