I'm very new to electronics, but am trying to build a device that should be attached to a motorcycle (Arduino based sensor board) which should only draw power when the engine is running; specifically given the finicky nature of motorcycle batteries, and that my device will have an approximate two ampere draw.
I've been researching comparator circuits, but it seems as I want to avoid any draw on the battery when the engine isn't running.
I have self-imposed restrictions on specifically not interfacing with any of the bike's other circuitry, mostly because it's brand new, and I don't want to splice/hack into any wiring that might relate to the safety electronics, etc, etc; I can rely on a connection to the battery, and I'm hoping to detect 12v±1v when the motor isn't running, and closer to 14v when the alternator is doing it's job.
I heard a quip that I could use an opamp and a zener to somehow boost a 3v button cell to a suitable reference voltage to drive the comparator, that I might compare against 13v, for example.
The missing puzzle (in spite of lots of time spent with Google) is how can I use a rechargeable (I expect) button cell at 3v to compare against a 12-14(±1)v input.
Assuming that I detect the battery is currently charging from the alternator, I'll be stepping the voltage down to 5v using a LM2569, which is closer to the button cell's voltage, but doesn't help me to avoid drawing on the battery when the motor isn't running.