Nikodem Bartnik, apparently unsatisfied with the normal sized dot matrix printers available, decided to design and make his own 3D-printed version, capable of producing prints that are 55cm wide, and theoretically infinite in length. The device works by pulling a roll of paper under its x-axis gantry which holds a pen, along with a tiny servo motor that it uses to lower the writing instrument and stamp dots in just the right place.
The setup is controlled via an Arduino Uno board, and a processing sketch running on a computer is used to read the image to be printed and send it to the control hardware. In a first for Bartnik, he got the control PCB professionally fabricated for this build, allowing for cleaner results that he could have gotten by doing it himself.
Mechanically, in order to make it as simple as possible, while still functioning correctly, quite a bit of time was spent designing it in Autodesk Fusion 360. One of the more clever aspects of the design is that the parts under the gantry snap in place like puzzle pieces, and he even printed the rollers with flex filament to obtain a better grip on the paper.
Be sure to check out the printer in action in the video below; the results are quite pleasing!