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'[PIC]:Using IR....determing position?'
2001\08\24@120730 by Micro Eng

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I am trying to decide if I can use an IR setup to determine if something is
in range.  I could use ultrasonic, but I wondered if IR might be easier.
All I want is PIC watching the inputs and if the box is moved within a
certain range (12"-16") turn on an LED.  Simple in concept....

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2001\08\24@174337 by Douglas Butler

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Are you intending to use the time it takes for the IR to reach the
target, or are you thinking of using the drop in amplitude with range?
The first will require very fast timing.  The second will mistake poor
visability or power variations for range changes.

Sherpa Doug

> {Original Message removed}

2001\08\24@192316 by Pedro Drummond

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I believe he just wants to check if the object is within 12 inches from the
source. Easy to do, by reflection of IR pulses. If the concern is regarding
the distance, 12 to 16 inches is ok. Just make sure you fire the IR LED with
high current, short time, for best results. You can use a PIC to do both
things: send a certain frequency of fires and check if the same pattern can
be detected back.




----- Original Message -----
From: Douglas Butler <.....dbutlerKILLspamspam@spam@IMETRIX.COM>
To: <PICLISTspamKILLspamMITVMA.MIT.EDU>
Sent: Friday, August 24, 2001 6:33 PM
Subject: Re: [PIC]:Using IR....determing position?


> Are you intending to use the time it takes for the IR to reach the
> target, or are you thinking of using the drop in amplitude with range?
> The first will require very fast timing.  The second will mistake poor
> visability or power variations for range changes.
>
> Sherpa Doug
>
> > {Original Message removed}

2001\08\24@220149 by myke predko

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Hiya,

I've implemented two proximity detectors with a PIC16C505 and I can offer
you a few comments about it.

1.  You will have to come up with a routine to pulse an IR LED at the
appropriate frequency while polling the IR Detector.  Not hard, but it will
take a bit of playing around.

2.  You will have to characterize the IR Detector that you are going to use.
I found some that will respond after two pulses, others will respond after
six or seven.  My code sends eight with the idea that if the object is in
range, the IR Detector will respond.

I then stop pulsing the LED for 1 msec because the IR Detector will continue
to be active for several hundred microseconds.

Your mileage may vary - decide on the IR Detector to use, characterize it
and don't change it.

3.  What is the object?  I found that this set up will have problems with
glass/mirrored surfaces if the reflected light is not directly pass the IR
LED output to the detector.  As well, rough black plastic will absorb the IR
signal and not reflect anything.

Anything in between these two extremes will probably be fine.

4.  You might want to put an opaque object between the IR LED and the IR
Detector.  I used the 47 uF caps that filter the power going into the IR
Detector.

5.  12"+ is somewhat extreme and you might have problems caused by
reflections on the flat surface your detector sits on.  If possible, you
might want to place it 6" or more above the surface to avoid the surface
from giving you false reflections.

6.  Instead of a straight current limiting resistor, use a pot (I used a
10K) and vary it until you have the sensitivity you want.  For my
application (a robot), I was looking for objects at 2" to 4", but just
trying the test rig out, I can detect objects 2' away.

7.  The sensor I came up with is pretty binary.  Don't expect it to be very
good at giving you any kind of distance measurement.


I have been working on a robot all summer that does collision detection
using this method and it is quite reliable, especially for the shorter
distances.  The big advantage of this method (along with reliability) is
that it is a very inexpensive way of implementing a proximity sensor.

Let me know and I'll pass along the test code I've developed.

I'll be putting the entire robot design up on my web page in the next three
weeks or so when the work crunch is finished.

myke

{Original Message removed}

2001\08\25@054247 by Ned Seith

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An infrared diode in conjunction with an infrared photo-transistor can
easily perform this reflective sensing task at a distance of 12" to 16".

The prepackaged infrared reflective sensors will probably not work at a
distance of 12".

Another possibility that I use is the TAOS (WWW.TAOSINC.COM) Light to
Frequency and Light to Voltage converters.
These light to V or F converters interface well with microcontrollers and
provide an output that is proportional and linear to the light or infrared
intensity received.
The TAOS light to V or F converters are available for ambient light
(300nm-700nm) sensing and infrared (800nm-1,100nm) sensing.
TAOS also has an evaluation kit that includes a microcontroller, LCD
display, ambient light sensor, infrared sensor and light sources.

Sincerely,
Ned Seith
Nedtronics
59 3rd Street
Gilroy, CA 95020
(408) 842-0858
.....nedKILLspamspam.....nedtron.com
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
At 10:06 AM 8/24/01 -0600, you wrote:
{Quote hidden}

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