Need help with designing and building a custom fanbus!

[jtobrien]

Okay, I'm getting ready to build a custom fanbus and while I have most all the materials, I don't have the resistors or rheostats.

Anyways here's what I want for the fanbus but don't know how to execute:
A) 7v output in addition to 5v and 12v
B) rheostats that can fine tune a whole range of different fans (I mean like low-power or small fans to high-power 120mm fans)
C) bi-colored (or maybe even tri-colored) LEDs to indicate what voltage (or voltage range) fan connector X is putting out for the rheostats.

I'm assuming I'll need a resistor for (A) but what wattage resistor? I know about the 7v trick with the twelve and five volt lines but wouldn't it be simpler to branch off of the 12v line with a resistor?

And what should the Ohms rating for the rheostats be? Is 50 Ohms good? I want to be able to finely tune the fan speeds as much as possible...

As for the LEDs, how would I get a multi-colored LED to change depending on the output of a rheostat? I know how to do it for an SPDT toggle switch but not a rheo.

Thank you in advance for your help!

 

[Arcygenical]

Try asking in the electronics forum... You'll get a much more intelligent response

Your rheostats will have to be at least 100ohms to get a good range on most fans.

You'll need a few transistors to switch the LED... maybe a voltage comparator of some sort.

Or, for 10% of the price, get a sunbeam rheobus