As most seasoned Arduino users will know, there are two hardware interrupts available on digital pins two and three. However with the correct coding you can also have pin-change interrupts on other pins as well. They can detect a (i.e. be triggered) on a rising or falling state of the pin involved.To make this possible Lex Talionis has written his arduino-pinchangeint library specifically for the task. At the time of writing it works with boards that use the ATmega168 and '328 microcontrollers such as the Ardino Duemilanove, Uno, Freetronics Eleven, KitTen, EtherTen and more.
If you often work with barebones or non-board Arduino microcontroller projects - you'll appreciate our new Arduino pinout microcontroller labels: