I have JRMI on my MacBook and communicating with the loconet through a Ditrax PR3. Is there any way that I can add a speedometer that can be read on my Android smartphone?
You would need to access the panel with the speedometer via a JMRI remote web panel. I do not believe WiThrottle/EngineDriver supports it. (And, of course, need the sensors, etc., configured properly with JMRI, but that is a different exercise). @Mark Watson has been using the Boulder Creek Engineering Roll-By speedometer, which couples with a smartphone. It works really well, and may be an easier alternative.
Thanks RGrodzinski. I have the RollBy transmitter that fits in a boxcar and wirelessly reports back to my Android smartphone. Works great.