This is a spool holder that I made a few years ago that uses a 5kg Load Cell Weight Sensor.  The electronics and the programming will need to be figured out, u-tube is your friend with the research. I went through a few variations and ended up using a ESP32  to read the load cell, control lighting and monitor the temperature inside my enclosure that I built.

Surprisingly, this is very accurate and could determine within a few grams of filament left on a spool. 

 I mounted the base to the floor of my enclosure, but I am including the step file for anyone who wants to redesign their own base. The base also has 2 M5 nuts that will need to be embedded inside of it. The nuts are used to secure the load cell (side with wires) to the base using M5 x 35 screws.

The spool holder is then fastened to the opposite side of the load cell with 2 M4 x 40 screws

Load cell link

NAU7802 24-Bit ADC I used this instead of the HX711's that came with the load cells

Bearings These are for the rollers, which I seem to have deleted, but can easily be re-created

OLED's to display the data on. That's a whole other project.

I will update as needed