Landmarks on the Arduino Diecimila board

Beside the USB port, also on the left side of the Arduino, is a black power outlet socket. Although the Arduino draws its power from the USB port when it’s plugged in, it can also be powered through any AC adapter, which plugs into the wall outlet socket, and outputs +5 volts of DC power. Moving from left to right, you’ll notice there are a number of discrete components, and then a series of small LED lights. These are connected to some of the more commonly-used features on the board, including two connected to pins 0 and 1 to show serial communications (to show when the Arduino is transmitting data to and from the computer), and another LED connected to pin 13 (usually used to debug circuits, but more on that later).

In the middle of the Arduino is a large black integrated circuit (IC). This is the ATmega 168 chip that runs the Arduino. The ATmega 168 is the “brains” of the microcontroller board, and it communicates with the rest of the board. Next to this chip is a reset switch. When this switch is pressed, the Arduino temporarily resets itself, and then restarts whatever program is loaded onto it at the time.

Finally, and perhaps most importantly, are two rows of black “headers”. These tall, elevated headers are digital input and ouputs signal pins. Some of the pins are also connected to analog inputs, and to power and ground signals. These headers serve two purposes. First, they are the perfect size for wires, which can connect the Arduino to other circuits. For the purposes of this book, and most of its projects, however, these headers are where other modules (sometimes called “shields”) are inserted onto the Arduino. By inserting a module on top of the Arduino, the Arduino’s functionality is expanded.