Sensor used is a VL53L0X which can be bought from AdaFruit or AliExpress for a few dollars. It uses a laser to measure distance to the surface in mm. Mine has a 'lens' to make it waterproof, hopefully. The disadvantage of this lens is that it is less accurate and needs an offset. This project has been tested on my boat but is not doing as expected because there is some kind of reflection that causes the gauge to never go below 40%. So I will look for another kind of sensor; pressure probably.
