I found a module that would be very useful, it has lots of digital inputs and most of all it has analog inputs witch will be good for a small motor that is used as a generator from the speedometer drive in the front wheel, then the volt (divided if needed) just needs to be converted to something like:
2.1V = 18km/h
2.8V = 24km/h

http://www.connectblue.com/products/...module-obs411/