> How clean of a source is the 12v stereo power supplied by a car?
> I've noticed it can vary from (in my car) 11.5v off the battery
> to almost 14v when the engine is running. I'm thinking that it's
> not a very well regulated source. So how likely is it that spikes
> and noise can make their way into the circuit being powered? The
> vehicle in question is a 1991 Geo Prizm (basically a Toyota
> Corolla of the same era).

        Generally power from cars are about the worst environment you can get in
to. Aside from the wide voltage swings, on the low end during starting, on
the high end during normal operation (even as high as 24V+ since that's what
might happen when a car gets boosted), the noise is huge. There are SO many
places for noise to come from after all. Aside from the obvious (injector
firing, spark flug firing), there is also noise produced by other systems
(i.e. ABS, the onboard computers, power windows and locks, etc.).

> I ask because I'm not sure what kind of protection might be
> needed in a circuit to be powered by such a source. If it's a
> significant problem, what can be done about it?

        Well generally a large amount of filtering is needed, along with wide
supply variation protection. TTYL

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