Take a look at Bosch's rain sensor at

http://app3.internetwork-bosch.com/webapp/kea/k/en/start/product.jsp?mfacKey=BE_5_REGENS

and also

http://www.schott.com/magazine/english/info96/si096_12_sensor.html

hope this helps
Francisco


Peter L. Peres wrote:

>On Mon, 4 Nov 2002, Alan B. Pearce wrote:
>
>*>>this would make the Piezo very sensitive to vibration -ergo
>*>>when rain falls on it vibration happens voltage occurs. I
>*>>think I've seen water proof Piezo tweeters somewhere so they
>*>>might work.
>*>
>*>I was not thinking of having it like that, I was figuring on having the
>*>piezo unit driven at low level by being the tuned element in an oscillator,
>*>and a PLL to look for frequency shift, or some form of amplitude detection
>*>to look for amplitude damping. It may be that if the level of oscillation is
>*>controlled at a low enough level, then a drop of rain may be enough to make
>*>the piezo element go low enough in Q, or be damped enough to cause it to
>*>drop out of oscillation.
>
>Spent too much time in aerospace ? ;-) A raindrop falls from at least 500
>meters of height and has a minimum size. I'd use a simple microphone
>attached to a drum-like structure (with saran wrap skin I think). This may
>react to other things besides rain.
>
>I still favor the idea of measuring just soil humidity.
>
>Peter
>
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