Mechanical Keyboard Receives Rotary Dial Upgrade

Many of us love vintage technology, but it can be difficult for us to find a place for it in our lives. Retro computers struggle to run modern software and they can’t even connect to the internet if you go back more than a couple of decades. Old stereo equipment doesn’t play today’s streaming music without the addition of an external media box. And landline phones are almost obsolete among today’s cellular smartphones. But Squidgeefish found a use for an old rotary phone dial as a replacement for a keyboard’s numeric keypad.

Squidgeefish completed this project for a coworker who inherited a vintage rotary phone from his grandparents. The coworker enjoys retro aesthetics, but couldn’t find a use for the landline phone. Squidgeefish came to his rescue with this project. Starting with a cheap mechanical keyboard, Squidgeefish replaced the 10-key numeric keypad with the old phone’s rotary dial. By dialing a specific number, the user can enter that digit as if they were pressing the corresponding numeric key. To avoid cheating, Squidgeefish also put a big dummy key cap across the top row of numeric keys so that users have to use the rotary dial.

The rotary dial works in a manner very similar to my own volume control project. As the dial spins back from the selected number, a switch momentarily makes contact as it passes each digit. By counting the switch pulses, one can find the dialed number. It isn’t clear what microcontroller or development board Squidgeefish used (they refer to it by the proprietary eponym “Arduino”), but it seems to be capable of acting as a USB HID — just like a regular keyboard. By plugging both it and the mechanical keyboard’s USB cable into a USB hub, the computer will accept alphanumeric input from both. Of course, the rotary dial is only sending numeric digits.

The rest of Squidgeefish’s work went into packaging. Because the original 10-key portion of the keyboard was unused, they were able to cut a hole in that portion of the PCB for the rotary dial to fit into. A 3D-printed cover for that area tidies up the case and a 3D-printed key cap covers the standard numeric keys. Squidgeefish designed those 3D-printed parts in OpenSCAD, which is code-based parametric CAD software popular with programmers.

Squidgeefish reports that the rotary keyboard received quite a lot of attention in the coworker’s office. Reactions ranged from pleasant surprise to sheer disgust.