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'[OT]: Laserdome'
2000\07\31@040416 by Marcus Johansson

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Hi!

I hear that the lasers used by lasertag games (aka Laserdome) are always
IR-lasers. Do they necessarily have to be that? Wouldn't it be possible
to use simple visible lasers such as the very cheap laser pointer,
available at only $10 or so? Could these lasers be pulsed at a frequency
high enough to provide the information necessary about the shooter?

Brgds,
Marcus

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2000\07\31@043739 by Quentin

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I guess it could be that visible laser can blind you and possibly damage
your eyes (anti-sue protection, etc.). I've never been to these but I've
seen pictures and they do wear protection.

Other thing I can think of is sensitivity of detectors to normal light.
It is easier to filter IR due to the higher wavelengths AFAIK.

Quentin

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2000\07\31@053648 by Michael Rigby-Jones

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All the laser tag games I have seen (commercial set-ups in warehouses etc,
not the ones you can buy from toyshops) use both an infra red laser and a
low power visible laser.  You need the visible laser to see where you are
shooting, but I guess the smoke and flashing lights these places have, cause
too much interferance to use the visible laser for carrying data, which is
why they use IR which can be filtered.

I've not seen anywhere in this country (UK) that makes you wear any kind of
eye protection, so I hope the lasers they use  are eye safe!

In response to the original question; yes, a laser diode such is used in
laser pointers can be modulated to produce quite high data rates (certainly
in the Mbit/s range) but unless you are guiding the light through fibre, you
will have a job to reliably detect and demodulate the data at the other end.

Paint ball is much better anyway...anticipation of pain is a good motivator
to move carefully and quietly :o)

Mike

> {Original Message removed}

2000\07\31@061425 by mike

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On Mon, 31 Jul 2000 10:35:56 +0200, you wrote:

>I guess it could be that visible laser can blind you and possibly damage
>your eyes (anti-sue protection, etc.). I've never been to these but I've
>seen pictures and they do wear protection.
>
>Other thing I can think of is sensitivity of detectors to normal light.
>It is easier to filter IR due to the higher wavelengths AFAIK.
>
>Quentin
IR lasers are more hazardous than visible ones at the same power, as
the eye will not blink to protect itself. It would certainly be a lot easier to detect an IR signal than a red
one as you can easily filter out all visible light.

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2000\07\31@074718 by Jinx
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> I've not seen anywhere in this country (UK) that makes you wear any
> kind of eye protection, so I hope the lasers they use  are eye safe!

Nor in NZ. I've serviced two tag set-ups (staff persistently incorrectly
charging the NiCd packs and customers dropping units and breaking
the diode assembly). Possibly the duty cycle (had a good poke about
to see how it all worked but  don't recall it), was low enough not to
contain enough energy to do eye damage. IIRC they were 10mW
TOLD9211 (?), Sanyo (?). They were about $100 each

> in the Mbit/s range) but unless you are guiding the light through fibre,
> you will have a job to reliably detect and demodulate the data at the
> other end.

Both systems I saw used jackets with nylon optical fibre spread around
them to catch the laser light. I haven't seen others but presume this is the
standard way. Work alright for those systems. Although the materials were
cheap enough, the system as a whole cost a packet. ETI (UK) did a
series about 3 years ago on how to make a tag game. AFAIR it was PIC-
based, as are a lot of their projects. Looked quite simple and
"professional"
quality, almost tempted. I may be wrong, but I believe that was a red laser
project

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2000\07\31@080134 by John A. Craft

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Yes, most off the shelf Laser diodes can be modulated enough to encode the
id of the shooter.  I have designed and produced a prototype set of Laser
Tag gear that only uses diodes at around 860nm at < 5mw.

Jc.

At 10:05 AM 7/31/00 +0200, you wrote:
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2000\07\31@193931 by Andrew

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Hi,

I worked in one "laser zone" in sydney, I maintained the guns... they simply
use the laser for show. The actual communication is via plain old IR leds.
They focus the led so that it has a few degree spread. you don't have to be
overly accurate to shoot your opponant. The guns I serviced had extra IR leds
on the sides which were used for communication back to a scor computer when
you walked througe the "Energizer room". they also used the extra leds to
communicate back to the opposition when they hit you so their gun would say
"good shot".... the visible laser was on a very short pulse less then a "safe"
dose if it happens to hit the eye.. I think it was about 250ms but I am not
sure of the exact number....

Andrew Thoms
--
    Software Engineer
    Fac Engineering
    University of Technology, Sydney
    No 1 Broadway, Broadway 2007
    NSW, Australia

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'[OT]: Laserdome'
2000\08\01@025227 by Marcus Johansson
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So an ordinary IR LED can actually reach the necessary 10-25 meters through smoke?
So we're actually talking about a strongy focused remote control? Of course, there
are IR LED's that can be pulsed with hundreds of milli-Amps so i guess that's the
answer... Am I right?

/Marcus

Andrew Thoms wrote:

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2000\08\01@204652 by Harold Hallikainen

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       I've heard that there was recently an article about modulating cheap
laser pointers with voice. Anyone have any ideas about modulating one
with high speed data as an "across the parking lot" LAN link?

Harold

On Mon, 31 Jul 2000 10:35:56 +0200 Quentin <qscspamKILLspamICON.CO.ZA> writes:
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2000\08\01@221922 by Dan Michaels

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Harold wrote:
>        I've heard that there was recently an article about modulating cheap
>laser pointers with voice. Anyone have any ideas about modulating one
>with high speed data as an "across the parking lot" LAN link?
>

Yes, I've heard they glue half-silvered mirrors to the inside
of tin cans, and bounce the laser beams off the mirrors, while
talking into the cans. On rainy/foggy days, they connect the cans
with string [sorry - my apologies - just couldn't resist].

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2000\08\02@032620 by Marcus Johansson

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I have been thinking about that aswell, it's pretty much like a megabit-range
laserdome isn't it :-) A standard laserpointer reaches some 100 meters I think,
and that would be enough for many purposes. However, it might be troublesome to
modulate that kind of devices with very high frequencies by just "turning the
button on and off". Has anybody reverse-engineered a pointer device like that?

/Marcus

Harold Hallikainen wrote:

{Quote hidden}

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2000\08\02@035403 by Michael Rigby-Jones

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> Harold Hallikainen wrote:
>
> >         I've heard that there was recently an article about modulating
> cheap
> > laser pointers with voice. Anyone have any ideas about modulating one
> > with high speed data as an "across the parking lot" LAN link?
> >
>
>
> {Original Message removed}

2000\08\02@092154 by M. Adam Davis

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The difficulty with cheap laser pointers is the power supply is not meant to be
modulated.  The changes in power supply are very slow to actually come out of
the laser.

You'd need to take the diode and build your own power supply/laser modulator.

There is a project which does this for serial cables somewhere on the WWW.
Getting a 10Mbit LAN going across one of these is likely to need more care and
consideration.

-Adam

Harold Hallikainen wrote:
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2000\08\02@093955 by James Paul

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All,

I don't agree with this 100%.  I have modulated a laser pointer beam
sufficiently enough to transfer music across the room.  Granted, it
wasn't CD quality, but for a voice link or low BW data, it would be
fine I believe.  What I done is went to Radio Shack and bought a
small transistor output transformer (~$2.00 IIRC),  wired the 8 ohm
side to my signal, and the 2000 ohm side to the laser pointer.  I
then used a photodiode to receive the modulated light, rectified it,
and fed it to a small amplifier.  Again, not CD quality, but I did
get intelligible results.  This was a quick and dirty rigup to see
if it would work at all.  With a little bit of refinement, I'm sure
you could get maybe a BW of ~200kbits/sec.  This may not be enough
for your application, but you probably could devise a different
modulation method, and get the BW higher.  The better method may be
as suggested below by removing/modifying the diode and associated
circuitry, and going from there.   If you get the BW much higher,
I'd be interested in knowing what you did.  And I'm sure others
would be too.   BTW, it might be beneficial to try this with more
than one different kind/mfg laser pointer.  The one I used was an
El Cheapo I picked up at Sams or Fiesta or some such.  I think it
cost around $7.00 or so.  Anyway, good luck and let us know how
you come out.

                                        Regards,

                                          Jim




On Wed, 02 August 2000, "M. Adam Davis" wrote:

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2000\08\02@111722 by vehasmaa

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Michael Rigby-Jones wrote:
>
> > Harold Hallikainen wrote:
> >
> > >         I've heard that there was recently an article about modulating
> > cheap
> > > laser pointers with voice. Anyone have any ideas about modulating one
> > > with high speed data as an "across the parking lot" LAN link?
> > >
> >
> >
> > {Original Message removed}

2000\08\02@113027 by M. Adam Davis

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TCP errors would be corrected, UDP errors may be detected, but there is no
error-correcting defined in the protocol.

I can see someone running PPP over a laser, it does have built in error
detection and correction (limited, but better than nothing)

-Adam

Jurva-Markus Vehasmaa wrote:
{Quote hidden}

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2000\08\02@113440 by Marcus Johansson

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This thread went from a lasertag-game just carrying the killer id to the
discussion of high-bandwidth laser links :-)

/Marcus

Jurva-Markus Vehasmaa wrote:

{Quote hidden}

> > > {Original Message removed}

2000\08\02@120600 by Arthur Brown

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This is called Hi-jacking and thr subject line should be changed.<g>
----- Original Message -----
From: "Marcus Johansson" <macceEraseMEspam.....ENEA.SE>
To: <EraseMEPICLISTspamMITVMA.MIT.EDU>
Sent: Wednesday, August 02, 2000 4:35 PM
Subject: Re: [OT]: Laserdome


{Quote hidden}

modulating
> > > > cheap
> > > > > laser pointers with voice. Anyone have any ideas about modulating
one
> > > > > with high speed data as an "across the parking lot" LAN link?
> > > > >
> > > >
> > > >
> > > > {Original Message removed}

2000\08\02@183125 by Peter L. Peres

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>Yes, I've heard they glue half-silvered mirrors to the inside
>of tin cans, and bounce the laser beams off the mirrors, while
>talking into the cans. On rainy/foggy days, they connect the cans
>with string [sorry - my apologies - just couldn't resist].

Actually I know of one ancient project that used a headphone speaker
(bared, dome painted with silver paint), to act as a light modulator and
send voice across great (100 metres, using telescope optics) distances.
The light was halogen 12V 20W, with mostly IR used (filters). I do not see
why a laser could not be used in the same way, with direct AM modulation.
Receiver was ac coupled LDR + LM386 style amp and phones.

Peter

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2000\08\02@183129 by Peter L. Peres

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>high speed laser modulation

I have gone to 38400 Bps using lasers and detectors stripped from CD
player laser units. The receive amp was a venerable uA733 used at max gain
(x100) followed by a 393 comparator. Optics were 1/2 binocular (3x10
theatre type I think). The far side was a catadiopter affixed at some 60
feet. Both Tx and Rx used binocular halves (of the same unmodified
binocular). The binocular I used had UNCOATED lenses and no IR filter.
Obviously.

Interface to PC using RS232 and homebrew test program (direct register
access serial driver etc written in C). The test program did bit stuffing
(detector threshold was automatic AC type) and made sure that the laser
was on at most 1/2 of the time. The lasers I tried were 60 mA dc so I ran
them at ~250 mA peak (with ~50% silence and 50% max duty cycle). I think
that I achieved some 10E-4 error rate after serious tinkering, and then I
gave up. Pointing a IR laser manually without helper devices across 60
meters is not something you want to do in a profession you make your
living out of imho. It used to work best in absolute darkness (night + any
streetlamps removed from the FOV).

Peter

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2000\08\02@203433 by Jinx

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> Actually I know of one ancient project that used a headphone speaker
> (bared, dome painted with silver paint), to act as a light modulator

Isn't window vibration / reflected laser used as a bugging method or
is that Hollywood stuff ?

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2000\08\03@025955 by Marcus Johansson

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Yes, it has been used (and still probably is).

/Marcus

Jinx wrote:

> > Actually I know of one ancient project that used a headphone speaker
> > (bared, dome painted with silver paint), to act as a light modulator
>
> Isn't window vibration / reflected laser used as a bugging method or
> is that Hollywood stuff ?
>
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2000\08\03@060732 by Alan B. Pearce

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>Of course the snag with this scheme is the accuracy you need in aligning the
>TX and RX, and keeping them aligned.  Rain, snow and mist/fog would also
>affect the system quite badly, as would birds/insects flying through the
>beam.  That could be solved, or at least reduced by using some form of error

reminds me of the story about someone who installed a light beam door minder in
his shop. One day it just buzzed continuously, no matter what he tried to stop
it. Eventually it was found that a spider had set up home right in the warmth of
the light beam!

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2000\08\03@064747 by Snail Instruments

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>I have been thinking about that aswell, it's pretty much like a megabit-range
>laserdome isn't it :-) A standard laserpointer reaches some 100 meters I
think,
>and that would be enough for many purposes. However, it might be
troublesome to
>modulate that kind of devices with very high frequencies by just "turning the
>button on and off". Has anybody reverse-engineered a pointer device like
that?

Hi Markus,

I have gained a good amount of knowledge about laser diodes from the
following site. Certainly worth reading.

http://plop.phys.cwru.edu/repairfaq/sam/laserdio.htm

Josef

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2000\08\03@071117 by Vasile Surducan

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On Thu, 3 Aug 2000, Snail Instruments wrote:

> >I have been thinking about that aswell, it's pretty much like a megabit-range
> >laserdome isn't it :-) A standard laserpointer reaches some 100 meters I
> think,
> >and that would be enough for many purposes. However, it might be
> troublesome to
> >modulate that kind of devices with very high frequencies by just "turning the
> >button on and off". Has anybody reverse-engineered a pointer device like
> that?
>
 The standard laser pointer curently sell on the market, have about 2.5
mW radiation power, tipical wave lenght 640...650 nm and can be easily
modulated up to 10KHz with a standard npn transistor. Also may be suplied
up to 9V (standard is 3V) but laser diodes is ageing quickly.

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2000\08\03@074622 by Andrew Kunz

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I modulate them at 38kHz (30% duty) with no problem, but I remove the feedback
portion and run them off a 5V cap discharged through an NPN.

Andy









Vasile Surducan <RemoveMEvasileEraseMEspamEraseMEL30.ITIM-CJ.RO> on 08/03/2000 06:16:18 AM

Please respond to pic microcontroller discussion list <RemoveMEPICLISTspam_OUTspamKILLspamMITVMA.MIT.EDU>








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cc:      (bcc: Andrew Kunz/TDI_NOTES)



Subject: Re: [OT]: Laserdome








On Thu, 3 Aug 2000, Snail Instruments wrote:

> >I have been thinking about that aswell, it's pretty much like a megabit-range
> >laserdome isn't it :-) A standard laserpointer reaches some 100 meters I
> think,
> >and that would be enough for many purposes. However, it might be
> troublesome to
> >modulate that kind of devices with very high frequencies by just "turning the
> >button on and off". Has anybody reverse-engineered a pointer device like
> that?
>
 The standard laser pointer curently sell on the market, have about 2.5
mW radiation power, tipical wave lenght 640...650 nm and can be easily
modulated up to 10KHz with a standard npn transistor. Also may be suplied
up to 9V (standard is 3V) but laser diodes is ageing quickly.

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2000\08\03@080323 by Michael Rigby-Jones

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To improve data rates you may want to look at using a pre-bias circuit.  The
pre bias could feasably use the existing laser driver.  It purpose is to
keep the current through the diode at some point past threshold.  The
modulation circuitry will effectively add more current.  The back facet
monitor built into the laser should be included as part of the feedback
circuit to the pre-bias to ensure the average power remains constant.  The
feedback will have to be suitably filtered to ensure that the loop only
reponds to average power.  With suitable components and lasers this
technique works up to 10Gb/s :o)

Mike

> {Original Message removed}

2000\08\03@163650 by Peter L. Peres

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>Isn't window vibration / reflected laser used as a bugging method or
>is that Hollywood stuff ?

You can buy sets like that over the internet using your credit card if you
feel suicidal, I think. They come with an attached Echelon file about you
;)

Afaik 'proper' laser scatter bounce eavesdropping involves SHF AM
modulation of the beam and using the Doppler effect of the moving target
on the beam to recover vibration data. There are other ways probably (the
above assumes an unhelpful target). But then I don't know much about these
things. I hope that the difficulties of modulating a laser at SHF are high
enough to make wannabee spies fail early (let alone receive that signal).

Peter

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2000\08\03@170121 by Dan Michaels

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Peter Peres wrote:
>>Isn't window vibration / reflected laser used as a bugging method or
>>is that Hollywood stuff ?
>
>You can buy sets like that over the internet using your credit card if you
>feel suicidal, I think. They come with an attached Echelon file about you
>;)
>

Here's a couple of links regarding Echelon, in case someone hasn't
heard of it [but don't accept any cookies]:

www.wired.com/news/politics/0,1283,15295,00.html
http://www.magnet.ch/serendipity/hermetic/crypto/echelon/echelon.htm


...........
>things. I hope that the difficulties of modulating a laser at SHF are high
>enough to make wannabee spies fail early (let alone receive that signal).
>

This is why engineering schools were invented.

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