Project presentation

Features 

         graph TD
     A[fa:fa-computer-classic Host] -->|Serial RS-232 data| B[fa:fa-microchip Libre-Printer interface]
     A --> |Parallel Centronics data| B
     B -->|fa:fa-usb USB| C[fa:fa-laptop RaspberryPi or Computer]
     C --> Raw[fa:fa-file Raw file]
     Raw --> D[fa:fa-file-pdf PDF]
     Raw --> E[fa:fa-align-justify Text]
     Raw --> F[fa:fa-file-image PNG]
     Raw --> H[fa:fa-file-csv CSV]
     Raw --> I[fa:fa-chart-line Charts]
     Raw -->|fa:fa-usb USB| G[fa:fa-print Modern printer]
     Raw -->|fa:fa-network-wired Network| G

Libre-Printer consists of an Arduino interface and a set of programs designed to pretend to be a Centronics parallel or serial printer. The data received is stored and/or redirected to a modern printer connected via USB or the network.

The interface connects via USB to any computer or microcomputer such as a Raspberry Pi (all models, including the Zero models).

The operation can be summarized in 3 key steps:

Capture data from the sending machine;
Rendering the data in plain text, PDF or image format;
Redirection of the stream to a modern printer (e.g. network printer)

Printer types & protocols supported 

The supported interfaces & devices are the following:

Epson printers:
ESC/P - ESC/P2, 9 & 24 pins thanks to Escapy, that reliably and almost exhaustively interprets the command set to produce searchable PDF files.
HP PCL printers:
Any resolution and format (Ex: 150dpi, 300dpi, 600dpi), color or grayscale thanks to the project GhostPCL.
HP-PGL (Pen Plotters), HP-GL/2-Compatible Instruments, Instruments with GPIB/HP-IB interfaces:
HP 7470A plotter, oscilloscopes (Tektronix, HP), spectrum analyzers and signal analyzers. Thanks to the Free and Open Source Software: hp2xx.
PostScript printers:
Conversions are made thanks to Ghostscript, an interpreter for the PostScript® language and PDF files. Ghostscript consists of a PostScript interpreter layer and a graphics library.
Seiko Quartz Watch Tester Printers:
Specifically the Seiko Qt-2100 Timegrapher device. Thanks to our own project: Seiko Converter

Much more will come depending on the community’s participation in terms of funding, developing or sharing raw device output data for retroengineering purposes.

Connectivity 

Connections can be both serial RS-232 and parallel Centronics (DB-25 on one end, 36-pins Centronics on the other).

See the chapter How do I recognise my interface type? for more information.

Project Structure 

Hardware Interface 

Instead of opting for an expensive, low scalability and reverse engineering hindering interface board like the original project, it is cheap chips from the Arduino ecosystem.

Currently (and in a non-limited way) it is an Arduino ProMicro from Sparkfun; copies of which are available on many resale sites.

This chip has enough pins to accommodate a parallel interface without an intermediate component, as well as 2 RS-232 serial interfaces. One of the two serial interfaces is emulated on USB and allows the connection, the exchanges and the update of the Arduino from a simple USB plug (we avoid the proprietary connectors or the limited use of a RaspberryPi HAT).

Softwares 

The core software collecting the data interpreted by the interface can be executed on any machine running GNU/Linux.

Since 2026 we provide a much better and very powerful converter (Escapy) for this job.

The legacy backend of the program converting ESC/P and ESC/P2 data is based on the binary of the RetroPrinter project, which has only been compiled for the ARM platform (i.e. Raspberry Pi). An older version is available on all the platforms.

Why this project?

Why a competing project to RetroPrinter?

Because we can.
In short: This is an opportunity to have a better community project than the proprietary version.

Technical considerations 

The original software is not maintainable (close source), without decent software design and unnecessarily cumbersome.
The ESC/P2 converter of RetroPrinter has a “free version” which besides being lightened of some features (missing international charsets, etc.) is offered to be tested for free by the community and then to bring patches in the paid version of their product…
The “free version” is buggy and sometimes not compilable due to “patches” (obviously applied with little testing).
The documentation of the original programs is overloaded, poorly updated, with redundant/overlapping parameters and sometimes non-functional combinations.
The RetroPrinter interface is limited to a handful of platforms and cannot be a usable product for most people without some investment (let’s not forget that in the last few years the prices of RaspberryPi type boards have skyrocketed!). Making the project compatible with all platforms is both an economical and pragmatic choice for its diffusion
Libre-Printer components are much cheaper/more affordable.
We support serial printers without additional adapters.
Multiple interfaces can be connected on the same computer!
Our code is tested with over 95% coverage.

Ethical considerations 

Our solution is truly free: licensed under the AGPL.

It is common to see programs in C/C++ etc. developed not by expertise or by performance research, but rather by a desire to obfuscate code at “lower cost”. RetroPrinter is no exception to this. Thus, the “community” formed around these projects receives few benefits: slow development of patches, lack of know-how for some tasks, paying products, no right to modify or redistribute the program, etc. This behaviour is toxic because the community can neither audit nor improve the products. The most paradoxical thing is that when the proprietary code leaks (and it always does) it becomes a competitor to the original (Cf. Streisand effect; which is precisely what the authors wanted to avoid in the first place.

Finally, quite frankly, let’s be pragmatic, the technologies of the 80’s don’t need proprietary overpriced, overloaded and flawed stuff of the 2022’s… Let’s spread the word.