Introduction to Arduino - Arduino Sketches: Tools and Techniques for Programming Wizardry - page 21

having to make your own PCB. Prototyping on a breadboard is an excellent
way to test that your design works, but after the design is proven, it is time to
make a better board. For example, if you were creating a doorbell application, it
would be complicated to hide a breadboard behind the ringer. Instead, you could
solder those components onto a prototyping board, saving space and making
your design much more resistant to shock or tampering. The added advantage
of this type of board is that you do not need to create your own printed circuit
board or do any complicated routing.
The Diff erent Shields
Shields exist for a wide variety of applications: storage on SD cards, network
connectivity by Ethernet or WiFi robotics control, enabling displays like LCD
and TFT screens, to name but a few.
Most shields can be stacked, so you are not limited to using only one at a time.
However, some shields may require input and outputs that will subsequently
be unavailable to other designs. Be careful when you choose your shields!
Arduino Motor Shield
When using motors, special care has to be taken. When turned off, motors can
induce voltage spikes, and components need to be added to a design account
for this possibility. Also, typically, USB power is insufi cient for motors. The
Arduino Motor Shield takes care of this and enables the programmer indepen-
dent control of two DC motors, or one stepper motor. This shield can either be
powered from the Arduino or rely on an external power supply.
Arduino Wireless SD Shield
The Wireless SD shield is designed for an Xbee module but works with any
radio modem with the same footprint. The on-board micro-SD slot allows the
shield to act as a data logger. It also has a small prototyping area for adding
components.
Arduino Ethernet Shield
The Arduino Ethernet shield does exactly as the name implies; it adds
Ethernet connectivity through a W5100 controller, supporting up to four
simultaneous socket connections. This module also includes a micro-SD
slot for data-logging.
The Arduino Ethernet Shield has an optional POE module. On a POE
network, the module (and the parent Arduino) can be powered directly over
Ethernet.