This is an Arduino powered scale which holds your 3D filament and calculates approximately how much filament you have remaining on your spool in meters. It's fairly accurate (+/- 1 meters when whole spool is on the scale & +/- 5 meters when the printer is pulling on the filament) Closer to the end of the spool, it will get much less accurate as the pull force of the extruder and the spring force of the tighter coiled filament becomes greater than the weight of the spool itself. You should use my remixed spool holder with this scale as it fits perfectly in the tray or you can modify the design to fit one of your own. It can be found here: http://www.thingiverse.com/thing:804325

Use instructions:
When the scale is booting up, make sure not to have the spool sitting on top. You'll first be asked if you're using 3mm filament, if you are, press and hold the "Tare" button for yes.

In the configuration section, you can change the average weight for each diameter filament that you use as well as the average spool weight of your favorite filament for more accuracy.

What you'll need to build it:

• 5 KG Load Cell (http://amzn.to/1GDuutM)
• HX711 Weighing Sensor AD Module Dual-Channel 24-bit A/D conversion Shielding (http://amzn.to/1JGV7V0)
• Arduino Uno (http://amzn.to/1FDVNYJ)
• 20 x 4 LCD screen (http://amzn.to/1DQi4OA)
• Male to Female Jumper wire (http://amzn.to/1JGVy1w)
• Assorted 3m and 4m bolts

The code for the scale can be found at github (including the required library): https://github.com/smokinpuppy/SpoolScale
Library: https://github.com/bogde/HX711

Please read the readme file for instructions on how to calibrate the scale correctly.

Wiring: (Ar = Arduino, Hx = Hx711, Kn = Knob, Bu = Button, and Sc = Scale Bar)
Hx711:
VCC -> 5v (Ar)
SCK -> A3 (Ar)
DT -> A2 (Ar)
GND -> GND (Ar)
E+ -> RED WIRE (Sc)
E- -> BLACK WIRE (Sc)
A- -> WHITE WIRE (Sc)
A+ -> GREEN WIRE (Sc)

LCD J204A:
VSS+RW -> GND (Ar)
VDD -> 5v (Ar)
V0 -> SIN (Kn)
RS -> D12 (Ar)
E -> D11 (Ar)
D4 -> D5 (Ar)
D5 -> D4 (Ar)
D6 -> D3 (Ar)
D7 -> D2 (Ar)
A -> D9 (Ar)
K + (Button + Knob) -> GND (Ar)

Button:
VCC -> 5v (Ar)
SIN -> D7 (Ar)
GND -> GND (Ar)

Knob:
VCC -> 5v (Ar)
SIN -> LCD(V0)
GND -> GND (Ar)