Bin project

How to weigh wastes

I'm searching for a very cheap system to measure bin's weight.
Weight sensor cost three dollars while a potentiometer thirty cents. so, I'd like to try to make a mechanic system with springs, rack and gear as a weight sensor.

Weigh system

A vertical translation on springs due to wastes weight can be transformed to rotation with involute rack and gear and turn a potentiometer wich resistance changes. By reading analogic voltage, I can measure weight.
I draw mechanic system on Freecad using FcGear addon.
Springs, coming from promotional pen, are 5mm diameter and 32mm length. There length can be reduced to 12mm.

Weigh system Freecad file