This project was created on 06/05/2015 and last updated 3 years ago.
Description
This project can translate the keystrokes from a PS/2 keyboard into equivalent switch closures of a matrix keyboard with 8 lines by 8 rows (the number of lines can be expanded, though).
It can be used to replace the or work in parallel with the original keyboard from classic computers, like ZX81/Spectrum, MSX, TRS-80, TRS-Color, Commodore 64, etc

This project is free, under the license CC by 4.0. See https://creativecommons.org/licenses/by/4.0/
Details
 
The circuit consists of a PIC16F688 microcontroller that reads the PS/2 keyboard and eight 74HC595 shift registers. Each key read rom a PS/2 keyboards is translated into a map of bits that are serially sent to the shift registers.
The current board has the following features:
Capable of emulating a 8x8 matrix expandable to 8 x n (board has already solder points with identification for that).
Three connectors for PS/2 Keyboard: Mini Din -6, 4 pin header and USB female (some keyboards can revert to PS/2 compatibility when they can't establish an USB connection).
2 I/O pins for reading special modifier keys or indicators (like caps lock, etc).
Serial 'Header' serial (TTL levels) for ease of debugging or for 'cross typing' (send pressed keys to serial and activate received characters - this is just a possibility and it's not implemented yet)
PIC ISP header for development and burning new firmware.