Bash Register

An old cash register with a thermal receipt printer.

Sun 25 January 2026

The Bash Register is an old cash register that my friend and I stuck a Raspberry Pi Linux computer into. It's connected to a thermal receipt printer that prints images sent from the member portal Spaceport running at my local makerspace, Protospace.

Protospace members are able to draw images on the portal:

Draw controls include colour, eraser, size, shade, undo history, and reset. The current drawing is stored in local storage so it doesn't get lost if the user accidentally navigates away.

Once a drawing is submitted, its filename is sent to the Raspberry Pi via MQTT. A simple Python script listens for the message and then immediately downloads and prints it.

All drawings are added to a gallery that can be publicly viewed here:

Printing Garbage Bug

While developing the code, I was having an issue where every second print would output several inches of garbage characters instead of the image. After hours of debugging it seemed related to the height of the image being printed. I used git bisect to narrow it down to a commit where the canvas's height was changed.

It turned out to be a bug with the printer that happens when printing images with a height that's a multiple of 96 pixels tall:

https://github.com/python-escpos/python-escpos/issues/367

The fix for this was simply adjusting the aspect ratio of the canvas on the portal.