Raspberry Pi (single board computer) based Hardware Print Server with REST API to print on ZPL enabled label printers.
- Raspberry Pi 4 Model B 4 GB RAM (Conrad: 2138865)
- Kühllörper Raspberry Pi (Conrad: 2247647)
- Raspberry Pi 4 Enclosure (Conrad: 2140254)
- Raspberry Pi 15W Power Supply EU (Conrad: 2140238 - VQ)
- 16 GB Micro-SD-Card Class10 (Conrad: 1421772 - VQ)
- ZD411d for 5 cm labels (batch label)
- Zebra GK420d or Labelident BP41 for 10 cm labels (shipping labels)
Download Raspberry Pi Imager and download a fresh image of Raspberry Pi OS onto the SD Card. We recommend using Raspberry Pi OS Lite (32-bit). Set the advanced settings like hostname and passwords before flashing the image, so you can reduce configuration efforts. This can be done in Raspberry Pi Imager with the gear symbol, before flashing.
- Username: "nprint"
- Password: "smart4pi"
Connect to the device through SSH (replace with actual IP address). Log in with user "nprint" and password "smart4pi".
ssh nprint@10.1.1.128 $
Update Raspberry Pi OS and all packages with apt-get package manager by running this command:
sudo apt-get update -y && sudo apt-get upgrade -y && sudo apt-get dist-upgrade -y &&
sudo apt-get autoclean -y && sudo apt-get clean -y && sudo apt autoremove -y &&
sudo apt autoremove -y
sudo raspi-config
Go to System Options → Hostname example: nprint-we1.de.newmatik.com
After setting the hostname, reboot once.
sudo apt-get install -y vim git python3-pip
The system uses CUPS as the print server. Install:
sudo apt-get install -y cups cups-client lpr libcups2-dev
CUPS uses the user group “lpadmin” to know who is authorized to administer the printers. After installing CUPS, add our user "nprint" to the user group “lpadmin”:
sudo usermod -a -G lpadmin nprint
Because we want to connect to the admin page through our computer we need to allow the admin page remotely. We will also set that we share our printers in the network. This will require us to restart the CUPS service after the changes have been made to take effect.
sudo cupsctl --remote-admin --share-printers --remote-any
sudo systemctl restart cups
After installing CUPS and adding a user, or set of users, to the user group lpadmin, the rest of the configuration can be done via the CUPS Administration page. You can access this page on the Raspberry Pi by opening a web browser and going to the address: http://10.1.1.128:631/ (replace with actual IP address).
sudo apt-get install -y ufw
# SSH and DNS
sudo ufw allow ssh
sudo ufw allow dns
# Flask Development Port
sudo ufw allow 3000
# CUPS IPP Printer Sharing
sudo ufw allow 631/tcp
sudo ufw allow 5353/udp
# CUPS IPP Printer Sharing
sudo ufw allow 137/udp
sudo ufw allow 139/tcp
sudo ufw allow 445/tcp
# Enable UFW
sudo ufw enable
CUPS can announce its presence on the network via mDNS (multicast DNS) and DNS-SD (DNS Service Discovery) protocol, which is also known as Bonjour. In order to do that, you need to install and run avahi-daemon, which is a service similar to the Apple Bonjour service that allows computers to automatically discover shared devices and services on the local network.
sudo apt install avahi-daemon -y
sudo systemctl start avahi-daemon -y
sudo systemctl enable avahi-daemon -y
sudo ufw allow 5353/udp
Because macOS and most Linux desktop distributions have CUPS installed as the default printing system, once you have enabled printer sharing via Bonjour/IPP on the Ubuntu box, macOS and Linux users in the same network can automatically use the printer. When they click the print option in applications (word processors, email readers, photo editors, and web browsers), the printer will be automatically available. They don’t have to explicitly add the printer.
sudo apt install cups-ipp-utils -y
sudo systemctl restart cups
Connect the printers to your Raspberry Pi via USB connection. In our case we will connect a Zebra ZLP 2824 Plus as a batch label printer and a Zebra GK420d as a box label printer.
Open the CUPS admin page http://10.1.1.128:631/ (replace with actual IP address) and add a new printer. Select the local barcode printer e.g. "Zebra Technologies ZTC TLP 2824 Plus (Zebra Technologies ZTC TLP 2824 Plus)". Set a logical name, description and location.
Name: WE1-Batchlabel Description: WE1 Batch Label Printer (ZLP2824 Plus) Location: WE1 Select Network Print share
In step 5 select the Model (e.g. "Zebra ZPL Label Printer (en)") and press Add Printer.
Under "General" configure the label size. In our case we select "custom" label size with 53x55 mm size with 203 dpi. Web Sensing and "Direct Thermo Transfer Media" as standard settings. Go to "Printer Settings" before saving and adjust darkness to 30 and print mode to "tear off". Set the print rate to the highest print speed.
Now save these defaults and go to the printer page to print a test page.
Name: WE1-Boxlabel Description: WE1 Box Label Printer (GK420d) Location: WE1 Select Network Print share
In step 5 select the Model (e.g. "Zebra ZPL Label Printer (en)") and press Add Printer.
Under "General" configure the label size. In our case we select "custom" label size with 101x152 mm size with 203 dpi. Web Sensing and "Direct Thermo Transfer Media" as standard settings. Go to "Printer Settings" before saving and adjust darkness to 30 and print mode to "tear off". Set the print rate to the highest print speed.
Now save these defaults and go to the printer page to print a test page.
To change the orientation by 180 degrees run the following in the terminal with the correct printer name
lpadmin -p WE1-Batchlabel -o orientation-requested-default=6
For basic concepts of how this REST API is built, check out the following resources:
- https://auth0.com/blog/developing-restful-apis-with-python-and-flask/
- https://flask-restful.readthedocs.io/en/latest/
Clone the project into your home folder. This will create the project folder at "/home/nprint/NPrint":
clone https://github.com/elexess/NPrint.git
cd NPrint
brew install pipenv
Install pipenv requirements through PIP:
pip install pipenv
pipenv --python 3.9.2
Install the PIP requirements (Pipfile) through pipenv:
pipenv install
Copy .env_sample to .env and modify as needed:
cp .env_sample .env
Modify the API-KEY in .env or keep the default API-KEY "g897hdfsgo987oh9gbinuhjvc". Make sure to change the API-KEY on a production system.
We have to edit the $PATH variable to be able to run flask directly.
To do that, create the file with touch ~/.bash_aliases and then echo "export PATH=$PATH:~/.local/bin" >> ~/.bash_aliases. Please exit SSH and reconnect for the new path to take effect.
Make sure to enable the pipenv:
pipenv shell
To start NPrint in developer mode simply run the following in your NPrint folder:
flask run
Check if the flask app is running by opening the URL in your browser:
http://10.1.1.128:3000/api/ping (replace with actual IP)
Open demo.html to test basic functionality, use Postman or the following CURL examples.
Ping:
curl http://localhost:3000/api/ping
Get Printers installed in CUPS:
curl -X POST \
-H "Content-Type: application/json" \
-d '{"api_key": "g897hdfsgo987oh9gbinuhjvc"}' \
http://localhost:3000/api/printers
Update the API-KEY:
curl -X POST \
-H "Content-Type: application/json" \
-d '{"api_key": "OLD API KEY", "new_api_key": "NEW API KEY"}' \
http://localhost:3000/api/update/api_key
For a full list of API Endpoints check nprint.py