Two makers, Þórarinn and Arni, built a serial bridge that turns a laptop keyboard into a USB HID input device for any headless machine. No spare keyboard needed. No cluttered desk. Just two RP2040 boards and a serial cable.
The architecture is deliberately minimal: the K in KVM, nothing else. The laptop runs a serial terminal in transmit-only mode. One RP2040 handles USB-to-serial on the laptop side. The second RP2040 converts that serial stream into USB HID keyboard events on the target machine, a Raspberry Pi or anything else expecting a standard USB keyboard. Keystrokes travel down the wire and appear local. Code is published and available. Anyone with two RP2040 boards can replicate this today.
The full write-up is worth reading for the implementation details, specifically how the HID descriptor is constructed on the receiving RP2040 and how the serial framing handles timing. This is a tool that belongs in every hardware lab. Once initial setup is done, SSH takes over and the bridge is retired until the next headless bring-up.
[READ ORIGINAL →]