I wanted a filament spool holder that would indicate the weight of filament remaining on the spool. So I have designed and built one. I use an Ender 3 and prefer the filament to be positioned at the side of the printer instead of on the spool holder on the top.
I made the holder section first to make sure the filament rolled off smoothly. This section can be used on it's own, without the scales, if you don't fancy any of the electronics malarky.
Included in the documents section is a wiring diagram and a list of parts. The website links supplied are the ones that I used (in the UK) and should at least give you an idea of the parts used.
The base of the scales is available in two versions. One has a large hole (16.5mm) for the on/off switch that I used and the other has a small hole so that the hole can be drilled to the required size. On the base of the unit I fixed some silicone pads to ensure the scales do not move during use.