Modulation/demodulation of Red & Green laser pointer and laser sensor

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How to modulate laser pointer
=====================
I want to modulate a Red and Green laser pointer (laser diode) with audio
sweep signal 1-10KHz square wave with adjustable duty cycle.
For the modulation I'm planning to use a simple transistor circuit where the
base of the transistor will be conneced to a signal generator and the laser
pointer will be connected to the collector of the transistor. The transistor
will be used to switch on/off the laser diode.

How to sweep the modulation signal and rotate the laser pointer
===========================================
Signal generator will sweep the frequency from 1KHz to 10KHz in 1second.
During this 1 second period laser pointer will be physically rotated from  0
degree to 180 degree (From Left to Right). Then signal generator will  sweep
the signal from 10KHz down to 1KHz and laser pointer will be rotated from
180 degree to 0 degree (From Right to Left).

Laser receiver sensor
===============
There will be a receiver/sensor on an arbitrary position at a distance of
100meters (or more). When the laser light hits the sensor, I want to detect
the laser signal and demodulate the received signal. The frequency of the
demodulated signal will indicate the angle of the receiver/sensor with
repect to the laser pointer.

Questions
=======
 1.) Can you advise a good way of modulating the laser pointer?
 2.) What can I use as receiver sensor which can operate even in daylight?
 3.) Can you advise a good way of demodulating/decoding the received signal?
 4.) Would it make any difference if I use either Red or Green laser
pointers?

Thx.

Rahgu






Re: Modulation/demodulation of Red & Green laser pointer and laser sensor



<Rahgu Seghar> wrote in message
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It might be sufficient to use an audio O/P transformer with the O/P winding
in series with the laser supply, but if you're using proper current limited
feeds this probably won't work! It may be better to use a coupling cap to
the base of the current regulator transistor.



Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


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Direct pulse modulation is easiest.  A mosfet or bipolar transistor will
do.
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A silicon pin photodiode would be sensible.  You don't state the range
you need.   A narrow band interference filter at the laser wavelength
in front of the diode will greatly reduce the effect of sunlight.

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I'd use a carrier in the 100khz to 1 mhz range (fixed frequency) so it
would be easy to easy to filter out low frequency noise.  THen you can
audio modulate the signal.  Rather than using tone you could send the
angular positon as pulse coded data whhich is likley to yield better
angular resolution vs time than an angule vs  frequency scheme. I'm
assuming you have a miroprocessor on both ends

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Red will have a little less solar interference, better sensitivity for
silicon detectors, and much lower cost for a given power level laser and
have less absorbtion by the atmosphere.  Infrared in the 800 to 950 nm
range would do better still in all respects.


Re: Modulation/demodulation of Red & Green laser pointer and laser sensor



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In fact, if you get the absolutely dirt cheapest Far East import red
laser pointers, they have no regulator and no filter caps (just a current
limiting resistor) so directly controlling power will be able to modulate
from DC up to many MHz.

Better ones will have some sort of filter capacitors on the power and
modulating at more than a few Hz may not be possible without going inside.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
 Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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        | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
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Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


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How far will a such reach on a clear summerday outdoors ..?
(detected by some photodiode to off/on state)


Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


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what do you mean, current limiting resistor? thats included in the
battery....

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most of the not-ultra-cheap (ie laser + battery) pointers I have
dismembered have had lasers with monitor photodiodes, and a crude
control loop: npn drives laser, PD goes to base of pnp with pulldown,
pnp emitter to battery, collector to npn base. the pnp then controls the
laser intensity (in theory. best not to think about accuracy .)

(too lazy to draw sch).

an open-collector transistor will happily OOK the laser, if connected to
npn base.

Cheers
Terry

Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


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I was surprised they'd only use a resistor, however Sam knows his stuff
so I assume he's run across them.

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<snip>

This has been my experience as well. I've taken apart maybe 20 of them
over the years, and they all had a control board with a MOB or SOIC chip
on them. I would imagine it's possible that some of the later versions
could have the control circuit on the laser die itself. Some of these
wholesale for sixty cents each, with a couple of holographic filters,
case, and battery, so they must be manufactured for about 5-10 cents.

-- Gordon

Re: Modulation/demodulation of Red & Green laser pointer and laser sensor



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:)

Yep, I've seen lots of them but never actually bought one myself.  I can
tell no one is surprised. ;-)

Apparently they were available for awhile at Dollar Stores.  These typically
came with multiple pattern heads.  They have also been given away as
freebies at conferences and trade shows.  Really crappy construction,
just hold together well enough to work for a short time.

See:

http://www.repairfaq.org/sam/slasptr.jpg

I don't see the surface mount 50 ohm resistor so it must be underneath
the PCB.

Interestingly, the laser diodes used in these have a much
wider operating current range (lower slope efficiency) than
the typical high quality devices which almost have to use
some type of optical feedback to deal with a wide
temperature range and differences between devices.  The ultra
cheapies can be safely driven like LEDs.  Perhaps crappier Far East
manufacturing techniques have an advantage or maybe specifically
designed that way.

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Those are the ones above.

The older red pointers had discrete parts; some newer ones have an IC,
others still use discrete parts.  There are several circuits in:

http://www.repairfaq.org/sam/laserdps.htm

I've never seen any with control on the laser diode chip.
For one thing, it's not practical to implement circuitry on the
GaAs-whatever material, so there would have to be a separate
silicon chip.  Not worth it for the volumes involved.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
 Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
        | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line.  Or, you can contact me via the Feedback Form in the FAQs.

Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


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Hmmm.  No doubt it's a laser substrate, but I'd question if it's really
lasing. If one doesn't care about actually making the material lase,
these have quite a wide latitude for current input. The beam will still
be "laser-like" to the average consumer.

Have you tested these pointers to see if they are operating in true
lasing range? If they are, they've figured out how to do something
pretty nifty with laser diodes: operate them without a current mirror or
other feedback!

-- Gordon

Re: Modulation/demodulation of Red & Green laser pointer and laser sensor



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Yep, no doubt it's a laser.  There's a distinct threshold, the speckle
is present, they can probably output 10 mW with a very well collimated
beam, and all for something that costs 10 cents to make.  These do not
just look like a laser. :)

I should have noted that it's not just that one can't find a regulator,
varying the input voltage does have a major effect on output power.

I think what they figured out is how to make a really mediocre laser
diode with low slope efficiency.  And from what I've heard, these
things are not very reliable in the long term, partially due no doubt
to the exposed die with no protection, but possibly also a result of
material impurities.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
 Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
        | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line.  Or, you can contact me via the Feedback Form in the FAQs.

Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


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<other good responses snipped>

Curiously, this poster has the same posting headers as "Rico Maxle," who
asked about long distance IR and collimation a few weeks ago. The end
application of this *still* sounds to me suspiciously like an
Opticon-buster.

-- Gordon

Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


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In a free society each citizen has the right to learn and understand how
technology work and a moral and legal responsabilty to use his knowledge
safely and within the limits of decency and legality.  Any technology
can be used for good or evil.  Horrid as an "Opticon-buster" (whatever
that is) might be, having knowledge of how it works is not illegal or
immoral.  I've been well trained in now to kill people by the US Army
paid for by your tax dollars.  Is that knowledge evil?  Only if I misuse
it, which I don't.










Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


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Sure, it's a free society. I just thought it was interesting the same
guy has (apparently) posted with different names, and never seems to
really indicate what the project is about.

-- Gordon

Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


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What's a Opticon-buster ..?


Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


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An "Opticon-buster" is a device that emits modulated light for the
purpose of affecting traffic signals. They're illegal except for fire
and police...and dangerous for other drivers, because it causes the
lights to change out of sequence. In any case, a penlight laser does not
have the power output to trigger an Opticon at 100 meters. I guess with
very careful alignment and a very good receiver circuit and optics you
could capture and decode modulated signals at 100 meters, during the
day. Otherwise...

Of course, maybe the OP has something different planned, but it should
would be nice to have some additional information, like "I want to build
a...". Makes for better answers, if nothing else.

-- Gordon

Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


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System of traffic bypass controlled by laser is only used in usa ..?
(I think in europe it's through radio)

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It almost appals me that systems like this won't have even basic crypto.
Even just sending a static code (like remotes) would improve it :)

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Well people can always abuse technology..


Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


snipped-for-privacy@spamnuke.ludd.luthdelete.se.invalid wrote in news:447247fe$0$491
$ snipped-for-privacy@news.luth.se:

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I understand there are systems like this, using infrared with a
modulated code. The hacker then stands on the corner near a fire
station with their universal remote set on 'learn' and waits.
After a fire truck goes by they now have the coded pattern. All
that's necessary is modding the remote with a higher output. Now
they have a remote control for the traffic signals. :)


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Every technology is "dual use".

Brian
--
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Seismic FAQ: http://www.skywise711.com/SeismicFAQ/SeismicFAQ.html
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Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


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It's usually a strobe, but the cops can see these -- the strobe flashes
as a warning for people, and the IR content triggers the preemptive
controller. The all-IR models that are for sale in the US (where it's
illegal) are invisible. There are plans all over the Internet on how to
build one.

Frankly, I don't think a laser or other narrow beam would do much good,
and in thinking more about this, it's probably NOT the OP's intention.
There's no way it could be aimed accurately in a moving car.

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The later systems do have a more sophisticated modulation than the
originals. You have to remember this stuff has been around a long time
-- the 1960s for some of them. Kinda like how the music industry never
saw PCs coming, and the ability to record CDs...

-- Gordon

Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


Actually, Sony had a digital data scheme way back when CDs first got
started.  I've seen the specs for audio, digital storage and mixed mode of
digital data and audio on a disk.  There were some CD players that didn't
know about data disks but that nonsense was soon only on obselete CD
players.  Company I was working for at the time was the first outside of the
major players in the digital data field that made a mixed mode CD.  The
process was a bit involved but in the end, we got a glass master disk from a
place in the LA area.

--
Why do penguins walk so  far to get to their nesting grounds?



Re: Modulation/demodulation of Red & Green laser pointer and laser sensor


snipped-for-privacy@nethere.com:

<Snipola>
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Would that have been DMI? (Disc Mastering Incorporated) I worked
for them for a while in the late 90's in various positions,
eventually ending up wearing a bunny suit in the mastering department.

One of the mastering machines I got to play with was the first one
to ever master a disc in the US. Took up a whole 4x8 isolation
table and a pair of full height racks full of equipment. Although
we had other more modern equipment which was only half the size of
a fridge, this one was still used for those special discs that
weren't spec, like those that crammed 85 minutes of music on a
disc. We could manually control all the important parameters like
track pitch, bit rate, etc...

Then there was the DVD mastering machine...the one with the UV laser
so you couldn't see a damned thing on it.

I actually regret having quit there, but it wouldn't have mattered.
When I was there a Canadian company called Cinram had bought them.
Shortly after I quit, they shut down the plant and moved all the
operations back east.

Brian
--
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Seismic FAQ: http://www.skywise711.com/SeismicFAQ/SeismicFAQ.html
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