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'[EE] Multiple IR transmitters for better coverage?'
2016\10\17@135824 by Neil

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Hi all,

I've got short time to finish up an IR TX/RX system for a Maker Faire project.  I'm having some issues getting my IR comms to work reliably due to distance and angle.

Briefly, I'll have a 4' x 6' playfield with an IR LED mounted centrally 44 inches vertically above the field.  Small cars can be anywhere on the field and need to receive commands from that IR emitter.  I've calculated that max angle is about 41 deg, and distance between transmitter and emitter is 60 inches at that point.

IR comms works fine up to about a 30+ deg angle, so I'm considering 2 emitters transmitting exactly the same thing at the same time. Would I have any issues with this?  And anyone have experience on if it would be better to have both emitters at the same point, pointed about 20-30 deg apart, or should I space the sensors a couple feet apart, so each one covers half the field.


Cheers,
-Neil.

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2016\10\17@144740 by Josh Koffman

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On Mon, Oct 17, 2016 at 1:58 PM, Neil <spam_OUTpicdude3TakeThisOuTspamnarwani.org> wrote:
<snip>
> IR comms works fine up to about a 30+ deg angle, so I'm considering 2
> emitters transmitting exactly the same thing at the same time. Would I
> have any issues with this?  And anyone have experience on if it would be
> better to have both emitters at the same point, pointed about 20-30 deg
> apart, or should I space the sensors a couple feet apart, so each one
> covers half the field.

Hi Neil,

There definitely used to be TV/VCR remotes with multiple IR LEDs in
them. Given the speed of light I'm not sure you'd have phasing issues
if the sources weren't close together, but if you can get the coverage
you need with a small array all in one location, won't that make
building it easier too?

Josh
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2016\10\17@145830 by Van Horn, David

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More transmitters driven at the same moment is better.  No phase issues, the wavelength around 800nm You could bounce them off the ceiling of the room for more dispersion.
{Original Message removed}

2016\10\17@150723 by Harold Hallikainen

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We make an IR panel with about 100 LEDs in it. The LEDs are modulated with
three RF carriers (1.8MHz FSK, 2.3MHz FM, and 2.8MHz FM). The IR panel is
mounted on the back wall of a movie theater. The IR is reflected by the
screen at the other end (up to 30 meters away) and covers the auditorium.
We also allow for the use of slave panels. I suggest these be mounted at
the same location and just be used to get more IR power or to increase the
radiation angle. I have had people put panels in the four corners of a
room with coax between them. The delays in the coax result in the RF
modulation cancelling in some locations in the room. I visited one theater
that had trouble getting coverage in the middle of the room with four
panels. We put one at the back of the room and got rid of the problem.

In your situation, I see no problem with multiple LEDs to spread the
radiation angle. Further, since the modulating frequency is pretty low,
distance between them should not have any effect. You may be able to just
hang more LEDs in series (our panels have multiple series strings of LEDs
with each string driven by a current source).

Good luck!

Harold



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2016\10\17@151032 by Neil

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Hi Josh,

Was not aware of remotes that had multiple LEDs.  Considering the low data-rate I don't expect issues, but perhaps there's something I'm not thinking of here.
The emitters have a 90-deg angle, and the IR receivers also have a specific receive angle (also 90 deg).  Splitting the emitters apart will keep the receiver's angle lower, and is not really much more work to do.
But I'm also considering multiple emitters all together, but raised higher to reduce the angle to the cars.

This blog has more info on the whole setup...
https://teejaydubblog.wordpress.com/

Cheers,
-Neil.



On 10/17/2016 2:47 PM, Josh Koffman wrote:
> Hi Neil,
>
> There definitely used to be TV/VCR remotes with multiple IR LEDs in
> them. Given the speed of light I'm not sure you'd have phasing issues
> if the sources weren't close together, but if you can get the coverage
> you need with a small array all in one location, won't that make
> building it easier too?
>
> Josh

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2016\10\17@162451 by Sean Breheny

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Another reason that you don't have phase issues is that the LEDs are not
coherent sources. If you had laser diodes as your sources you COULD have
phase issues, although if the lasers are not phase-locked they would likely
drift enough relative to each other that the interference pattern would
change much faster than the data rate.

On Mon, Oct 17, 2016 at 3:10 PM, Neil <.....picdude3KILLspamspam@spam@narwani.org> wrote:

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2016\10\17@224949 by Neil

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The ceiling is an unknown, and may be very high.  But I can raise the emitters a couple feet higher to reduce the angular difference. I'll find out for sure on Frida, and also find out if there are any really bright lights I need to worry about.

Thanks,
-Neil..




On 10/17/2016 2:58 PM, Van Horn, David wrote:
> More transmitters driven at the same moment is better.  No phase issues, the wavelength around 800nm
> You could bounce them off the ceiling of the room for more dispersion.
>
>

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2016\10\17@230424 by Neil

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Good to know, thanks.  I'm running these off a microcontroller with a transistor driver, so I've got enough drive capability to put them in parallel.

Curious -- if you're allowed to say -- what do these huge emitters control?  Since you mention movie theater, are you broadcasting audio or some other effects?

Cheers,
-Neil.



On 10/17/2016 3:07 PM, Harold Hallikainen wrote:
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2016\10\18@002838 by Harold Hallikainen

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Neil,

If you have enough voltage, it's easier to put the LEDs in series which
puts the same current through each.

The emitter is shown at
www.uslinc.com/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=44&category_id=21&option=com_virtuemart&Itemid=106
.. It carries hearing impaired audio, visually impaired audio, and closed
captions in movie theaters.

Harold



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2016\10\18@012027 by Neil

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I will be powering this from a 6V wall-wart with a 5V, 500mA switching converter.  I have a bunch of 9V wall warts laying around, but that's not much better.

Yes series is easier, but I don't have much overhead voltage to work with.  Other than just needing more resistors, is there a benefit to series for this usage?

Cheers,
-Neil.


On 10/18/2016 12:28 AM, Harold Hallikainen wrote:
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2016\10\18@020040 by Bob Blick

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Hi Neil,

IR LEDs have really low Vf, something like 1.1 volts at continuous rated current, and probably still pretty low at high, pulsed current. You could easily use them in series pairs.

Cheers, Bob
________________________________________
From: piclist-bouncesspamKILLspammit.edu <.....piclist-bouncesKILLspamspam.....mit.edu> on behalf of Neil <EraseMEpicdude3spam_OUTspamTakeThisOuTnarwani.org>
Sent: Monday, October 17, 2016 10:20 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Multiple IR transmitters for better coverage?

I will be powering this from a 6V wall-wart with a 5V, 500mA switching
converter.  I have a bunch of 9V wall warts laying around, but that's
not much better.

Yes series is easier, but I don't have much overhead voltage to work
with.  Other than just needing more resistors, is there a benefit to
series for this usage?

Cheers,
-Neil.


On 10/18/2016 12:28 AM, Harold Hallikainen wrote:
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2016\10\18@021002 by James Cameron

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You would use less resistors per LED if they were in series, and less
power loss in the resistor, but it will depend on the forward voltage
of your LEDs as to how many you can use in either your 9V, 6V, or 5V
configuration.

Parallel would use more resistors per LED, with more power
loss per resistor, but does bring the advantage of the array
continuing to operate if a LED or resistor fails open.

However, parallel supply to LEDs that are in different places means
more cabling is exposed for short circuit failure.

I think the main advantage of series LED strings is that you have a
greater certainty for the current in each string, and if the current
limiting element is expensive (e.g. a switching regulator in constant
current configuration) you get to have less of them per LED.

If I were you, for this demo, I'd be fine with resistors per LED.

On Tue, Oct 18, 2016 at 01:20:26AM -0400, Neil wrote:
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2016\10\18@105558 by Denny Esterline

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Bright lights isn't usually a problem. Lots of IR (sunlight, incandescent
bulbs) or lots of light with a frequency component (early CFL, some LED
bulbs) are often an issue. (I know - that doesn't leave many options ...
:-) )

I have a specific lamp in my family room that must be turned off to use the
remote controls for the TV, etc. Somewhere on my list of "get around to it"
I was planning on setting up a receiver and examining the output of the
bulb just to satisfy my curiosity. I suspect that it's internal switch mode
converter is hitting a harmonic of the remote's modulation frequency.

On Mon, Oct 17, 2016 at 7:49 PM, Neil <picdude3spamspam_OUTnarwani.org> wrote:

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2016\10\24@161521 by Neil

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Reporting back...

The multiple emitters worked beautifully.  I used 4 in all, and they worked great, so I separated them by a couple feet and I saw no change or degradation in performance.  The receivers picked up the signal from the next booth's table too.

Much thanks,
-Neil.




On 10/18/2016 1:20 AM, Neil wrote:
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2016\10\24@233327 by RussellMc

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On 18 October 2016 at 08:24, Sean Breheny <@spam@shb7KILLspamspamcornell.edu> wrote:

> Another reason that you don't have phase issues is that the LEDs are not
> coherent sources. If you had laser diodes as your sources you COULD have
> phase issues, although if the lasers are not phase-locked they would likely
> drift enough relative to each other that the interference pattern would
> change much faster than the data rate.
>
>
​LEDs have proven better for optical comms than LASERs due to interference
of multi-path coherent light ​

​from a single emitter.

A single emitter tends to be nicely phase locked to itself :=_
​
​I'm somewhat surprised at the short range here - it may very much be a
lack of path than attenuation. As others have noted, scattering from a
distance may halp - you may be able to tower" mount a scatterer and point
the emitter upwards' at it. ​I've been surprised in the past how well
optical transmission works in a scattering environment - such as a room
(mainly simple remotes and a little low speed data so nothing too
demanding).


​Russell
​
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2016\10\25@091059 by Van Horn, David

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Ceiling bounce worked well when I was looking into this for connecting point of sale devices.  Unfortunately we couldn’t assure any reasonable optical path in that environment. In the end, hardwired cables won out.


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2016\10\25@102907 by Harold Hallikainen

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As mentioned before, we shoot IR from the back of a cinema auditorium
towards the screen where it is scattered to cover the entire auditorium.
In a series of tests, we mounted the IR panel at the back of the Fremont
Theater (
www.kcet.org/shows/artbound/the-many-lives-of-the-fremont-theater
) and reflected the IR off the screen. We could receive the IR signal at
each of the approximately 850 seats in the house. The distance from the
emitter to the screen is about 125 feet (40 meters). The IR carries 3 RF
carriers (1.8 MHz FSK, 2.3 MHz FM, and 2.8 MHz FM). The IR emitter and
receivers are shown at
www.uslinc.com/index.php?option=com_virtuemart&Itemid=72&vmcchk=1&Itemid=72
..

These systems are used to carry closed captioning, hearing impaired audio,
and visually impaired audio (also called "Audio Description" where there
is a voice describing what is happening on the screen). An advantage to IR
is that it covers the auditorium but does not leak into other auditoriums.
Some competing systems use RF instead of IR. There is currently a lawsuit
where complainants say the equipment at a theater was unreliable. In one
situation listed in the complaint, the user finally got a receiver that
worked. But, instead of getting Audio Description for the movie she wanted
to see (The Imitation Game), she got audio description for "Fifty Shades
of Gray."

Harold


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2016\10\25@113814 by Sean Breheny

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hahahaha

On Tue, Oct 25, 2016 at 10:28 AM, Harold Hallikainen <
KILLspamharoldKILLspamspammai.hallikainen.org> wrote:

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2016\10\25@120256 by Van Horn, David

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VBG!   Yup, RF sucks in some applications.  Even inductive loop systems would have some leakage.
Still, I don't understand people like this.  Part of living in a free society is being exposed to things you don't like.  But, that's another tag.
I do understand being annoyed at the wrong audio program.  You'd think that they would change frequencies so adjacent theaters wouldn't crosstalk.

Back when I did alarms, (disco days) we settled on infrared, as all the other ultrasonic and microwave, and RF technologies penetrated walls and couldn't be controlled.
Passive IR (thermal band, 10 microns) doesn't go through glass or walls in any significant way.

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2016\10\25@150011 by Denny Esterline

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>
> VBG!   Yup, RF sucks in some applications.  Even inductive loop systems
> would have some leakage.
> Still, I don't understand people like this.  Part of living in a free
> society is being exposed to things you don't like.



Interesting - I believe I interpreted this differently than you suggest.
I assumed that they _were_ on different frequencies or otherwise isolated,
but in the process of getting one that didn't work and having an employee
exchange it (possibly multiple times) the customer inadvertently received
one that was intended for a different theater.

-Denny
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2016\10\25@151117 by Van Horn, David

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That may be.  
-----Original Message-----
From: RemoveMEpiclist-bouncesTakeThisOuTspammit.edu [spamBeGonepiclist-bouncesspamBeGonespammit.edu] On Behalf Of Denny Esterline
Sent: Tuesday, October 25, 2016 1:00 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Multiple IR transmitters for better coverage?

>
> VBG!   Yup, RF sucks in some applications.  Even inductive loop systems
> would have some leakage.
> Still, I don't understand people like this.  Part of living in a free
> society is being exposed to things you don't like.



Interesting - I believe I interpreted this differently than you suggest.
I assumed that they _were_ on different frequencies or otherwise isolated, but in the process of getting one that didn't work and having an employee exchange it (possibly multiple times) the customer inadvertently received one that was intended for a different theater.

-Denny
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