To start, an Arduino Uno accepts inputs from a keyboard which handles the incoming serial signals from the keyboard. From there, two Arduino Pro Micros ... source code and schematics are available ...

The four-layer PCB is densely packed on both sides to fit in the Arduino Pro Micro Form factor ... and has released all the source code and schematics on GitHub. The PCB design files will be ...

PD Micro is the first Arduino-compatible board with USB Type-C Power Delivery, which allows your project to make use of voltages from 5-20 V. It’s perfect for projects that would require ...

as described in this SparkFun tutorial (actually for the Arduino Pro Micro). Except, I could not get these to work – the compiler balked at compiling them – and I have no idea what thing I have to add ...