An Arduino shield is an add-on circuit board designed to work with the connectors on a standard Arduino board like an, Uno, Mega, Duemilanove, or Leonardo. A shield has pins that interface with the Arduino so that things like DC Power, digital I/O, analog I/O, and so on are available to the shield. Shields are available for a variety of application, ranging from minimal boards for prototyping to motor controllers, Ethernet interfaces, SD flash memory, and displays. Many shields have the ability to be stacked, allowing a base Arduino board to interface with two or more shields at once.
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