SpoolSense - An NFC Smart Cap with display
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Reads your spool's OpenPrintTag (NFC) and displays it on an e-ink display. Based on Prusa's telescopic spool holder.
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Model information
- Source
- Printables
- Category
- Prusa Parts & Upgrades
- License
- Creative Commons — Attribution — Noncommercial — Share Alike
Check the filament left on a Prusament spool on the spool holder before starting a long print.
SpoolSense replaces the cap on Prusa's injection-moulded spool holder for the XL and CORE One+. An NFC reader inside the cap reads the OpenPrintTag label on Prusament spools, and the display shows the material, brand, color and remaining weight. E-ink holds its image without power, so the reading stays visible while the electronics sleep.
The mounting ring is copied from Prusa's original cap model. The cap fits the spool holder exactly like the stock one and twists off by hand for spool changes.
Operation
The NFC reader sits on the back plate, a few millimeters from the tag on the spool flange.
On wake, the ESP32 reads the tag and calculates the remaining weight as net weight minus consumed weight.
It then refreshes the display and goes back to deep sleep with the reader powered off but display still on.
The cap reads the tag but never writes to it. The consumed weight comes from PrusaSlicer or the PRUSA app. The display shows the age of each reading for that reason.
Parts to buy
Budget roughly $55 for the electronics and screws.
Part | Qty | Approx. price |
M5Stack NFC Universal Unit (ST25R3916) | 1 | $20 |
Waveshare 1.54" e-Paper Module V2, 200 x 200 | 1 | $18 |
Seeed Studio XIAO ESP32C3 (required: built-in LiPo charger) | 1 | $5.50 |
Adafruit MiniBoost 5V (TPS61023, #4654) | 1 | $4 |
3.7 V LiPo, 1000 mAh, approx. 41 x 32 x 7 mm, JST PH2.0 | 1 | $7.50 |
#4 x 5/8" rounded-head thread-forming screws for plastic | 4 | |
M2 x 4 pan-head screws | 5 | |
M2 x 4 countersunk screws | 3 | |
Hook-up wire, solder and double-sided foam tape |
Do not substitute a PN532 or RC522 reader. OpenPrintTag uses ISO 15693 (NFC-V), which neither supports.
Printing
Doesn't require supports, just print them flat.
File | Orientation | Print time |
adapter.stl | Flat face down, ring up | A few minutes |
rev2_body.stl | Back face down, open side up | About 2 h |
rev2_lid.stl | Front face down | About 30 min |
Use PETG or ASA, not PLA. Slice at 0.2 mm with 3 walls/perimeters and 20% infill.
Print adapter first and confirm the fit on the spool holder before printing the body and lid.
Assembly
Place the adapter against the back of the body and fasten it from the inside with the three M2 countersunk screws with heads flush with the floor.
Remove the display's four brass standoffs and desolder the white cable connector on its back. Solder wires directly to the pads instead.
Wire the electronics following the wiring.pdf guide. Connect the LiPo to the XIAO's B+ and B- pads. Power the MiniBoost from the battery and feed its 5 V output to the NFC reader, with D6 as the enable. Connect the reader over I2C on D4 and D5, and the display over SPI on D0, D1, D2, D7, D8 and D10. Test the full circuit on the bench before installation.
Seat the NFC reader in the centre of the floor, between the four corner stops.
Screw the MiniBoost onto its raised pad beside the reader with one M2 pan-head screw.
Stick a strip of foam tape on top of the reader and press the battery onto it, between the stops.
Set the XIAO on the two support fins above the battery, with the USB-C port in the wall slot.
Screw the display onto the four corner posts, screen up, with four M2 pan-head screws through its corner holes.
Fit the lid, whose rib holds the XIAO in place, and secure it with the four #4 screws.
Upload the firmware over USB-C, slide the cap onto the spoolholder and load a spool.
Charge the battery through the same USB-C port.