At 11:37 PM 10/25/1999 -0500, you wrote:
>I am making a no contact tachometer using a pic for a model airplane and am
>trying to find a reflective sensor for the pickup. The ones that I have
>looked at have to be to close ~.150 inches and I would like to be several
>inches away. Does any one know of any any sensors?

Did one already.  You don't need to be reflective.  You can simply use a
photo diode (or an LED - somebody will explain how this works) to sense the
light.

The diode simply gets connected across an op amp, and voltage changes
according to light.

This is why, btw, things like the Tower tach tell you NOT to use them
indoors with flourescent lights.  They see the lights pulsing and report
THAT as the RPM (try it - it works!)

Ask private if you have any questions.  I can't share everything, but the
basic ideas are good.  You also want an AGC on the output (a cap &
resistor) to sense the changes.

Andy

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