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'[PIC]: PIC IR Proximity Detector ?'
2001\12\20@234902 by kben

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Hi,
I am trying to build a PIC IR Proximity Detector, the bascic TX circuit
is figure 2 on this page >>>
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)
So, I thought if I add a digital pot instead of manually changing
the resistor,
I could make a rudimentary IR Proximity Detector.
Problem Digikey only sells a 10k digital pot, I was hoping to find a smaller

one,like <= 1k, anybody know where I could get one ?
Is their an easier way to do this with a PIC ?
I already looked at the Sharp GP2D02, but I wanted someting cheaper.

Thanks in advance,
                  Kevin

P.S. I am a programmer not an EE, so my electronics background is limited.

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2001\12\21@011552 by Jinx

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> one,like <= 1k, anybody know where I could get one ?

http://www.xicor.com/product_select_guide.php?table=xdcp

I saw 1k pots (quick glance), perhaps Xicor have lower values

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2001\12\21@012855 by PICLIST

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Hi tony,
I thought about that, but I quess, what I really want is better resolution,

IE 10k 8bit pot gives (10k/256) approx = 39ohms.
if I had a 1k digital pot it would be (1k/256) 3.9ohms.  This would allow
me to calculate distance more accurately.


>Less resistance is easy, just put in a parallel resistor.
>R_total=R_1*R_2/(R_1+R_2)
>Of course the output is no longer linear through the full range of the POT.

>
>tony
>
>{Original Message removed}

2001\12\21@014159 by Steve Faulkner

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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.

{Original Message removed}

2001\12\21@022442 by Roman Black

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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

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2001\12\21@050320 by Andrew Verhoeven

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I looked at a digital pots (Xicor and Dallas) a few years ago.  I didn't use
them because the wipers could handle very little current. If I'm right, you
will probably have to use a transitor after the Digital Pot - your required
resistance may change.  (DS1267)

regards,
Andrew





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2001\12\22@222019 by Steve Faulkner

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If you want to save some money, buy the GP2D12 - $13.50 at Acroname.. (in
fact, Acroname is the only company I can find that carries them). It is
cheaper because it has a voltage output rather than digital. This link is a
nice overview of why Triangulation IR sensors are the way to go and the
different types of Sharp models..
http://www.acroname.com/robotics/info/articles/sharp/sharp.html


{Original Message removed}

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