In essence, it’s like connecting a small capacitor in parallel to a large one. The small tube is one wire, the atmospheric pressure serves as the “ground” in the electrical case. As the small cap drains, it is continually replenished by the large one. Or, the capacitance is the sum of both capacitors.

Seriously, though, agree about putting the inlet below the water line (most pets hate surprises!) and switching to at least a solid-state sensor, if not a mechanical control/ballcock. Maybe if you’re going to have it be microcontroller-based anyway, you could set up an automated nightly “flush” system, and have a computer-controlled outlet valve that runs to a drain somewhere? Open the drain, wait a few minutes, close it, run the water till it fills, open the drain, wait, close it, and refill. Guaranteed fresh water daily. Shouldn’t even be hard/expensive to add the extra kit, though I guess people have a spare fresh-water hookup in more places than they have a spare sewage/drain line.

Just one thought… pets eat poop and drink urine… do we really need to change their water?
;-)

Add a UV light to kill bacteria…tada, safe

the automated empty/fill pump is a good idea.

use a tube to fill the tub from the bottom, rather than pouring it in from the top, possibly with a diffuser over the end of the tube, to minimize the sound and motion that might scare a cat away

If you do that, restrict the flow to something extremely low, to further reduce the disturbance in the water. your cat likely will not be drinking large amounts of water quickly, so you don’t need a huge inrush of water to fill it back up.

That should sufficiently reduce the cat scaring qualities of the thing.

As far as all the other stuff about making it double-redundant etc, that seems like overkill. Just use a Normally closed valve and a robust sensor and i think you’d be fine, though you may want to put this in a place where overflow will cause the least amount of damage, just in case.

-Taylor

the real problem lies in the fact that when your animal drinks, the bacteria from their mouth is left in the water. if you keep adding water and never replace it, the bacteria stays and grows. take a few minutes and leave fresh water for your animal!

my cat would just sit on it

but a microcontroller timers and capacitance sensors are probably safer.

First, there should be two tanks of water, at the same level, connected with a tube. This will allow you to fill the secondary one while keeping it a few feet away, and protected in a box to prevent the float being displaced or the animal being frightened. A small second float switch set a bit higher could easily cut off the flow if the first ended up stuck open.

Second, another tube off the drinking bowl should go to pump (a fish tank pump would work) also stored in the hidden box. Periodically (once per day?) the pump should engage (a cheap timer switch would do) for long enough to empty the contents of the drinking bowl — changing the water.