This adapter allows you to use Arduino shields or XBee modules on your Raspberry Pi. It also provides the ability to connect digital and analog sensors, using the same pinout as Arduino but with the power and capabilities of Raspberry Pi.
This connection bridge can be used on both Rev. 1 and Rev. 2 of the original Raspberry Pi model, as well as the B+ models and the Raspberry Pi 2 and Raspberry Pi 3 models.
To ensure compatibility, you can use the free arduPi library which allows you to use your Raspberry Pi with the same code used on an Arduino. To do so, the library implements conversion functions so that you can control all the I/O interfaces (I2C, SPI, UART, analog, digital) on the Raspberry Pi the same way as on an Arduino. See the user manual for details.
The picture to the right shows an older version of the Bridge. The image below shows the current design. This new version includes a Digital Switch to enable/disable the socket for wireless modules using GPIO23 (Digital Pin 3).
Raspberry Pi to Arduino Connection Bridge Resources