The RasPiO Duino is a small plug-on board that has functionality similar to that of an Arduino, but is programmable from the Raspberry Pi. Once it has been programmed it can be removed from the Pi and used on its own, or can be used interactively with the Pi. There is a 72-point prototyping area and the Pi's GPIO ports are also broken out onto the Duino.
All the ports on the Duino are clearly labelled. Each of the useful pins on the ATmega are broken out to a cluster of three holes. Male and female headers are provided, so you can connect whatever you like to your RasPiO Duino.
The Duino comes as a kit and will take about 30 minutes to build, with some soldering required. Once you have built it, software programming should take another 15 minutes and then you are ready to go. For programming, there are three jumpers to connect the microcontroller’s SCLK, MISO and MOSI directly to the Pi’s corresponding pins. For two-way serial communication with the Pi, if you need it, you can add two more jumpers to connect the Pi and ATmega’s Rx and Tx serial ports. RasPiO Duino uses the ATmega 328P-PU which is the same microcontroller chip as both Arduino Uno and Gertboard. It has a 6 channel analog to digital converter (ADC) and 14 digital I/O pins, 6 of which can also be used for PWM.
To make things easier, and to get lots of information on the Duino an excellent full user guide and Arduino programming instruction manual has been produced:
"Learn Arduino Programming with RasPiO Duino"
This book contains all the information you need to get into Arduino programming on the pi, such as:
Brief technical information
A brief build guide (with links to in-depth assembly instructions)
Comprehensive software installation instructions
Lots of example sketches and walk-throughs showing how to use the capabilities of the board
Links to the RasPiO Duino github repository
An easy-install script for the sketches
High-quality diagrams and photographs
47 Pages of educational inspiration, discovery and fun
Low cost, easy introduction to Arduino programming on the Raspberry Pi