There are hundreds of keyboard models available for sale these days. There are keyboards with mechanical and dome switches, there are models with and without numpad, there are keyboards with card readers and trackpads. But there are no modern keyboards with a vintage rotary phone dial that serves as a numpad. But apparently it is possible to build one yourself.
The Rotary Keyboard project by Squidgeefish (via MiniMachines.net) is not exactly meant to enable new functionality or increase productivity, but rather than to make an Aprils Fool prank. For the same reason, the keyboard lacks not only its numpad, but also its numeric row as well to make the prank actually work.
Arguably the biggest challenge with attaching a vintage rotary phone dial to a modern device is that it is analog and produces a pulse train instead of a signal. By contrast, modern keyboards are digital, so there is no way to make the dial work without installing any additional parts. So Squidgeefish took a DFRobot Beetle Board based on the ATmega32U4 chip which has 10 digital pins, five analog pins, four pwn pins and can be programmed to read a pulse train with a simple program while still maintaining compatibility with a standard USB interface.
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Physical installation of a rotary dial looks quite challenging too as it entails cutting a printed circuit board without really knowing which traces go where. Yet, after several attempts the modder managed to make things work. To make the keyboard look more or less aesthetic, Squidgeefish had to 3D print some parts, including the dial and the replacement for the numeric row which just had to go to make the dial worthy.
The end result looks strange, but it works: the dial can be used to input numbers and symbols. It has nothing to do with steampunk keyboards with typewriter-style keys, but this was not the point of the project anyway.
The whole cost of the project was probably lower than $30, but it certainly took a bunch of time to assemble it and make it work.