Keyboard Matrix Help

Dave Dribin

v1.1 24 Jun, 2000

Revision History
Revision 1.124 Jun, 2000Revised by: dd
Converted to DocBook SGML and updated diode information.
Revision 1.04 Feb, 1999Revised by: dd
Initial release.

Attempts to explain how a keyboard matrix works, what "ghosting" and "masking" are, and how to prevent them.

Table of Contents
1. Introduction
2. The Matrix Circuit
3. Scanning to Detect Key Presses
4. Single Key Presses
5. Multiple Key Presses
6. Three Simultaneous Key Presses and Ghosting
7. The Masking Problem
8. Getting Rid Of Ghosting and Masking
9. What Diode Parts to Use
10. Conclusion

1. Introduction

It took me a bit to figure this out, partly due to the fact of no really good explanation of it. So, I'm going to have a crack at it. Basically, I wanted to understand how keyboard matrices work. Specifically, I wanted to know why keyboard "ghosting" and "masking" happen, and how to prevent them.

This article is 1999-2000 Dave Dribin. This article may be reproduced in whole or in part, without fee, subject to the following restrictions: