any USB keyboard and mouse to PS/2 adapter?

[ebastler]

Most older USB keyboards, and some current models, can „speak” PS/2. The majority of current keyboards cannot.

[BeBuLamar]

Thanks! I still use IBM model M keyboards. In fact I tend to toss the keyboard that came with new computer.

[TechTaco]

As noted above with the Ardiuno, just to throw this out there, if you wanted to get even more compact a single PIC32 MX series chip could probably do this. It has USB support and the PS/2 keyboard protocol is quite basic which it can also do. The mouse protocol I'm not as familiar with.

The PIC32MX230F256B-50I/SP (~$5) DIP package for easy breadboarding, supports USB "On The Go" which allows a USB keyboard and mouse to be plugged in to the chip, as it acts as a host.

Chapter 12 of "Programming 32-bit Microcontrollers in C: Exploring the PIC32" by Lucio Di Jasio describes step-by-step how the PS/2 keyboard protocol works in depth and programming for it on the PIC32.