On Tuesday 15 July 2003 20:05, Alex Harford scribbled:
> > I don't have any links, but I do have a suggestion.  Someone suggeste=
d
> > a few weeks ago that monitoring the cigarette lighter voltage on a ca=
r
> > can be used to extrapolate the speed of the engine.  I don't know wha=
t
> > the relationship is; my suggestion, stick an o-scope on it and find o=
ut!
>
> Whoever proposed the idea probably figured that the voltage output woul=
d
> increase with increasing RPM.  In my experience, there are too many
> other factors that affect voltage (power windows, cooling fan,
> headlights) for that to be accurate.


BTW, a more accurate hokey idea for measuring RPM would be to measure=20
oil-pressure and have some proper temp compensation (actually measuring o=
il=20
temperature).  I am willing to bet it would be FAR more accurate than=20
measuring voltage, but I stress, it's still a hokey way to do things.

Cheers,
-Neil.

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