> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of Brent Brown
> Sent: 10 October 2011 04:40
> To: Microcontroller discussion list - Public.
> Subject: [EE] Infrared proximity sensors
>=20
> I came across these sensors a few years ago while working on a project
to
> automatically sort cattle through automatic gates. These proved
excellent
> for
> sensing black cows (very low infrared reflectivity)... for example
other
> opto sensors
> we trialled would give a number of output pulses as a
Friesian/Holstein
> cow (black
> and white patches) walked past!
>=20
> http://sunxsensors.com/index.php?main_page=3Dindex&cPath=3D40_146
>=20
> They have several noteworthy characteristics as far as Infrared
diffuse
> reflective
> photoelectric sensors go:
> 1) Not affected by object colour or background
> 2) Adjustable distance (ignores objects beyond set distance),
mechanical
> adjuster
> not electrical
> 3) Large operating range (at least 2m)
>=20
> I would like to know how they work, instruction manual gives some
clues.
> From
> page 2 of manual, "Principle of fixed-focus sensing with 2-segment
> photodiode"
> "Normal reflective type sensors operate by sensing the variation in
the
> amount of
> incident beam. However, the fixed-focus reflective sensing type sensor
> incorporating the 2-segment photodiode operates by sensing the
variation
> in the
> incident beam angle. Thus, the output is activated according to the
> distance of the
> object from the sensor. This system helps the EQ-30 series in being
> unaffected by
> object color or a background, enabling stable sensing."
>=20
> I can perhaps visualise how 2 sensors help differentiate between near
and
> far
> objects. A lens (or even a pinhole?) might allow the incident beam
angle
> to hit one
> or both sensors depending on distance to object... I could be wrong
and/or
> there
> might be more to it than that. How would that help with object colour
> performance?

The Instruction manual PDF on then page you linked to has a very
simplified explanation.  AFAICT: ambient light, or a target outside the
operating range would cause both photodiodes to receive a similar amount
of light, but a target within the focal range will cause one detector to
receive more light than the other. By setting a threshold against the
ratio of the two photodiode currents rather than the absolute value,
variation in the total amount of light falling on the detectors will be
ignored (within the dynamic range of the sensors!), but it becomes
sensitive to the distance to the target.


Cheers

Mike

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
This e-mail is intended for the person it is addressed to only. The
information contained in it may be confidential and/or protected by
law. If you are not the intended recipient of this message, you must
not make any use of this information, or copy or show it to any
person. Please contact us immediately to tell us that you have
received this e-mail, and return the original to us. Any use,
forwarding, printing or copying of this message is strictly prohibited.
No part of this message can be considered a request for goods or
services.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.