[Magister]

For the moment I have a small switch to shutdown the gizmo before leaving the car, but each time I go into the car I have to switch it to on before starting the engine, and it's annoying.

I am testing an "ignition sense interface" (2 transistors, 2 diodes, 2 resistors) that will require a wire from the accessory (like the cigarette lighter).

The OBD2 plug always has the +12V even when there is no key in the contact. A pin will be used on the atmega as a "keepon".