I am aware that building an AVR can be accomplished with analogue components much more easily, but I want to proceed in this fashion (using a microcontroller) as a means to start off and get to grips with programming. It's my intention for the development of this to be an educational experience for myself, and as my understanding progresses I would like to be able to add and enhance it as time goes by. As alternators are relatively common (especially automotive ones) I thought it would make an ideal and low-risk first go. That is my primary motivation for using a microcontroller. I don't mind whether it succeeds or not, I just want to learn how to produce something that does a job and understand how it works.