Morgan Olsson wrote:

> I still believe most in acoustic method, where i can demand a large part of the cavity to be filled before detection.  Water is the only matter nearby that is plenty enough to fill it. (within reason)


Ok, maybe the acoustic method can be simplified?
With ultrasonic piezos etc you get ringing after
the initial pulse train is sent. Maybe you only need
one piezo element, and can use something cheap and
common like a commercial buzzer? Ping it at it's
(dry) resonant frequency and use the PIC ADC to
examine the ringing. I'm sure once it has any
significant amount of water on the piezo the
resonance (and ringing) at the test freq will
vary noticeably.
-Roman

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