Steve Faulkner wrote:
>
> Using an IR photo detector you are going to get a LOT of variance in your
> distance readings depending on what the light is reflecting off of.  A
> "triangulation IR" detector like the GP2D02 will be *much* more stable and
> consistent in it's measurement, because it actually triangulates the
> reflection - like a laser range-finder.

Absolutely correct. :o) I have made some IR "table
edge" sensors for small robot and the detection
was up to 10cm with white paper and 5mm with a matte
black surface. They are JUST usable for table edge
on/off sensors but no good for ranging, you need
triangulation as the reflectivity of the surface
has such a huge effect on signal strength.

One system is to use one transmit led and two
receive diodes, in a black box so that as the target
gets further the angle changes and one receiver gets
less reflected light but the other always gets full
light. Hopefully it will be easy to find distance
by measuring the difference between the two sensor
voltages. It will require a modulated light source
and receivers that will detect AC infrared and give
a voltage based on signal strength, input into two
PIC AD inputs.

My preferred way would be to adjust amplitude to
the transmit led by PWM, so that the "control"
receiver gets fixed at a set signal strength coming
back, so then the signal detected at the other receiver
is always proportional to distance.
-Roman

> > I am trying to build a PIC IR Proximity Detector, the bascic TX circuit
> > is figure 2 on this page >>>
> > http://www.rentron.com/Infrared_Remote_Control.htm
> > If I add a small resistor (10-330 ohms) between the IR led and gnd,
> > it changes the distance the RX circuit detects a reflection from
> > (10cm -120cm)

> > Thanks in advance,
> >                    Kevin
> >
> > P.S. I am a programmer not an EE, so my electronics background is limited.

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