The PET Keyboard Expansion Project Page

Introduction

Welcome to the PET Keyboard Expansion Project Page! The PET keyboard is arranged as an 8x10 matrix, allowing 80 keys. When I started my PET Keyboard Replacement project I used a C64 keyboard. I saw that the PET used a 4-to-10 decoder chip, meaning it has 4 binary lines that get expanded to 10 individual lines that connect to the keyboard. Of course 4 lines can actually represent 16 different values (2^4 = 16) so it follows that I could replace the 4-to-10 decoder with a 4-to-16 decoder and expand the keyboard to 8x16 or 128 keys without affecting compatibiility with the existing 8x10 keyboards.

This project is to design a PCB that plugs into the existing VIA chip socket responsible for keyboard scanning. This PCB will contain the new 4-to-16 decoder and bring out all lines to a new keyboard connector, while leaving the original keyboard usable.

Schematics and PCB

Here is the current schematic diagram and PCB: