🖨️ Raspberry Pi Label Server (Zebra GK420d)

This project turns a Raspberry Pi (2 Zero W) into a fully automated print server for shipping labels. It monitors a network folder that runs on the pi itself, automatically detects common German shipping carriers (DHL, Hermes, etc.) by filename, crops the PDFs to the correct size, and prints them on the Zebra GK420d (you can change it to any pritner you want).

Quick Start

1. Open the Network Folder:

   • Windows: \\<IP-OF-YOUR-PI>\LabelPrinter
   • Mac: smb://<IP-OF-YOUR-PI>/LabelPrinter

2. Drop a PDF:

   • Copy your label PDF into the input folder.

3. Magic:

   • The original file is immediately backed up to the original folder.
   • The PDF is analyzed and cropped/rotated based on the filename.
   • The printer outputs the label (4x6 inch).
   • The processed file is moved to the processed folder.

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Folder Structure

The Samba share LabelPrinter contains three subfolders:

Folder	Description
input	Drop files here. The watchdog monitors this folder for new PDFs.
processed	Contains the cropped/final PDFs after successful printing.
original	Contains the unmodified A4 originals as a backup.

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Automated Logic (Modes)

The script checks the filename to determine how to process the label:

Type / Keyword	Action	Details
DHL "DHL-Paketmarke"	Crop	Removes typical A4 margins, keeps only the label area.
Hermes "Hermes", "Paketschein_"	Crop + Rotate	Cuts off the bottom half of the A4 page and rotates the label by 90° so it fits the 4x6 portrait format.
Return Label "Rücksende-Etikett"	Crop	Fallback for older Hermes return labels (bottom crop).
Stamp "Briefmarken"	Crop + Scale	Isolates the stamp (e.g., Internetmarke) and scales it up.
Amazon / Other	Direct Copy	No modification, printed via fit-to-page.

Note: All print jobs are sent to CUPS with the -o fit-to-page option to ensure they fill the 4x6 inch label.

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Technical Setup & Maintenance

Paths on the Pi

• Python Script: /home/admin/print_watchdog.py
• Label Directory: /home/admin/labels/
• System Service: /etc/systemd/system/labelprinter.service

Important Commands (SSH)

Check Status (Is the service running?):

sudo systemctl status labelprinter.service

Restart Service (After code changes):

sudo systemctl restart labelprinter.service

View Logs (Debugging):

# Live logs (Exit with CTRL+C)
journalctl -u labelprinter.service -f

Edit Script:

nano /home/admin/print_watchdog.py

Installation / Disaster Recovery

If you need to set up the system from scratch: Install Dependencies:

sudo apt install cups python3-pip
pip install watchdog pypdf --break-system-packages

Configure CUPS:

• Web Interface: https://:631
• Driver: Zebra ZPL Label Printer
• Name: Zebra_GK420d
• Media Size: 4x6 inch (or 100x150mm)

Configure Samba:

• Config file: /etc/samba/smb.conf
• Create share [LabelPrinter] pointing to /home/admin/labels (guest ok = yes).

Setup Service:

• Create /etc/systemd/system/labelprinter.service.
• Enable it: sudo systemctl enable labelprinter.service.