Here's a neat way to control fan speed.

[Crazy Jayhawk]

Radio shack sells a two-pole 6-position dial switch. In other words, DP6T. I put together a fanbus using these. Mine didn't work when I folded all the wires together to make it fit in a drive bay though. However, I tested the switch beforehand and it functioned exactly as I had hoped, so I know this can work.

I used the 6-wire auxiliary connector from the PSU to get the 3.3V needed for some of these.

H=high, L=low.

H L
12V 0V = 12V
12V 3.3V = 8.7V
12V 5V = 7V
5V 0V = 5V
3.3V 0V = 3.3V
0V 0V = 0V

If your PSU allows it, you can change your fan's voltage from 0 to 12V in roughly 2V increments without having to worry about voltage regulators or heatsinks. Given some time, I can make a wiring schematic for the switch as well.

Let me know if it works for you. :)

[Crazy Jayhawk]

As viewed from the back side of the switch. Turning the dial clockwise increases voltage.

[William]

This is a neat idea on how to increase the voltage of the fan. I like it.

[MadMan007]

Neat idea, though I don't see how it is better than just using Rhoestats. Oh, you could also get a 17V (12V and -5V) setting. Are there any consequences as far as drain off your 5V or 3.3 V rails though? This could affect system stability...

[Crazy Jayhawk]

Originally posted by MadMan007
Neat idea, though I don't see how it is better than just using Rhoestats. Oh, you could also get a 17V (12V and -5V) setting. Are there any consequences as far as drain off your 5V or 3.3 V rails though? This could affect system stability... Not as severe as drawing from the -5 or -12 lines. Those have far lower max. current ratings than either 3.3 or 5.

[FireMogle]

Maybe Im wrong, but couldent you get 17v with 12 & 5 lines a few diodes and the ground? Using the same 3.3 tactic you could also get steps above 12 in 3.3. 15.3, 17, 20.3.

[Crazy Jayhawk]

Originally posted by FireMogle
Maybe Im wrong, but couldent you get 17v with 12 & 5 lines a few diodes and the ground? Using the same 3.3 tactic you could also get steps above 12 in 3.3. 15.3, 17, 20.3. You lost me...

When you use both 12V and 5V on a fan you get 7V since they're working against each other.

I'd need to see a circuit diagram for the idea with diodes and whatnot. :eh?: