The combination of Arduino, such as the Uno with the ATmel ATmega 328P, and the Raspberry Pi is a natural one. The RPi is an allround computer with I/O facilities and a general purpose, though not real-time, operating system. The Arduino is a programmable microcomputer with also lots of I/O including lots of digital I/O, analog inputs and PWM outputs, made for running a dedicated program with precise real-time performance. Where bitbanging I/O on the RPi is not such a good idea, on the Arduino on the contrary it is common. Exchange data via the serial ports to let both platforms enhance each other and work together.
I have two boards that add an Arduino experience to the Raspberry Pi: the RasPiO® Duino and the GertDuino. Both function well. The RasPiO® Duino is a simpler, better supported, better designed and cheaper solution, though you have to solder it yourself. The GertDuino is ready to run, more powerful, since it has two ATmega IC’s (a replaceable 328 in DIP and a 48) but a bit rough on details.
I prefer the RasPiO® Duino. £14 including postage worldwide.. Much better supported and designed, runs on all RPi models and on jessie. The GertDuino, €30, is a nice, build, and powerful board, Arduino compatible, two ATmega’s, with RTC and IRda, but takes away more of the RPi GPIO like I2C, and is a bit rough to work with and with much less support, the Reset issue, the board space wasted for a non-functional and not present powersupply, and seems to have problems on RPi model 2 and on jessie. Read More