bambuddy/spoolbuddy

SpoolBuddy Hardware Setup

PN5180 NFC Reader (SPI)

Wiring

PN5180 Pin	Raspberry Pi Pin	GPIO	Wire Color
3V3	Pin 1	—	Red
5V	Pin 2	—	Red
GND	Pin 20	—	Black
SCK	Pin 23	GPIO11	Yellow
MISO	Pin 21	GPIO9	Blue
MOSI	Pin 19	GPIO10	Green
NSS (CS)	Pin 16	GPIO23	Orange
BUSY	Pin 22	GPIO25	White
RST	Pin 18	GPIO24	Brown

Power: The PN5180 board has two power pins. 3V3 powers the IC itself, 5V powers the antenna booster and extends read range. Both should be connected. Do NOT connect 5V to the 3V3 pin — it will destroy the reader.

NSS: We use GPIO23 for manual chip-select instead of the default SPI CE0 (GPIO8) because the kernel SPI driver's automatic CS timing does not meet the PN5180's requirements (5µs setup, 100µs hold). Manual CS via GPIO23 with spidev.no_cs = True resolves this.

Setup Steps

1. Enable SPI and I2C

After a fresh Raspberry Pi OS install, SPI and I2C are disabled by default.

sudo raspi-config
# Navigate to: Interface Options -> SPI -> Enable
# Navigate to: Interface Options -> I2C -> Enable
sudo reboot

Verify after reboot:

ls /dev/spidev0.*
# Should show: /dev/spidev0.0  /dev/spidev0.1

ls /dev/i2c-*
# Should include: /dev/i2c-1

2. Configure /boot/firmware/config.txt

Add the following lines under the [all] section:

# SpoolBuddy: I2C bus 0 for NAU7802 scale (GPIO0/GPIO1)
dtparam=i2c_vc=on

# SpoolBuddy: Disable SPI auto CS (manual CS on GPIO23 for PN5180)
dtoverlay=spi0-0cs

• i2c_vc=on enables I2C bus 0 (GPIO0/GPIO1). The default i2c_arm only enables bus 1 (GPIO2/GPIO3). The NAU7802 is wired to bus 0.
• spi0-0cs disables the kernel SPI driver's automatic chip-select. We use manual CS on GPIO23 because the driver's CS timing doesn't meet the PN5180's requirements.

Then reboot:

sudo reboot

Verify after reboot:

ls /dev/i2c-0
# Should exist

sudo i2cdetect -y 0
# Should show 0x2A (NAU7802)

3. Install system packages

sudo apt install python3-spidev python3-libgpiod gpiod libgpiod3 i2c-tools

• python3-spidev / libgpiod3 — system libraries for SPI and GPIO access
• gpiod — command-line GPIO tools (useful for debugging)
• i2c-tools — I2C diagnostic tools (i2cdetect, i2cget, etc.)

4. Install Python dependencies (in venv)

pip install spidev gpiod smbus2

• spidev — Python SPI bindings (PN5180 NFC reader)
• gpiod — Python GPIO bindings via libgpiod (works on both RPi 4 and RPi 5)
• smbus2 — Python I2C bindings (NAU7802 scale)

5. Solder all connections

Wago connectors or breadboard jumpers are unreliable for SPI — the PN5180 is very sensitive to signal integrity issues (loose connections cause RF field flickering, phantom errors, and intermittent communication failures). Solder all wires directly for reliable operation.

6. Verify hardware communication

Run the diagnostic script to confirm the PN5180 is responding:

sudo python3 spoolbuddy/pn5180_diag.py

Expected output includes product version (e.g. v4.0), firmware version, register dump, and "Diagnostics complete" at the end.

7. Test tag reading

sudo python3 spoolbuddy/read_tag.py

Place a tag on the reader. Supported tag types:

Tag Type	SAK	Use Case
MIFARE Classic 1K	0x08	Bambu Lab filament tags
MIFARE Classic 4K	0x18	Bambu Lab filament tags
NTAG (213/215/216)	0x00	SpoolEase / OpenPrintTag

Troubleshooting

Symptom	Cause	Fix
All zeros from SPI reads	SPI not enabled	Run raspi-config and enable SPI, then reboot
GENERAL_ERROR on SEND_DATA	Automatic CS timing too fast	Use manual CS on GPIO23 with spi0-0cs overlay
BUSY timeout	Wiring issue or RST not connected	Check RST and BUSY pin connections
RF field flickering on/off	Loose power wires	Solder all connections
No tag found but tag is present	Wrong protocol or missing setTransceiveMode()	Ensure ISO 14443A config (0x00, 0x80) and setTransceiveMode() before every SEND_DATA
Auth failed for block N	Wrong key derivation	Verify HKDF uses context "RFID-A\0" (7 bytes including null terminator)
EBUSY when requesting GPIO8	Kernel SPI driver owns CE0	Use GPIO23 for NSS instead

Technical Notes

• SPI speed: 500 kHz (higher speeds cause communication errors)
• SPI mode: 0 (CPOL=0, CPHA=0)
• CS timing: 5µs setup after CS LOW, 100µs hold after CS HIGH
• BUSY handshake: wait for BUSY HIGH (processing started) then LOW (done) — waiting only for LOW is incorrect
• setTransceiveMode(): must write 0x03 to SYSTEM_CONFIG bits 0-2 before every SEND_DATA, or the PN5180 buffers data but never transmits on RF
• Bambu tags use MIFARE Classic with per-sector keys derived via HKDF-SHA256 from a master key + tag UID
• NTAG reads require CRC disabled (unlike MIFARE Classic which needs CRC enabled)
• The PN5180 handles Crypto1 encryption/decryption internally via the MFC_AUTHENTICATE (0x0C) host command

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NAU7802 Scale (I2C)

Wiring

NAU7802 Pin	Raspberry Pi Pin	GPIO	Wire Color
VCC	Pin 1	—	Red
SDA	Pin 27	GPIO 0	Yellow
SCL	Pin 28	GPIO 1	White
GND	Pin 30	—	Black

I2C Bus: Uses I2C bus 0 (GPIO0/GPIO1), enabled via dtparam=i2c_vc=on in config.txt. Bus 1 (GPIO2/GPIO3) is the default but those pins are not used here.

Verify

sudo i2cdetect -y 0
# Should show 0x2A

sudo python3 spoolbuddy/scale_diag.py

The diagnostic reads 10 samples at 10 SPS and shows raw ADC values, average, and spread. Typical idle readings are around ~500k with a spread under 20k.