Authors: Mark Stanley, Alexander Brevig
The Keypad library is designed for driving matrix style keypads (matrix decoder) when using the Arduino platform. It uses the standard method of selecting a column and scanning all the rows to see which key may be pressed. Support is provided for various size keypads (or matrix style keyboards) up to 160 keys with a maximum of 16 columns and 10 rows. You can expand beyond that if you are willing to make minor changes to the library.
Features of this library are: Allows multiple, simultaneous, keypresses. (Current max of 10 keys at one time.) Backwards compatible with previous single-key methods. Has a built-in state-machine to debounce the keys without slowing down your code.
Online Wokwi Arduino Simulation link here: https://wokwi.com/arduino/projects/284084336653763080 Use this link to play with the keypad source code
Version 3.2 2015-08-17 - Tim Trzepacz: Added "stated" event listener that also receives key state as a parameter.
You can get more information about matrix keypads and how to connect them to your Arduino on the playground:
http://arduino.cc/playground/Code/Keypad
The source and file structure has been modified to conform to the newer 1.5r2 library specification and is not compatible with legacy IDE's.
For these IDE's, visit the link above to grab the pre 1.0 compatible version, or download it directly here: [pre 1.0 version].