Given that it is for a sub, the water shouldn't slosh around all that much.  Why
not use a float?  It is probably a little larger than you want, and perhaps
you'd rather have a non-mechanical sensor, but for ease of assembly and reading
and simple float setup with a pot or rotary encoder can't be beat.

When you do go to another expiremental method, it would be benificial to have
the float working as well so you can compare the readings and improve your
design, before getting rid of the float.

-Adam

Andy Shaw wrote:
>
> Hi Folks,
> I'm trying to put together some sort of sensor to measure the amount of
> water in a model sub ballast tank. The requirements are:
> 1. Must be small (not a lot of space).
> 2. Easy to seal against water.
> 3. Continuous range from say 1 cm to say 30 cm deep, with 1mm accuracy.
> 4. Possibly best not to use anything that depends upon pressure (since this
> may vary depending upon sub depth).
> 5. Easy to hook up to a PIC (either digital or analogue OK  - I have both).
> 6. Cheap!
> Not asking much!
>
> I seem to remember seeing a rain gauge project that used two (insulated)
> wires separated by a fixed gap as part pf some sort of oscillator. But guess
> what I've lost the mag. Anyone got the details of know if this would work
> for me?
>
> Thanks
>
> Andy
>
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http://www.piclist.com hint: The PICList is archived three different
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