Padoca: hotkey keyboard

Online meetings became widespread during the 2020 COVID pandemic. Call etiquette mandates that you keep your microphone muted while not talking, as almost everyone knows. This mute-unmute dynamic inspired me to search for a more comfortable solution that didn’t involve pressing multiple keys on the keyboard or reaching for the mouse every time. Luckily I stumbled upon this Instructable by FabroLabs Technologies . I decided to give it a try and build a hotkey keyboard from scratch: the casing, circuit, firmware, and keycaps.

Although I have some previous experience with modeling and sculpting in Blender 3d, I am not acquainted with CAD software. Because of this limitation, I decided to start by designing the casing, and after experimenting with FreeCAD, Fusion 360, and OpenSCAD, I decided to stick with the latter. In OpenSCAD’s workflow, you don’t interactively model a 3D mesh. Instead, you write scripts that describe 3D objects, ending with a parametric description of the mesh that can be easily adjusted.

Screenshot of OpenSCAD with the keyboard design
Designing the keyboard using OpenSCAD

After I developed the casing, I iterated by printing the parts that would later fit a component to check for any sizing mistakes. The following pictures show some of those tests.

A hand holding a piece of the case with an LCD attached
Not the best first layer but useful to check measurements

Assembling the circuit was pretty straightforward. I used an Arduino Pro Micro, a KY-040 rotary encoder, a 1602 LCD, Gateron blue switches, 1N4148 small-signal diodes, and some current limiting resistors. I assembled the switches in a matrix with the diodes used to prevent ghosting as described in this post .

The opened case with the wiring of components
The wiring of the switch matrix

During the final assembly, I found the spaces between switches to be small for conventional keycaps. Since I was using rsheldiii’s excellent KeyV2 lib for generating them, I only had to reduce the width to 14mm. This is the printed knob from Thingiverse and the final product looks like this.

Final assembled hotkey keyboard with the LCD display on
Close-up of the LCD with the text [00] Debug
It is possible to switch between different profiles

If you want to build your own hotkey keyboard, I’ve open-sourced all the resources needed in this repository .