Hi!
I'm noob at eletronics, but I want to build/buy a device with frequency/voltage converter, to grab impulses from a proper fan wire, and send it as a constant voltage to simple voltmeter like this, but with lower scale:



I need to get preview of 3x120mm fans I've mounted recently. Their wires are to short, so they are plugged into random connectors all over motherboard, at max speed, it's noisy. I already ordered a cheap device to control their rpm by one potentiometer

Here's another exemple:


I would be grateful for any help.
Cheers!

http://en.wikipedia.org/wiki/Computer_fan_control

http://lifehacker.com/5866009/control-your-computers-fan-speeds-for-better-performance-when-you-need-it-silence-when-you-dont