At the Google IO Conference in May, the Android team unveiled a few exciting features for connecting Android devices to the external world. USB Host capability, for instance, gives a device the ability to power and connect to USB input devices such as keyboards, mice, and joystick controllers. USB Accessory support, by contrast, allows the Android device to behave as an Accessory, so that another device can be the Host. This will allow you to plug your Android device in to a piece of hardware and communicate with real-world components like sensors, motors, etc.
At IO, they also demonstrated (and gave away) the Android Development Kit, or ADK. This is an Arduino Mega board with a USB Host chip as well as an Android Demo Shield, designed by Google to demonstrate a variety of inputs and outputs. For inputs the board has 3 pushbuttons, an analog joystick, a capacitive touch sensor, a light sensor and a temperature sensor. Outputs include RGB LEDs, relays, and some custom servo outputs.
When I went to Maker Faire in late May, I managed to get my hands on one of the ADK kits. Unfortunately my phone is stuck waiting for the long upgrade cycle of Samsung and AT&T, so it’s still on version 2.2, and doesn’t support accessory mode.