The Paper-Duino-Pi is an Arduino shield for the Raspberry Pi. Due to the fact that it is designed as Paper-PCB it is easy to create and one doesn’t need a printed circuit board. All components are standard electronic parts that are easily available at your favorite electronic shop. Plus they are really cheap. All you need are some electronic knowledge and soldering skills.
One can use the Arduino IDE running on the Raspberry Pi to upload programs on the Paper-Duino-Pi. Once you uploaded the Firmata you have easy access to all the in- and outputs of the Arduino controlled by Pure Data, Python or Processing. This way it’s just simple to connect sensors, buttons and potis to control your program running on your Raspberry Pi. It also functions vice versa: connect light, motors, step- and servomotors and control them with the software running on the Raspberry Pi.
The board is designed with an 6.8kOhm resistor connected to 3,3V and the reset pin (of the Atmega chip) and a 4,7nF capacitor connected to the GPIO18 pin of the Raspberry Pi. It is possible to use the autoreset function with the GPIO18 instead the DTR line. A modification of the Arduino IDE and the avrdude that pull the pin 18 in the right moment do the trick.
Due to the fact that the Raspberry Pi runs on 3.3V the Serial Out (TX) of the Paper-Duino-Pi has a voltage divider. The Serial In on the Paper-Duino-Pi works with a 3.3V Serial Signal.
For more detail: PaperDuino Pi