I did a little hardware hacking with the Raspberry Pi board. It has some GPIO pins on a connector that can be used for hardware expansion. I bought two low cost kits from AdaFruit that make it easier to use the GPIO port.
The Pi Cobbler kit provides a connector to the GPIO port and a ribbon cable that goes to a small breakout board that can plug into a solderless breadboard. It has all the pins nicely labelled. Below are a couple of pictures of my assembled board connected to a Raspberry Pi.
|Pi Cobbler Plugged in to a mini Solderless Breadboard|
|Pi Cobbler Connected to Raspberry Pi Driving an LED|
The Prototyping Pi Plate kit is a board which plugs onto the Raspberry Pi, similar to an Arduino Shield, that provides access to the GPIO pins via terminal blocks and provides a prototyping area for circuitry. I also purchased a mini solderless breadboard which can fit on the Pi Plate. A couple of pictures are shown below.
|Pi Plate Mounted on Raspberry Pi|
|Driving an LED|
Both kits went together easily in about 15 to 20 minutes with a little soldering. So far I have only had time to run simple programs to flash an LED driven by one of the GPIO lines (both shell script and C language versions). You can find lots of documentation and programming examples at this link.
I'm still waiting to receive my Gertboard, which is a more sophisticated input/output board for the Raspberry Pi that provides buffered input and output circuity and analog to digital and digital to analog converters. It also has an Arduino compatible chip on it.