As I announced, recently I've started to sell "Minimal and self-contained ATmega1284P "mod chip" at tindie.com ( https://www.tindie.com/products/microwavemont/minimal-and-self-contained-atmega1284p-mod-chip/ ) and here I would show one example of wonderful application of ATmega1284.
Actually this schematic is same as presented by [Dan] in several years ago, which can be found at single chip AVR basic computer, but some of the code (including several libraries) does not work at current Arduino IDE (1.6.10) and I rewrite them and released at github ( https://github.com/kodera2t/minimal1284 )
For PS/2 connector connection, please confirm by yourself by reliable data source. For example,this figure is wrong (5V and GND is reversed) and your keyboard may be destroyed ( actually I did break my keyboard by this connection.)
Actual operation can be found in the following movie.Please enjoy them!