2017-06-25, 10:33 PM
Interesting project. I just finished a simple three-level indicator for my water tank. It is simply a plastic rod with a ground terminal on the bottom, then three more contacts wrapped around the rod to indicate low, medium and high level in the tank. I use an arduino to show four lights, the bottom indicating no contact and critically low (flashing), and three more LEDs to indicate the level. I've seen commercial versions of this sort of thing available that use a probe with 2 to 5 rods of varying lengths that go down into the tank. I might have done it that way if I had been able to find some non-corrosive rods, but the plastic rods with bare copper wire wrapped at intervals seems to work fine. I installed it a few days ago and it works great. I guess at some point I could use firmata (and MQTT?) to bring that data into Openplotter. That sounds like what you are thinking about.
When I was researching the project, I came across a commercial product for RV water and waste water tanks that used capacitance between two parallel strips of adhesive aluminum foil attached to the outside of plastic or fiberglass tanks, which sounds like something similar to what you are doing. Rather than using several patches, it used two strips, and (I think) measured the change in capacitance as the liquid level changed. I suppose if I had seen that prior to starting on my project, I might have tried that, but I don't need to know water levels down to a percentage!, I only need to know when I need to start looking for a water fill station!
As for generating Signal K names, have a look at the Signal K generator. I think you'll find keys there for what you need.
When I was researching the project, I came across a commercial product for RV water and waste water tanks that used capacitance between two parallel strips of adhesive aluminum foil attached to the outside of plastic or fiberglass tanks, which sounds like something similar to what you are doing. Rather than using several patches, it used two strips, and (I think) measured the change in capacitance as the liquid level changed. I suppose if I had seen that prior to starting on my project, I might have tried that, but I don't need to know water levels down to a percentage!, I only need to know when I need to start looking for a water fill station!
As for generating Signal K names, have a look at the Signal K generator. I think you'll find keys there for what you need.