ASP - Just another spool holder
But -this spool holder is special !
It has an load cell implemented
The theory :
Load cell - an electronic device for measuring the weight of something. In this case the filament spool. You can calculate the leftover length of the filament if you know the weight and the specific density of the material.
The weight is proportional to the resistance of the load cell, its also proportional to the voltage, finally you got an value for calculation the leftover length of the filament on the spool. Of course we measure the spool and the printed parts too, but we can substitute it, because they are well known.
You can buy cheap load cells with A/D converters from eBay.
I recommend an load cell with max. 3kg for 1kg spools and a cell with max 5kg for the big 3kg spools. I bought an 2kg cell, its just at the end of the max. range !
OK, there is an display missing. I have some OLEDs in spare which I bought for some months.
The “rest” is an Atmega with some BASCOM coding