Anyone have a recommendation for something that can take 2 USB in and be the USB device to 2 separate up stream systems? I’d like to build something can pass through a keyboard and mouse to 2 systems but also embed some hot key actions and the like so it always works regardless if my preferred OS install is configured and booted.
The Teensy is very popular for acting as either USB host or peripheral and there's lots of projects to draw ideas and code from. The latest one only has 2 physical USB ports, so you would have to use a hub for your use case. I don't think you'll find a microcontroller with 4 physical ports anyway.
You want 2 or more off CH9350 - HID mouse/keyboard to serial adapters - they are designed for exactly your application. Wire back-to-back and piggyback an ESP of your choice on the serial ports to eavesdrop/intercept/augment. Available from Ali.
