[Cialug] OT: Defunct CPU Fans ?

[Morris Dovey]

Matthew Nuzum wrote:
|| On Dec 26, 2007 10:16 AM, Morris Dovey <mrdovey at iedu.com> wrote:
||
||| Anyone have any non-working CPU fans? I'm trying to build an
||| airflow sensor and think one of these tiny fans (with magnets
||| removed) might work for an anemometer...
|||
||
|| Would you mind sharing the theory of operation on this?

I plan to place the fan in the airflow I want to monitor (convective
exhaust from a passive air-heating solar panel) and sense the fan's
RPMs. I'm hoping to develop a flow velocity from fan RPM, but for
immediate purposes (comparing the behavior of different absorber/heat
exchanger designs) just having the RPM will be sufficient. At this
stage I'm still not sure whether I'll be able to develop an accurate
flow velocity with the fan.

At the moment, I'm planning to attach a small lightweight notched disk
to the center rotating hub, and use an opto-isolator to sense the
notch and drive a 32-bit counter. The count will be the number of
rotations since the count was last read, since the counter
automatically resets each time it's read.

The counter will be a DS2423 from Dallas Semiconductor, and will be
daisy-chained in a 1-wire net. There's a bit more info on what I'm up
to at

   http://www.iedu.com/DeSoto/Projects/Monitor/

and you can see a typical panel installation at

  http://www.iedu.com/DeSoto/SC_Madison/

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto