The Revel comes with a built in 25 gallon fresh water tank. WB provides a system to monitor the level from OnePlace. This design only uses 3 sensors glued to the tank wall to decide what level you're at. It's very vague and inaccurate. I wanted a more accurate solution. So I started looking.
My selection criteria included, easy install, not too expensive, no permanent modifications and reasonable accuracy. Turns out this was kinda a high bar.
I looked into the marketplace (internet) and found two possibilities. One, from Garnet (https://www.garnetinstruments.com/holding-tanks/), uses a better sensor technology and is good to a 0.25" of tank level. HOWEVER, you need to use their display unit and it's only available in a few configurations - none of which I wanted. It was also a bit expensive. The other, from Topargee (https://www.topargee.com.au/), is based not on tank level, but water used. It's a flow meter you need to place in the cold line. This design had few problems, you need enough line before and after the meter to create a non-turbulent flow - which forces issues around where to mount it. It also needs to be told when you fill and if you fill less than all the way - I don' t think you can figure out where empty is. There's also a plethora of float/sensor solutions, which I think are clumsy and you typically have to modify or have access to the top of the tank.
I decided to build my own. We're on a well and I have to monitor my system. I've used hydrostatic pressure sensors for years to monitor my well and holding tank levels. They're reliable, and accurate. However, they usually are expensive.
Well it turns out China makes a lot of cheap stuff and I found this sensor for < $40. (https://www.amazon.com/gp/product/B09B399GZQ). I chose the 0-2M version, but might have been OK with the 0-1M unit. This is a 4-20mA type sensor with 24v excitation requirement. I figured I would make a simple Arduino based controller if I used a 12 to 24v buck converter and a FET to turn it on and off.
A friend suggested I look into the ESP32's and I found one variant with OLED already mounted (https://www.amazon.com/dp/B07DKD79Y9) for <$20. So with the major components chosen I whipped up a little board and sent it out to OSHPark for fab.
When the board came back from fab - I populated it and tasted it out. Seems to work. (As per my usual I screwed up some components so had to do a bit of "retrofitting").
The hydrostatic sensor has a "nose cone" that protects the diaphragm. It screws on and I was able to remove it and made a pipe adaptor.
I also modified my van plumbing so that there would be a "T" basically at the drain line (lowest point). I added a ball valve after the "T" so I could fool around with my project. For the electrical side, I added a couple of pigtails to patch into the power for the water pump. So, after plumbing it in and wiring it up. I filled the tank and took an A/D reading at full.
Then emptied the water tank, one gallon at a time - till empty - taking a reading at each point. Lo and behold the resultant graph came out looking pretty good to me. I was happy to see the sensor seemed to give pretty linear and equally spaced data, implying (at least to me) that the sensor was sensitive enough for this application. If I did it again, I would probably get the 0-1M sensor.
In the simplest case, this would be a straight line. However, the shape of the tank affects the amount of water at a given depth. So this curve is specific to my tank in the Revel. The bottom portion of the tank is much smaller in cross section (as it goes over the rear of the wheel well, this makes the slope shallower in the above graph. Using Excel to curve fit the two regions yields a couple of equations
Now that I've got it installed (albeit with kinda temporary masking tape wire management), I need to take it out on the road. Hoping to do that soon so I can test it. I'll use to convert counts to gallons! If this is accurate to +/- 0.5 gal I'd be happy, but I think it might be closer to +/- 0.1 gal. I also don't know if I'll have to have a calibration for elevation. If so, it would be pretty easy (I think) to correct by adding another pressure sensor to determine atmospheric pressure.
If it works, I'll probably mount the display right in grill vent below the Nautilus in water proof manner.