For this final example, let's graduate from a simple DC motor control circuit to a hardware shield that can control one or two DC motors. For this example, you'll control two DC motors on a wheeled platform. There are several simple, two-wheeled robotic platforms; in this example, you'll use one that is available from several online electronics stores as shown in the following figure:

To make this wheeled robotic platform work, you need to control the two DC motors connected directly to the two wheels. You'll want to control both the direction and the speed of the two wheels to control the direction of the robot.

You'll do this with an Arduino shield designed for this purpose. There are several available; the shield you'll use here is the one available on the Arduino website at www.arduino.cc. The following figure shows the shield:

Specifically, you'll care most about the connections on the front corner of the shield, which is where you will connect the...