The weigh station on a workbench: a black enclosure with a 3.5-inch display and a round grey platform with an orange centering cone

The 3D-printing lab at Seattle Makers goes through a lot of filament, and it is hard to tell how much of any of it is left. This scale fixes that.

How it works

Set a spool on the scale and it tells you what the spool is and how much filament is on it, and it updates the shop inventory with the new weight.

Every spool carries a small NFC sticker in the OpenPrintTag format, the open standard Prusa created for identifying filament.

Place a spool on the platform and the station:

  1. reads the tag: brand, material, colour and print temperatures;
  2. weighs the spool and subtracts the empty spool’s weight;
  3. records what’s left, both in its own inventory and back onto the tag, so a Prusa printer reading the same tag sees the same number.

Onboarding new inventory

A brand-new sticker is applied to the spool, and staff then fill in what the spool is on the station’s management web page, by scanning the barcode on the box if there is one, or by searching a filament catalogue. Spools that arrive with a vendor’s tag already on them are picked up as they are.

The station's screen: Seattle Makers, Place spool to begin, the web app address and a QR code

Everything lives on the scale

There is no server and no cloud account. The station keeps its own records and serves a web app over the lab’s WiFi; the QR code on the screen opens it. From there anyone can see:

  • Inventory: every spool, what it is and how much is left;
  • Reorder: what’s running low against the lab’s list of filaments to keep in stock;
  • Usage: grams (and dollars) used per month per material, which tells the lab what members actually print with;

and staff can restock, run a shelf audit, back up and restore, and calibrate the scale.

Inside

A SparkFun ESP32-S3 board, a PN5180 NFC reader, a load cell with a NAU7802 amplifier, and a 3.5-inch display, in a 3D-printed enclosure. The firmware is C++ on PlatformIO and FreeRTOS. Everything needed to build one is open source: the enclosure models, wiring, bill of materials and firmware.