Well its installed! Yup finally got off my rear and put the thing in the camper.
Had everything all soldered up and ready to go sitting on my desk here waiting for the last thing. The last thing was to figure out where to get power from. I figured there is a really nice switched 12V power right there: The tank heater pads. We never go camping when its cold enough to use them anyway so they are never turned on and when they are they are thermostatically controlled (checked based on the part # on them). Even if the tank heater is on my little Arduino isn't going to draw enough on top of that to make a difference (50ma @ 5V). So now the monitor can be on or off at the flick of a switch.
Took some time to mount it in the back of the bay where the sewer drain is. I figure that bay is pretty dry:
(I'm using really short screws to hold it to the back wall and there is a good 1" or more gap between the back of the screw and anything else back there.)
That is the "sensor": two pieces of copper tape close to each other. The circuit measures the capacitance between the two (which changes with the fullness of the tank).
For now protecting the sensor with some black duct tape. For a more permanent solution I may spray some Flex Seal over it.
There is the circuit ready to be mounted to the wall. (If you'll note behind it is a 9V regulator: Input 12V output 9V. This is because the Arduino circuit I'm using doesn't have the heat sink capacity to drop 12V -> 5V so I put an intermediate regulator in to do 3V+ of the drop.) Yeah I used wire nuts to hold the wires together--what you don't see here is all the electrical tape I covered them with when I was cleaning up the install.
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