The Art of Printing - Getting started with label printing on Seiko SLP720RT

In industrial applications, Peakboard Boxes are often connected to other devices. This is true for large manufacturing machines and conveyor systems, but also for smaller devices like printers. We’ve discussed how to use Peakboard with e-ink displays, but we often still find printed tags, papers, and labels in modern logistics processes. In today’s article, we’ll discuss how to integrate a label printer into Peakboard.

For our example, we’ll use a SLP720RT printer from Seiko. Peakboard is based on Microsoft Windows, so it seems obvious to use a Windows driver to communicate with the printer. But we don’t do this, because of performance reasons. Responsiveness is critical in any human-machine interaction. So, our Peakboard application will instead communicate directly with the printer through a TCP/IP connection. This is by far the fastest way to communicate.

In the modern world of label printing, there are two main protocols that are used. They are ZPL (Zebra Programming Language) and ESC/POS (Epson Standard Code for Point of Sale). For our example, we will use higher-level commands provided by the POS data source extension that encapsulate ESC/POS commands.

The extension

To make things as easy as possible, we’ll use a Peakboard extension called “POS Printer.” For more information about this extension, see the POS Printer GitHub or the POS Printer extension page.

In the data source, we enter the IP address and port on which the printer is listening. Our Seiko printer doesn’t provide any web interface for configuration. So, we check the manual to find the network configuration.

Prepare the Peakboard application

The actual Peakboard application is pretty simple. Besides the data source for the printer connectivity, we also add three combo boxes. These let the user select the product, the size, and the addition (topping) to be printed on the label.

Our example application is for a coffee shop, where an order is taken, and then a label is printed with all the details about the order. The options for the three combo boxes are taken from three variable lists containing the products, sizes, and additions. The actual magic happens behind the button.

Create the script

The printer data source provides a single function, which triggers the printing process. The function receives a string that specifies the label.

ESC/POS is a protocol that is usually defined by literals and HEX commands for the formatting. For more information, see the ESC/POS command reference. To make it easier for Peakboard users, the POS Printer data source offers simpler commands that are translated into ESC/POS. For more information, see the extension commands.

Although it’s possible to mix both the simple commands and ESC/POS commands, we’ll only use the simple commands in our example. We’ll save the ESC/POS commands for a future article. In our example, we use the following command string:

~(CentralAlign)~~(Image:Starpeak_small.png)~
~(Style:DoubleHeight,DoubleWidth)~~(LeftAlign)~Caramel Macchiato

Size: Large
~(Style:Bold)~
Additions: Cream
~(FullCutAfterFeed:2)~

Here’s a breakdown:

1. The first line prints out the coffee shop logo. It’s a simple PNG image (width less than 300 px) that we added to the Peakboad project as local resource. The preceding ~(CentralAlign)~ centers the image.
2. Then, we have three text parts: the product, the size, and the addition.
3. Finally, we end with a command for cutting the paper.

The whole label is created using the POS Printer extension’s high level language. We don’t use any pure ESC/POS.

The code

The following screenshot shows the Building Blocks for sending the command. We use the placeholder replacement block to replace the three literals in our command string with dynamic values from the user input.

For LUA lovers, here’s the equivalent LUA code:

local _ = data.MyPrinter.print(string.gsubph([[~(CentralAlign)~~(Image:Starpeak_small.png)~
~(Style:DoubleHeight,DoubleWidth)~~(LeftAlign)~#[Product]#

Size: #[Size]#
~(Style:Bold)~
Additions: #[Addition]#
~(FullCutAfterFeed:2)~]], 
  { Product = screens['Screen1'].cmbProduct.selectedvalue, 
  Size = screens['Screen1'].cmdSize.selectedvalue, 
  Addition = screens['Screen1'].cmdAddition.selectedvalue })
, nil)

Result

This video shows the final result in action. It’s impressive that the printing starts almost instantly.