Tact switches are widely used as digital input devices. Normally one tact switch requires one digital I/P pin of a microcontroller but if you want to interface a matrix of such switches (say a 16 digit keypad), assigning a digital I/O pin for each key won’t be a good idea. You need to think about the way to minimize the required number of digital I/O pins of microcontroller. A very popular method is a keypad matrix where the keys are arranged into rows and columns so that a 4×4 (16) tact switches can be interfaced to a microcontroller using only 4+4 = 8 I/O pins. [via]
Theory of Matrix Keypad – [Link]
A matrix keypad uses rows and column arrangement of keys to reduce the required number of I/O pins for interfacing with a microcontroller. This article shows how you can use a 555 Timer IC to interface a keypad with just 2 connections. The 555 timer is configured in astable multivibrator where the output frequency changes with each key press. Based on how many times the Timer module overflows, the information about the pressed key is determined.
2-Wire Keypad Interface with a 555 Timer – [Link]
In this instructable I will show you how to build a quite fancy 8 by 10 L.E.D matrix(with scrolling text and animations) using the Arduino and 4017 decade counter. This type of matrix is easy to make and program and it is a good way learn how to multiplex.
Make a 8×10 L.E.D Matrix – [Link]
After making a 8X10 matrix a lot of people asked me about expanding the matrix to some thing bigger, and some wanted to write stuff to the matrix via a PC, so one day I looked at a pile of LEDs that I had leftover from a LED cube projected and I decided to make a bigger matrix with all the things people wanted.
So what are you waiting for? Get those LEDs out and heat up your soldering iron because we are about to make a 24X6 LED matrix!
Make a 24X6 LED matrix – [Link]
Fabien Royer writes:
As part of a netduino hacking tutorial that I’m authoring with my friend Bertrand, I wrote a set of classes designed to drive an 8×8 LED matrix relying on persistence of vision.
Driving an 8×8 LED matrix with a netduino using persistence of vision – [Link]
This project shows how to build a 5×8 LED matrix controlled by Arduino and placed on a Jacket. View details on the link below.
Arduino Lilypad – 5×8 LED Jacket – [Link]
Recently, I tested the 0832 LED Matrix Board that I purchased from Sure Electronics. Since I have a simple AVR microcontroller breakout board and a PIR sensor that senses motion, I decided to make something fun using the 0832 LED Matrix Board.
Motion Activated Message Display – [Link]
The LoL Shield for Arduino is a charlieplexed LED matrix for the Arduino. All the LEDs are individually addressable, so you can use it to display anything in a 9×14 grid. Scroll text, play games, display images, or whatever else you want with the Lots of LEDs shield.
LoL (Lots of LEDs) Shield for Arduino – [Link]