Genome wrote:

> Maybe you can use 1 LM35 temp sensor then tie a heating coil around it
> and cover it with maybe some epoxy. Measure the initial temperature of
> the water.. then heat the lm35 through the coil a few degrees above the
> initial reading and then wait for the time it took for the LM35 to cool
> back.. the time elapsed would be a good indication of flow speed
> change.. you just have to calibrate it with some empirical
> measurement... this way its cheap though maybe not be too accurate..

Something like this can work, but you'll have a real hard time to measure
the cooling time. It's an inverse exp function, and it slowly smoothes down
to 0. It's not easy to measure the exact point in time when it goes below a
certain threshold. The error (in time) can easily become bigger than
desired. 

Gerhard

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist