The Gameduino 2 shield is plugged into the Arduino Uno R3.
A simple MIDI OUT circuit is created by connecting Arduino pin 3, 4 and GND to a female MIDI DIN socket via a 330 Ohm resistor.
The software "sketch" running on the Arduino displays a user interface on the Gameduino 2 touch screen, and touch input from the touchscreen is converted to MIDI commands which are sent to the attached synthesizer via the MIDI interface.
The system is powered through the Arduino's 5V USB connection, or can be powered via the Arduino VIn socket (7 to 12V).
Pics: all the different screens, MIDI connection circuit, link to video.
Patch select screen: