> This sort of goes back to what the intent is.  I don't really expect to
> see high frequency noise (but this may be way wrong on my part, of
> course).  What I wanted to smooth out was variations in crank rotational
> speed (if any) caused by the cylinders firing.  That might cause the
> readings displayed on the LCD to be unstable and/or inaccurate.  So I
> guess it's intended as a ripple filter and not a HF noise filter, though
> on reflection I may need both.

Having done something similar I'd recommend you do a software PLL (or
averaging) that integrates the pulses over a whole rotation of the shaft
(assuming you get many pulses per rotation). Machines with veriable load
and reciprocating machines have some higher order rotational vibration
components in the shaft which lead to misreadings if you use a two-sensor
approach (two sensors near each other to read a slow shaft).

Peter

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