Why dont you use the Raspberry to control the shifters / Why do you need the Arduino?

The Raspberry PI has a small number of IO ports which could be used to control the shifters, which in theory could be used instead of the Arduino. When we started the project in 2012 the Raspberry project was still quite new, and there was not a lot of community information on how to use the IO features.

The Arduino project was however much more mature, and there were lots of example code for driving the shifters and community help forums if we needed help. For the £30 extra that the Arduino costs, the help and example code we got from the community was invaluable.