My wife bought a ceramic fountain. It has a pump that draws water
from the bottom and pumps it to the top, so the birds can bathe in it
and it srips down to the bottom again. Looks neat, works nice, kills
some of the road noise.

The problem is that in So Arizona, the water evaporates so fast, I
can't discipline myself to keep it filled. So... I am gonna design a
slick way to sense when the water level is low so it can kick on a
solenoid and pump some back into it. I don't want to use anything
ugly, or big (like a float valve). I had in mind a  non-contact sensor,
perhaps a capacitor. The whole sensor/solenoid deal could then
be automatic.

What would work reliably? I am leaning toward a probe with two
insulated contacts, that I can make part of a tuned circuit; when
the water is missing between the probes, the frequency is at a
certain range, with the water between the probes, the frequency
is detuned. Another idea was to mount a  tiny magnetic float  in
a plastic tube, and when the  float  is high enough, it triggers a
hall device.

Any other ideas? Lotsa talent here. I have piles of PICs, can always
help control the solenoid that way...

--Bob

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