I'm starting my PhD in Mechanical Engineering in September with a Controls concentration. I'm not at home for the summer as I have to take Senior Design to finish my undergraduate degree, and given the lack of things to do in my college town I was wondering what would be some good skills to work on and maybe have some fun with?

My initial idea was to spend some time learning to use an Arduino, but that also got me thinking about Raspberry Pi as well (not sure which would be more helpful to understand). I'm already an intermediate coder with Matlab/Python, as well as Autodesk/Catia/Solidworks (not sure if I'll even do that much CAD in controls phd though). Any thoughts?