The best way to do this that I’ve found is to build a scale – the lighter the bin is, the more salt you need. I watch it and put a threshold in there or something for alerts. I’m in the process of doing it myself right now using a set of load cells and wood. Take a look at this article about building a human scale, the load cells can handle 50kg so if you use four of them distributed you’re up to 200kg (440lbs). I figured that was plenty of margin for the salt bin.
Anyway, I constructed the thing and it works perfectly and is very accurate. I put a 10lb free weight on it and a 20lb free weight and calibrated it linearly and then stood on it and it showed what I expected. I don’t have a 3D printer so I tapped one of my friends at work who has one to print some load cell holders. I’m very excited to put it into use.
