For those collecting and refreshing the Tandy/Radio Shack business computers from the 1980s, many face the immediate problem that these old keyboards no longer work. The main problem stems from the foam that causes the keys to return to their up position after a press, has degraded into more dust than foam.  There are kits and methods of restoring these keyboards, but it's messy, time consuming, and fiddly.

So, why not use a modern USB keyboard?  Several years ago John Elliott IV and I put together such an adapter that used a Raspberry Pi Zero/W and a custom carrier board plus some Adafruit breakouts to do this.  At that time the least expensive way to do a host USB adapter was the Pi Zero. It booted into a read only Linux version we put together and works very well.

But, users didn't like the 30 seconds it took to boot and I kept an eye out for an inexpensive USB host adapter that might be made with a microcontroller.  What I found was the Adafruit RP2040 Feather with USB Host. Jeff Epler used a couple of RP2040 boards to build a CP/M microcomputer--one board did the CP/M and the other was the keyboard coprocessor.  This was pretty exciting and with the MIT license it looked easy to adapt into a version 2 of the keyboard adapter.

https://www.hackster.io/news/jeff-epler-turns-two-adafruit-feather-rp2040-boards-into-a-fully-functional-cp-m-microcomputer-ee2a95b123dc

https://blog.adafruit.com/2023/06/14/new-guide-rp2040-runcpm-emulator-with-usb-keyboard-hdmi-screen-cpm-retrocomputing/

The short version of the story is that I added modifications to Jeff's code to emulate a Tandy Radio Shack keyboard for the Model II/16/12/16B/6000 line of computers.  With the exception of the base Model II and base Model 12, all came equipped to run XENIX, a UNIX derivative multi-user system operating on these dual processor, Z80/68000 systems. I designed up a carrier board, a 3D printed box, and instructions.

I'm a seat of the pants programmer and I'm sure that there are better ways to make these mods to Jeff's code...  But it does work very well. Check out https://www.tandy-emeritus.org for more information.