The Robotpark MEGA ADK is a microcontroller board based on the ATmega2560. It has a USB host interface to connect with Android based phones, based on the MAX3421e IC. The Mega ADK is compatible with all of Android's Accessory Development Kit examples and also acts like the Mega. It has 54 digital input/output pins (of which 15 can be used as PWM outputs), 16 analog inputs, 4 UARTs (hardware serial ports), a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. You can connect any sort of sensor, LED, motor, etc to your Android based phones using Robotpark Mega ADK.
Schematic, Reference Design & Pin Mapping.
Schematic, Reference Design & Pin Mapping - Google's ADK documentation.