OpenSpool: Build an NFC Filament Reader for Your 3D Printer

Oct 11, 2026 · 6 min read

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Assembled OpenSpool Mini kit with Wemos D1 Mini S3, PN532 reader, and WS2812B LED mounted on the custom PCB

What You Will Build and Why It Is Useful

OpenSpool turns a Wemos D1 Mini S3 and a PN532 NFC module into a filament-aware reader that sits beside your 3D printer. You stick NTAG 215 or 216 NFC stickers on every spool, write the filament metadata (type, color, brand, min/max temperature) to each tag once, then tap a spool against the reader whenever you load it. The ESP32 reads the tag and pushes the settings to your Bambu printer over MQTT — no manual menu navigation required.

The project targets Bambu printers first (X1C, A1, P1 series), with OctoPrint support in progress and Klipper/Moonraker, Prusa Connect, and Spoolman planned. Schematics are published under an open license and the firmware runs on ESPHome, so the whole stack is inspectable and hackable.

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What You Need

Hardware — with custom PCB (recommended)

Hardware — without custom PCB

Replace the MOSFET and resistors with a 3.3 V–5 V logic level converter and a mini breadboard. All other parts remain the same.

Software

• Chrome or Edge browser (for web-based flashing at openspool.io)
• OR: macOS/Linux with esphome installed via Homebrew and make
• A Bambu printer with its IP address, serial number, and LAN Access Code to hand
• For X1C running firmware 1.08.05.00 or newer: LAN Mode and Developer Mode must be enabled in the printer settings

Typical use cases

How It Works

Each NFC sticker holds a single NDEF record with Content-Type: application/json. The payload is a small JSON object:

{
  "protocol": "openspool",
  "version": "1.0",
  "type": "PLA",
  "color_hex": "FFAABB",
  "brand": "Generic",
  "min_temp": "220",
  "max_temp": "240"
}

When a tagged spool is tapped against the PN532, the ESP32 reads this record and publishes the filament data to the Bambu printer's MQTT broker on port 8883 (MQTTS). The printer then applies the settings as if you had selected the filament through its own interface.

The WS2812B LED gives visual feedback: breathing blue means the device is broadcasting its own access point waiting for Wi-Fi credentials; solid white means it is connected to your network and ready to scan tags.

The PN532 communicates with the Wemos D1 Mini over SPI. On the custom PCB, a BSS138 MOSFET and two 10 kΩ resistors handle the 3.3 V–5 V level shift. On a breadboard build, a discrete logic level converter takes that role.

Assembly

With the custom PCB

1. Solder two 10 kΩ 1206 SMD resistors and one BSS138 MOSFET onto the PCB.
2. Solder four sets of 8 straight headers into the two pairs of columns on the top of the PCB.
3. Solder one set of 8 right-angle headers into the row of vias just below the OpenSpool logo on the back of the PCB.
4. Solder three right-angle headers in the top-left corner of the PCB.
5. Solder eight right-angle headers onto the top side of the PN532.
6. Solder three straight headers onto the LED — on the side with the Din pin.
7. Place the Wemos D1 onto the headers and solder it in. USB-C port faces the bottom of the PCB.
8. Flip the toggle switches on the PN532 to SPI mode.
9. Use jumper wires to connect the PN532 and the LED to their respective header rows.

Without the custom PCB

Follow the wiring diagram in the repository (images/OpenSpoolMiniWiringDiagram.png), using the logic level converter on the mini breadboard in place of the MOSFET and resistors.

NFC scanning tips

• Small red PN532: tags read best near the corners of the antenna.
• Larger blue PN532: tags read best at the center of the antenna.
• Counterfeit PN532 modules are common and often unreliable — buy from a reputable source.

Flash the Firmware

Option 1 — browser (easiest)

Open openspool.io in Chrome or Edge and follow the web-based programming tool. No local toolchain needed.

Option 2 — command line (macOS/Linux)

Install ESPHome and clone the repository:

brew install esphome
git clone https://github.com/spuder/OpenSpool
cd OpenSpool/firmware

Put the Wemos D1 Mini into flash mode: hold the D0 button, press Reset, then release D0. A new USB serial device will appear.

ls /dev/cu*

Flash for the S3:

USB_ADDRESS=/dev/cu.usbmodemXXXXX make lolin_s3_mini

Or for the S2:

USB_ADDRESS=/dev/cu.usbmodemXXXXX make lolin_s2_mini

First-time Wi-Fi setup

After flashing, the ESP32 broadcasts a Wi-Fi network called OpenSpool. Connect to it, open a browser to 192.168.4.1, enter your home Wi-Fi credentials, and reboot. The device will then appear on your network as openspool-xxxxxx.local.

Printer configuration

Navigate to the web interface and enter your printer's IP address, serial number, and LAN Access Code. Reboot the ESP32. A checkmark next to MQTT in the web interface confirms a successful connection. Factory reset is available by holding the D0 button for 10 seconds.

Extending OpenSpool and Known Limitations

Ideas to extend it

• Print the OpenSpool Mini enclosure from MakerWorld and mount the reader on your printer frame for a clean permanent installation.
• Write NFC tags for every spool in your collection using any NFC-capable Android phone or the openspool.io tag writer — the tag format is plain JSON, so any NFC writing app that supports NDEF text records works.
• Monitor raw MQTT traffic with the MQTTX client to debug printer communication or build your own integrations on top of the same broker.
• Contribute a pull request for OctoPrint, Klipper/Moonraker, or Prusa Connect integration — all are listed as planned and the project is actively accepting contributions.

Current limitations

• Bambu is the only fully supported printer integration; OctoPrint, Klipper, and Prusa Connect support is in progress or planned.
• Bambu X1C on firmware 1.08.05.00 or newer requires LAN Mode and Developer Mode to be enabled.
• Bambu A1 and P1 printers allow a maximum of four simultaneous MQTT connections; exceeding this causes clients to disconnect.
• The OpenSpool protocol requires NTAG 215 or 216 tags (>500 bytes). Bambu's own MiFare Classic 1K tags can be read (in progress) but not yet written.
• The Wemos D1 Mini S2 has less RAM than the S3 and may disconnect from the printer occasionally under load.

Facts in this article come from the project's public README and GitHub metadata at the time of writing. Images belong to their respective owners and link back to the original source.