Hej Roman Black. Tack f=F6r ditt meddelande 18:36 2002-08-31 enligt nedan:
>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?=20

I=B4m thinking about that :)

Also, using hearable frequency also make it serve as audible function=
 indicator :)

>Ping it at it's
>(dry) resonant frequency and use the PIC ADC to
>examine the ringing.

Or count cycles in a short defined time.

> 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

Yes, but i think it will be damped too quickly, both by water taking away=
 power, and by the silica gel (or whatever) sealing.

Some standard piezos have a third terminal that is used to drive itself a=
 drive transistor at exact self resonanze.  I thinkt that will give a more=
 clear response.  Just turn the power on for a short time, wait until decent=
 amplitude, then count cycles during a few ms, and shut down to rest a=
 while.

I just have not seen a small standard piezo with that third terminal, but i=
 think it is easy to etch or mechanically carve out a third terminal on a=
 small piezo.

Thank you all for your input.
-Even more ideas are welcome :)

/Morgan

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