Raspberry pi expansion system page
If you want to hook up your raspberry pi to interface with the rest of the world, this is the right place to look!
The rpi_serial board is the simplest breakout board for the Raspberry pi.
It breaks out the following serial buses:
As the rasberrypi runs at 3.3V IO signal levels, the board allows 5V peripherals to be connected. The board can be configured for 5V operation or for 3.3V operation but not both.