I use airtight cases for 3DJake's 250g filament spools. But the problem is to know how much filament is left there. So created a kinda smart scale, that tells me the amount in percents.

The case is designed to be attached to the top right part of the Prusa i3 printer's frame by using longer M3 bolts and nuts. A load cell is mounted to the case with two about 15mm M5 bolts and the arm is attached to the load cell with two 15mm M4 bolts.

Parts used:

• 5KG Scale Load Cell With HX711AD Adapter
• ATTINY85 Micro Usb Development Board For Arduino
• 128x32 I2C Blue OLED Display
• Optional: 3.7V to 5V Step Up Voltage Booster

Arduino code: Filament spool scale

Video: https://www.youtube.com/watch?v=gOeVbYkTEuo