Decoding 4x4 keypad with AVR and 74C922
Keypad decoding or scanning using microcontroller is, lets face it - nothing new. The thing is that sometimes it can be a real pain when smaller microcontroller with not enough I/O pins is being used or when microcontroller has some more important task to do besides scanning the keypad.
Anyway, here is a project that scans 4x4 keypad using Atmel's 4+4 I/O pins (the usual method) and by using a special IC designed for that purpose: MM74C922. This IC is directly connected to keypad rows and columns with it's 4+4=8 pins, and on it's 4 digital output BCD pins it provides information about which key is pressed on keypad. Along with those 4 data pins it also has IRQ pin that can generate interrupt in microcontroller when key press is detected. Keypad scanning has never been easier!
[ Source: nevdull ]