I just finished up my shield schematic for plugging into the Mega. I have a work in progress prototype using point-to-point soldering. I currently don't have the displays or bar graphs to test with yet, so I don't want to order just yet.

Here's a list of features it will have:

• 2 Joystick headers
• 8 I2C headers
  • For interfacing with LED barographs
• 1 SPI header
  • For interfacing with 7-segment displays (via daisy chain)
• 57 Data/5v/Ground Headers
  • 8 Analog In
  • 9 PWM
  • 40 Digitial IO
• 15 5v/3.3v/Ground Headers
• Reset header

This is probably overkill, but should allow maximum utilization of the Mega in case I decide to expand in the future. The data pins will all use extra long male headers, but the rest will use normal male headers.

I'm currently looking at using seeed to produce the PCB. Unfortunately 8x6.5cm is an odd size, so I have to go with 10x10cm which is $19/5 boards. If anyone's interested in buying a board, I'd be happy to split the order.

The Fritzing file is available on GitHub, but you can see a screenshot of the PCB in the project photos.