Now that you are familiar with the Arduino IDE and how to create, edit, and upload a program, this chapter will now turn your focus to the HW. You'll get a chance to learn how to connect to and access the capabilities of the general purpose input/output (GPIO) pins from the SW. In this chapter, I'll start by explaining the GPIO pins, what they can and can't do, and then show you how to make Arduino access the outside world with the help of some very basic circuits and very simple programming examples.