Sorry, forgot to quote the message i was responding to...Like I said the way
to
determine the rpm is by reading the ignition noise off of the 12v line, not
the alternator
noise.

Mike Hillpot


>
> I've never heard of this, but I suspect that the problem will be getting any
> kind of sizable signal. The presumption is that the AC output of the
> alternator will put pulsations on the battery bus, but the amplitude
> is unpredictable. You will have to determine empirically the relation
> between the pulsation frequency and the RPM. Also, ignition noise will
> have to be dealt with, since it may occur at a different mutiple of the
> RPM. If there is a signal, the processing sequence would
> be filtering, amplification, and extraction. For extraction, I would use
> a phase locked loop. No FFT should be necessary.
>
> John Power
>
> --
>


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