Troubleshooting¶

Problems the scale cannot work out by itself: network, backend, tags, the Pi.

Check the status bar first

Anything wrong with the hardware, the scale diagnoses itself and says so in plain words. Every message it can show, with cause and fix, is under What the scale is telling you.

Scale¶

Scale shows 0 or doesn't respond

Does the LED on the NAU7802 light up? If not, check power - 5V on Pin 1, GND on Pin 2 of the WT32 I/O connector
Check load cell wiring (E+/E-/A+/A-)
If values are negative, swap A+ and A-
Recalibrate via Settings → Scale → Calibration

Scale shows an absurd number, e.g. -3487423847234 g

That number is not a measurement. When the I²C bus is broken, every register read comes back as all ones, which the firmware reads as "conversion ready" plus a sample of -1. Fix the bus first, the number follows.

Open the serial monitor at 115200 baud and look at the boot line I2C_EXT scan: - it lists every address that answers. Expected: 0x24 PN532, 0x2A NAU7802
Repeated [E][Wire.cpp:499] ... returned Error -1 means "no device acknowledged". That is a wiring fault, not an address conflict: 0x24 and 0x2A cannot collide, and the touch controller sits on a separate bus
Check the solder joints while the plug is seated. A cold joint measures fine on the bench and opens under strain
SDA (Pin 3) and SCL (Pin 4) not swapped, GND (Pin 2) continuous

Weight is still wrong after fixing the wiring

A calibration taken while the bus was broken is stored in the device and survives the repair.

Settings → Scale → Reset calibration, then TARE and calibrate again with a reference weight

Scale weight is inaccurate

Recalibrate with a precise reference weight (~1000 g recommended)
Make sure nothing touches the weighing platform during tare
Avoid vibrations during measurement

Scale reads correctly but Spoolman diff is wrong

Check if the spool weight is set correctly in Spoolman
Update bag weight via Settings → Scale → Bag weight

NFC¶

NFC reader not detected on boot

Does the LED on the PN532 light up? If not, check power - 5V on Pin 1 of the WT32 I/O connector
Check PN532 jumpers - must be set to I²C mode
Verify wiring: SDA → Pin 3, SCL → Pin 4, RST → Pin 7
Do not connect PN532 via NAU7802 STEMMA QT passthrough (only 3.3V)

NFC tag not recognized

Hold the spool steady directly over the NFC window
Try a different NTAG sticker - some cheap stickers have defects
Not sure if your tag is compatible? See the NFC tags

WiFi & Network¶

Device doesn't connect to WiFi

SpoolmanScale supports 2.4 GHz only - 5 GHz networks will not appear
Double-check password (case sensitive)
Move closer to the router during setup

Can't reach Spoolman from SpoolmanScale

Make sure Spoolman is running and reachable from another device on your network
Use the IP address, not a hostname
Check port - default is 7912
Verify both devices are on the same network

Firmware¶

Device doesn't appear in Web Flasher

Use a data-capable USB-C cable (many cables are charge-only)
Try a different USB port or computer
Use Chrome or Edge - Firefox does not support WebSerial

OTA update fails

Check WiFi connection
Try again - the GitHub download can time out on slow connections
Fall back to the Web Flasher or manual file upload if OTA keeps failing

Display shows nothing after flashing

Re-flash via the Web Flasher

SpoolmanScale Pro (Pi)¶

Can't reach spoolmanscale.local

On Windows: install Bonjour Print Services
Use the Pi's IP address directly as an alternative
Check that the Pi is powered and connected to WiFi

Backend doesn't start after reboot

Check systemd service: sudo systemctl status spoolmanscale-backend
Check Docker: docker ps
Check logs: docker logs spoolmanscale-ui

Still stuck?

Join the Discord - the community is happy to help.