Accessing the GPIO Pins - Arduino Robotic Projects - page 57

The GPIO capability of Arduino

Arduino was built to access the outside world. Much of that access is through the GPIO
pins. Each Arduino board has a different set of GPIO pins, so in this section, I'll provide
details on the GPIO pins available on the most common variant of Arduino: Arduino Uno.
Then, I'll also document the additional capability of the Arduino Mega. Finally, I'll show
the GPIO capability of a more limited Arduino: Arduino FLORA.

First, let's focus on the Arduino Uno. As described in Chapter 1 , Powering on Arduino , the
Arduino Uno comes with a set of 14 digital and six analog I/O pins, along with some addi-
tional pins to provide power and serial I/O.

Fortunately, the pins are actually well labeled on the board itself, as shown in the following
image:

The following table shows a list of pins that are available and a brief description of what
each pin can do, starting at the upper-right side of the board and going clockwise. A more
in-depth description of these pins will come later as you actually use them in some example
projects:

Arduino
Pin

Description

This pin provides a reference voltage for the analog inputs. The values on the analog pins will be reported in reference to this
voltage. You'll also use this in some applications to provide a reference voltage for some sensing devices. You can also provide an
external reference value to this pin, which means that the numerical values of the inputs will be scaled according to the value sup-
plied on this pin.

AREF

GND This pin provides a ground reference for the AREF pin.