Getting Started with Arduino

Driving Bigger Loads (Motors, Lamps, and the Like)

Each one of the pins on an Arduino board can be used to power devices that use up to 20 milliamps: this is a very small amount of current, just enough to drive an LED. If you try to drive something like a motor, the pin will immediately stop working, and could potentially burn out the whole processor. To drive bigger loads like motors or incandescent lamps, we need to use an external component that can switch such things on and off and that is driven by an Arduino pin. One such device is called a MOSFET transistor—ignore the funny name—it's an electronic switch that can be driven by applying a voltage to one of its three pins, each of which is called a gate. It is something like the light switch that we use at home, where the action of a finger turning the light on and off is replaced by a pin on the Arduino board sending voltage to the gate of the MOSFET.

Note

MOSFET means "metal–oxide–semiconductor field-effect transistor." It's a special type of transistor that operates based on the field-effect principle. This means that electricity will flow though a piece of semiconductor material (between the Drain and Source pins) when a voltage is applied to the Gate pin. As the Gate is insulated from the rest through a layer of metal oxide, there is no current flowing from Arduino into the MOSFET, making it very simple to interface. They are ideal for switching on and off large loads at high frequencies.

In Figure 5-7, you can see how you ...