wondering if this could be modded for a car fuel tank. & possibly on a small boat fuel tank.
This could be done fairly easily, and there are plenty of articles on the internet on how to make a capacitive probe.
This system is designed to read two tanks, so you could eliminate the multiplexer and a lot of the code.
However, there are a few traps to avoid.
Capacitive fuel probes are sensitive to the dielectric value of the fuel being measured.
Large aircraft have a small reference probe always covered by the fuel in order to read the dielectric value and calculate the quantity accurately.
I did not need to worry about this as the specification for avgas is tightly controlled, and this light aircraft operates in a limited temperature range.
The main problem would be with automotive gasoline which varies significantly with various percentages of ethanol added, and a reference probe would probably be needed if reasonable accuracy is required.
Adding a fuel flow sensor to this one would be sweet and opens up some interesting management and reporting possibilities.
That should be easy to do; just some maths to calculate and display the rate of change of the quantity.
I did not need to do this as it was already included on another instrument.
Where can I find the datasheets of your sensor?
It came as part of a Kit from Vision Microsystems Inc, There are other manufacturers serving this market. The probe is fairly simple; just a metal tube with a metal rod on nylon standoffs inside it , combined with an oscillator whos frequency depends on capacitance.
Here are links for the code, circuit and flowcharts.