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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