You can use a reflective label on the prop, or just reading the light
intensity  difference through the prop. To improve that technique, just
attach to the prop a label half white, half black, so it will helps to
create a discrimination of light / dark even in different ambient light
conditions.

Wagner.

Brian Kraut wrote:
>
> I remember from my RC days that the commercial tachs for airplanes could be
> used a few inches away.  They also read light through the prop, not reflected
> from it.
>
> Geoff Child 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?
> >
> > Thanks
> >
> > ______________________________________________________
> > Get Your Private, Free Email at http://www.hotmail.com

--
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Wagner Lipnharski - UST Research Inc. - Orlando, Florida
Forum and microcontroller web site:  http://www.ustr.net
Microcontrollers Survey:  http://www.ustr.net/tellme.htm