A Mini Bluetooth Dot Matrix Printer
This ATmega328P-powered device is like a tiny modern-day telegraph printer.
YouTuber Et Discover built a miniature printer that’s controlled by his phone over Bluetooth. The device uses a pen as the marking device and a micro servo and linkage system to move it back and forth. The small strip of paper is advanced by a 24BYJ-48 stepper motor, along with a ULN2003 driver, allowing for sequential control over pen placement.
What’s interesting from a mechanical standpoint is that the pen doesn’t descend to the paper to make each dot, but instead the rig employs an electromagnet to bounce the paper up to hit the pen. A neodymium magnet is embedded in the small printed platform that rises up to receive a dot, and a boost converter is used to produce 24 volts for actuation.
A custom PCB is used here, and available via the video description. It implements a Microchip ATmega328P microcontroller and an HC-05 module for Bluetooth interface. As noted in the video, this isn’t Et Discover’s project originally, but is a modified version of the "mini telegraph" found here. More specifics on how to build one is available there, but you’ll need to be able to read Russian or wade through Google Translate to comprehend the text.