>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).

So you want to try a wet resistance type of sensor with unknown (changing)
water of unknown temperature and make it accurate to 0.3% ? I hope that
your analog design and electrochemistry knowledge is in the range
between excellent and amazing, because you will need it.

Most subs do not stay on even keel most of the time so you actually need
two sensors and average the read heights. Given the size it sounds more
like a 1/2 caliber torpedo than a model sub ;-)

Now, a pair of capsulated potentiometers or torsion transducers and a pair
of small floats will probably get you near there (if 2% is near enough).
You can easily average the two readings in analog mode before converting
to digital. Don't forget to account for when the fish is standing on end
;-). And do not rely on gravity to keep the floats on the surface of the
liquid, use springs.

good luck,

Peter

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