PC fan question

[clone]

OKAY.. so i have a question about PC fans... when you take them out of ur computer, they have 3 wires.  usually red black and yellow.

what is the 3rd wire for?? is it a temperature indicator? or a fan speed monitor?? what can i use this third wire to do??

thnx, dave

[HDL_CinC_Dragon]

the yellow wire is for fan speed monitoring

[clone]

excellent.. so what kind of signal does it send out.. does it send out a certain voltage or resistance that would indicate the speed?? how would i hook it up to an arduino board to detect fan speed?

[HDL_CinC_Dragon]

not really sure TBH... Im going to assume it would be a digital signal which the PC counts the on and offs per second... ive never hooked up an O-Scope to it to be sure.

try googling it

[Razor Concepts]

It's some kind of frequency counter output. Look here
http://en.wikipedia.org/wiki/Computer_fan

[Admin]

As with all electronics hacking, if you don't know what signal it gives out, hook it up to a multimeter

[frodo]

i am not very good with multimeters and have googled which didn't return much (nothing), so how do you test which signal something sends with a multimeter?

[Admin]

i am not very good with multimeters and have googled which didn't return much (nothing), so how do you test which signal something sends with a multimeter?

You definitely need a multimeter to make robots!

Put the black wire on ground, and the red wire on the wire you want to test. Then set the multimeter to the test you want. Use google to learn more about how to use a multimeter

[fuzzyt]

This might help explain things.

http://www.comairrotron.com/fan_monitoring.shtml