Why not use and optical arrangement and look for fan blade rotation?
You will need two such source/detector pair separated by slightly more
than one half of the blade width.
Just a thought.
Vetri

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Tal
Sent: Wednesday, January 22, 2003 4:03 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: [EE]: protection circuit for cooling system

Hi 2 All

I need an idea for a friend for his cooling system.
the problem is if the fan is stopped or stuck or have any malfunction,
he
want to cut the power to the system immediately.
now, I though about measuring the fan wind or measure the fan current.
which
method is the best way?
do you have any simple idea or a cheap one?

Thanks

Tal

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