Arduino does many interesting things on its own, but it can’t do everything. Fortunately, thanks to the open design of Arduino, building add-on boards to extend what Arduino can do is pretty easy.
These boards are called “shields,” because they usually fit over the top of Arduino like a protecting shield.
Shields contain their own circuitry, components, and sometimes processing chips that can augment Arduino’s capabilities. There are shields that enable Arduino to read GPS signals, drive robot motors, take pictures, connect to Bluetooth devices, control electroluminescent wire…as of this writing, there are more than 300 shields. Keep up to date on shields at http://shieldlist.org.
In our opinion, the Ethernet shield (Figure 6-1 and Figure 6-2) is the most important Arduino shield, and the first one you should make or buy. Hooking your Arduino to an Ethernet connection can put it on the Internet, and once that’s done your options become nearly endless. Want to use your Arduino to set up a small web server? No problem. Place data online for other people to see? Simple. Send tweets via Twitter? Easy breezy!
Figure 6-1. Front of the Ethernet shield.
Figure 6-2. Back of the Ethernet shield.
Notice how the Ethernet shield is shaped very much like Arduino? ...