At 03:38 PM 11/5/2009, you wrote:
><capav8r@gmail.com>
>
>Bob:
>
>Here is the circuit that is the current interface between the tach
>gen and the EFIS tach input. It was originally designed to
>interface a Hall sensor with a 10 V p-p input. The 50K resistor in
>parallel with the zener was to provide a current path (so I am told)
>should a p-lead be used instead of the Hall sensor.
>
>My thought was to put the circuit you have proposed in the location
>as shown in the attached document (I could not scan to a .jpg and
>the .bmp was way too big).
Okay. I think your 'trash' is coming from artifacts
on the wave-form that are a result of the combination
of the two phases of a 3-phase generator. These seem
to reside some millivolts away from ground . . . so
your results are bound to improve if you move your
comparator's decision-point as close to ground as
possible.
Try the simple transistor-zener circuit without
the comparator. The transistor's "decision point"
is in the .5 to .7 volt range as a function of
Vbe characteristics of b-e junction.
Bob . . .
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