We released the Pi 
Co-op, an Arduino add-on board for the Raspberry Pi back in the middle of January. But for various reasons, we haven’t had the time to do much promotional work, and explain to people why it’s so cool, and why you’d actually want to add an Arduino to your Pi.
To fix that, we’ve created a video, because reading text can be really boring 
, and then, we’ve written this blog post to show you one of the really useful things you can do with the Pi Co-op. We show you how you can use your Pi Co-op as a general purpose I/O board for the Pi.
So now, instead of having to buy loads of different add-on boards for your Pi, you can just buy the Pi Co-op here. You can use it as an Analog to Digital Converter (ADC), you can use it to connect to 5V devices, you can use it to generate PWM signals, and you can use it for I2C. To top it all off, you can also control all of this functionality from a high level language such as Python.