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'[EE]: IR object detection'
2002\08\24@142913 by Dale Botkin

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Hi all,

I'm looking at an object detection problem for which I want to use a
simple, cheap IR LED/phototransistor pair.  I plan to have each rigidly
mounted and aimed, say a meter or so apart, and can use a flat black
tubular shroud say half an inch to an inch in length at each end.  I could
probably also use an IR filter on one or both ends.  In an environment
with high ambient light levels, like outdoors, the sensor would either be
pointed downward or parallel to the ground.  Does this sound like it's got
a chance of working most or all fo the time, or is this doomed to fail if
used outdoors?  I'd hate to have to resort to using a 40kHz modulated
beam, and I'm not sure that it would make that much difference outdoors.
Who's been here already?  This is the first time I've looked at using IR
for a project like this.

Dale
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2002\08\24@153546 by Bob Blick

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> I'm looking at an object detection problem for which I want to use a
> simple, cheap IR LED/phototransistor pair.  I plan to have each rigidly
> mounted and aimed, say a meter or so apart, and can use a flat black
> tubular shroud say half an inch to an inch in length at each end.

Do you mean that the sensor and the emitter are a meter apart, or
there are two pairs, each pair very close together?

> used outdoors?  I'd hate to have to resort to using a 40kHz modulated
> beam, and I'm not sure that it would make that much difference outdoors.

You really have to modulate, or at least pulse and look for a pulse,
unless you can control the ambient conditions.

Also be aware that a phototransistor will not work beyond a certain
frequency(40khz is too fast). A photodiode is used in the
conventional 40khz modules.

And if you have the emitter and detector a meter apart, it's going to
be very hard to make it work outdoors.

Cheerful regards,

Bob

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2002\08\24@161552 by Dale Botkin

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On Sat, 24 Aug 2002, Bob Blick wrote:

> > I'm looking at an object detection problem for which I want to use a
> > simple, cheap IR LED/phototransistor pair.  I plan to have each rigidly
> > mounted and aimed, say a meter or so apart, and can use a flat black
> > tubular shroud say half an inch to an inch in length at each end.
>
> Do you mean that the sensor and the emitter are a meter apart, or
> there are two pairs, each pair very close together?

Sensor and emitter one to two meters apart.  Probably multiple pairs
separated by about six inches or so.  Of course I can stagger the pairs to
make that "look" farther apart like this:

E --> S

S <-- E

E --> S

> > used outdoors?  I'd hate to have to resort to using a 40kHz modulated
> > beam, and I'm not sure that it would make that much difference outdoors.
>
> You really have to modulate, or at least pulse and look for a pulse,
> unless you can control the ambient conditions.

Well, I just looked at what it would REALLY cost to do a 40kHz modulated
pair...  child's play, and cheap.  I thought the Sharp IR receivers were a
lot more expensive than that, but they're really cheap.  And I can use one
PWM output to drive all the emitters.

> And if you have the emitter and detector a meter apart, it's going to
> be very hard to make it work outdoors.

There are a lot of indoor applications for this, but outdoor applications
would significantly expand the possibilities.  Hmm.  Maybe longer
shrouding or something...  I'll have to do some playing around with this,
obviously.  Or it may be as simple as a sun shade over the whole mess,
which is not great but not unworkable.

Thanks for the response, any information I get at this point is a
plus!

Dale

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2002\08\24@161657 by PICLIST

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Hi Dale,
Check out www.rentron.com/Infrared_Remote_Control.htm.
I was able to send 1200 Baud serial comms at 100 ft indoors,
and 50 ft in sunlight. It's not exactly what you're
looking for but, it might give you some ideas. I just used
the circuit from Rentron, and a F628 for a 40Khz carrier wave.
The part I used was from Jameco #165008 Mfg Ref #SHARPGP1U26X   2.95 USD

Good Luck,
Kevin

{Quote hidden}

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2002\08\24@161707 by Jim

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I bought a Radio Shack Infrared Alarm unit a
few years ago - it's pre-built and has a relay
contact as output - and it works on my porch
(not direct sun, but indirect sunlight).

Comprised of a combo Sender/Rcvr and a special
"mirror" placed several to five feet away.

Break the beam and a contact closure occurs.

Size: about 8 x 6 x 4 inches.

More info if interested ...

RF Jim


{Original Message removed}

2002\08\24@164848 by Dwayne Reid

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Have a look at the 'firestick' at <http://www.rentron.com> - he gives schematics
and parts lists.  It does use 40 KHz modulated IR but the parts look cheap
and he achieves 200' operation.

dwayne

At 01:01 PM 8/24/02 -0500, Dale Botkin wrote:
{Quote hidden}

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2002\08\24@164853 by Dale Botkin

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On Sat, 24 Aug 2002 RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU wrote:

> Check out www.rentron.com/Infrared_Remote_Control.htm.
> I was able to send 1200 Baud serial comms at 100 ft indoors,
> and 50 ft in sunlight. It's not exactly what you're
> looking for but, it might give you some ideas.

It's close, and the especially useful part is that you were able to get it
to work over that range.  This is exactly the kind of information I was
looking for.  I can do the modulation and use a Sharp module to detect it,
and it's looking more like it will work OK.  I probably should have been
more clear in my original post, I'll just be using a few beams to detect
an object passing through.  THe only big difference is that instead of
using the modulated IR beam to transmit data, I'll just be using it to
detect the presence or absence of an object passing through the beam.

Thanks!

Dale

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2002\08\24@164911 by Dale Botkin

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On Sat, 24 Aug 2002, Jim wrote:

> I bought a Radio Shack Infrared Alarm unit a
> few years ago - it's pre-built and has a relay
> contact as output - and it works on my porch
> (not direct sun, but indirect sunlight).
>
> Comprised of a combo Sender/Rcvr and a special
> "mirror" placed several to five feet away.

Heh.  Now I'm getting ideas about physical mounting that I hadn't thought
of before.  Wonder if I can get this sort of arrangement to work with
pairs located a few inches apart?  Probably not, but I'll sure test it to
make sure.  8-)

I LOVE THIS LIST!

Dale

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2002\08\24@231911 by Nelson Hochberg

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In case your soldering iron is not working:
http://www.norcoalarms.com/ezStore123/DTProductList.asp?p=2_1_1_0_0_0_40

Nelson

{Original Message removed}

2002\08\25@003646 by Dale Botkin

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On Sat, 24 Aug 2002, Nelson Hochberg wrote:

> In case your soldering iron is not working:
> http://www.norcoalarms.com/ezStore123/DTProductList.asp?p=2_1_1_0_0_0_40

Ah, thanks, but this particular project will involve several sets mounted
at specific intervals in a small space.  Prebuilt commercial units aren't
an option for size and cost reasons.

Besides, I'm *NEVER* without a working iron...  I used to say my favorite
programming language is still solder, though C is catching up quick.  Now
I'm afraid C has overtaken solder, as I've come to believe the perfect
solution is one involving zero parts other than the PIC.  8-)

Dale

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2002\08\25@104509 by Anand Dhuru

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Hi Dale,

If you wany any degree of relaibility, I'm afraid you cannot really avoid
the 40 KHz (or thereabouts)  modulation. Having said that, I think the best
article that would guide you to do precisely what you want is at the
Parallax site at
http://www.parallaxinc.com/html_files/resources/wknd_specials.htm


{Original Message removed}

2002\08\26@104344 by Yura

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Hey, Dale !

Try to look here:
http://microtechnique.epfl.ch/isr/asl/systems/alice/Asensors.pdf


Best regards,
Yura                            RemoveMEyura_boyspamTakeThisOuTmail.ru

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