Several people have asked about using MoPi for in-car Pi rigs. In this scenario we want the Pi to track the car ignition, and shut down cleanly after some housekeeping when the car is off, turning itself back on when the car is started again.
This requires a little extra circuitry:
Click through to the large version for more explanation.
Incidentally there are several other MoPi-related circuits on my CircuitLab workbench waiting for the 25-hour day to arrive. If you're scratching your head about how to hook the thing up in unusual scenarios that's a good place to look!
Motor on...