DIY electronic shifting
If you want Di2 on your bike, but you don’t have an extra few thousand dollars burning a hole in your pocket, Computer Engineer Nabil Tewolde has a perfect solution for you. His DIY electronic shifting system is, for the most part, made from parts found at his local hardware store, electronics shop, and hobby shop. Sure it could use a bit of refinement from an aesthetic standpoint, but Nabil points out that this electronic derailleur was part of a larger project to build the ultimate bicycle computer, which you canread about on his blog.
He has posted an Instructable and thre is more, read the article at bicycledesign