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'[OT] IR LED's That Produce a Beam'
1999\07\29@101652 by Martin McCormick

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       Thanks to all who responded.  The laser and mirror idea is
really neat.  The rest of you said that I should use a lens and
conventional IR diode.  I have both conventional IR diodes on hand
plus a few convex lenses left over from my past life as an audio
visual technician.  I was going to be lazy and use as few parts as
possible, but I will probably be much happier with the results using
the lens approach.  I was checking to see if I was missing anything
obvious before I got too far in to it.

       There are no PIC's yet with the only thing even close to logic
being the NE556 I will use to generate the 33 KHZ carrier and some
audio frequency around 400 or 500 HZ to gate the carrier because those
IR receiver modules don't work all that well with a steady carrier but
work very well when it is pulsed.

       One interesting problem I fully anticipate but haven't solved
is how best to handle the vertical component in tracking the beam.
In short, it doesn't matter as long as the beam is receivable.  I
could put a vertical row of LED's behind the lens, but that would
draw more current and probably not produce enough of a continuous slot
of light to be useful.  The other totally crazy idea I have is to take
a clear plastic rod a meter long or so and wrap it in paper or
aluminum foil except for a slot along one side.  The detector would go
at one end and hopefully, any light entering at right angles to the
rod would bounce around and come out the end.  Is this even possible?

       I have read some pretty far out postings at times on this list
so anybody who wants to laugh is welcome to do so, but we discuss
tracking ideas frequently and these are some of the basic things that
must be solved in order to successfully do the job.


Martin McCormick WB5AGZ  Stillwater, OK
OSU Center for Computing and Information Services Data Communications Group

1999\07\29@105841 by Wagner Lipnharski

picon face
> The other totally crazy idea I have is to take
> a clear plastic rod a meter long or so and wrap it in paper or
> aluminum foil except for a slot along one side.  The detector would go
> at one end and hopefully, any light entering at right angles to the
> rod would bounce around and come out the end.  Is this even possible?

Martin, the use of a lens in front of the receiver can works somehow as
a parallel beam filter, since if you position the sensor right in the
focus point from the direct IR rays.  The IR sensor is around 2 ro 3 sq
millimeter, while a small 20mm diameter lens is collecting and focusing
over the sensor.

Check this out:

A 3mm diameter sensor has only 7 square milimeters of area to receive
the IR.

A 20mm diameter lens concentrating focus over the sensor, has 314 square
millimeters of reception area, so your sensor would be 44.8 times more
sensitive.

A 30mm diameter lens increases the sensitivity in 100 times.

More important than everything is to colimate the transmit rays as much
parallel as possible, a narrow beam. If all the transmitter IR is
spotted over the receiver lens, you have 100% of energy transfered.
However, if the beam opens very few degrees and it projects a disc (at
the receiver plane) bigger than the receiver lens, so it will receive
less energy, the equation (aproximate) is this:

               ET
ER  =   ---------------------
        ( PDD / RLD ) ^ 2

ER = Energy Received
ET = Energy Transmitted
PDD = Projected Disk Diameter
RLD = Receiver Lens Diameter

better formula (I think):

       ET * (RLD/2)^2 * 3.14159
ER =    ----------------------------
         (PDD/2)^2 * 3.14159

that is the same as:

      ET * RLD * RLD
ER =  ---------------
        PDD * PDD


So, as much you could concentrate the IR beam, further you can receive
it, as much you could increase the size of the receiver lens, bigger the
sensitivity.

Hope this can help.
Wagner

1999\07\29@161921 by l.allen

picon face
>         One interesting problem I fully anticipate but haven't solved
> is how best to handle the vertical component in tracking the beam.
> In short, it doesn't matter as long as the beam is receivable.  I
> could put a vertical row of LED's behind the lens, but that would
> draw more current and probably not produce enough of a continuous slot
> of light to be useful.  The other totally crazy idea I have is to take
> a clear plastic rod a meter long or so and wrap it in paper or
> aluminum foil except for a slot along one side.  The detector would go
> at one end and hopefully, any light entering at right angles to the
> rod would bounce around and come out the end.  Is this even possible?
>
I have used an elongated triangular shaped piece of clear perspex
with one side diffused (sanded rough) and the detector (led shape)
inserted in a drilled hole at one end. This made a marvelous wide
target laser detector as the beam scattered when hit the diffused
side and the internal reflections would cause enough energy to
trigger the detector.
Lance Allen
Uni of Auckland
New Zealand

1999\07\29@191450 by Mike Keitz

picon face
On Thu, 29 Jul 1999 09:15:48 -0500 Martin McCormick
<spam_OUTmartinTakeThisOuTspamDC.CIS.OKSTATE.EDU> writes:
>       One interesting problem I fully anticipate but haven't solved
>is how best to handle the vertical component in tracking the beam.
>In short, it doesn't matter as long as the beam is receivable.

A cylindrical lens will concentrate the beam in one plane but allow it to
spread out in the other.  It sounds like this is what you want.  These
lenses are shaped like a half-cylinder.  They are stock items from Edmund
Scientific and similar places.

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