An Everlight or Sharp 40Khz detector, when on frequency and
properly modulated, will give you 30 to 40 inches of
detection - depending on the object reflectivity. I've
gotten hits at over five feet before, but that certainly
wasn't very reliable and such a range is pretty useless on
my robots.  I usually tune the osc off frequency to get the
range down to less than a foot.  Since I wasn't trying for
long range, I would imagine that you could do a few things
to get it - like driving multiple LEDs, making sure they are
pumping at max current, focusing the beam, etc.

Be sure you shield the LEDs with foil. Ground the case of
the detector if you are using the Sharp module (already
grounded with the Everlight).

I've used the GP2D02 and there was just a discussion on it
on the SRS list. You need to ground the case of it for a
start.  The case is plastic, but it is conductive.  One
problem with it is its narrow beam - good for ranging, but
not for general object detection.  The other is that it
really requires a separate PIC or something to handle the
code overhead for triggering and shifting in the range
(IMHO).  Acroname was publishing PIC code for driving it -
look on their website and under the GP2D02 advertisement.

Range detection by signal strength with IR is not very
reliable unless the target is stable,  has known
reflectivity and has consistent shape.  Which is not the
case for any target I'm looking for.

The GP2D02 detectors have very good noise filtering, the
Everlight and Sharp 40 Khz detectors are OK. I have not seen
a homebrew filter that would compete - though I'm sure it
could be done with PLL control of some sort.

If you want to see a PIC driver for an IR detector using an
Everlight module, then I've made one using a 12C508/9 and it
is on my site at: http://204.233.101.40/robots/brb.html . It
was also in last month's Encoder at www.seattlerobotics.org
.


Finally, before venturing into long range IR, why not try
Sonar? I get very consistent results with the Polaroid sonar
pack and it works out to 35 feet and in to about 6-11
inches.  You can see one at www.acroname.com .

Good luck,

Dan
-----Original Message-----
From: Dwornik, Sebastian <SDwornik@CRSROBOTICS.COM>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Wednesday, August 25, 1999 8:16 AM
Subject: Signal filtering through code


>My current robotics project requires me to design and build
an accurate
>and stable IR proximity detection sensor system. It should
give feedback
>of objects up to 5 feet. My chosen tools are the PIC16F84,
the
>LTC1298 12-bit ADC, and the VTR24F1 optosensor from EG&G.
>The sensor simply contains an IR LED and a photodarlington
in a single
>package.
>
>My current solution involves simple noise filtering through
code. The
>opto proximity method is through the use of intensity or
signal
>strength,
>reflected off an object.
>
>Algorithm:
>        Pulse HIGH!     ; LED ON.
>        Read ADC        ; Result A = Signal + Noise
>
>        Pulse LOW!      ; LED OFF.
>        Read ADC        ; Result B = Noise
>
>        SUB A-B ; Result C = (Signal+Noise) - (Noise)
>
>        C = pure signal strength.
>
>This has proven to work well for distances up to 8 inches
using an 8-bit
>ADC. This is the first time I'm trying to extend the range,
with a more
>sensitive sensor and a 12-bit ADC.
>
>Is there a better algorithm of filtering which would
provide greater
>results? A better sensor, or maybe a better method to the
entire
>project. I have played with Sharps' GP2D02 module as well;
and have
>gotten rather unsatisfactory results. If the current method
cannot be
>improved upon, then my next step is to try one of those 40
khz
>Sharp IR modules. They won't give me proximity ranging, but
>maybe reliable object detection; and atleast that's a
start.
>
>
>Sebastian