[Laser] Laser Digest, Vol 87, Issue 10

[Dave]

> Date: Thu, 22 Mar 2012 20:46:49 -0700 (PDT)
> From: MICHAEL COUTURE<mikecouture at bellsouth.net>
> Subject: Re: [Laser] Laser Digest, Vol 87, Issue 9
> To: wa4qal at ix.netcom.com,	Free Space LASER Communications
> 	<laser at mailman.qth.net>
> Message-ID:
> 	<1332474409.20757.YahooMailClassic at web180501.mail.gq1.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
>
> Dave,
>
> If it's the same one I have (laser project) Ramsey Electronics has them. Here's the link to the one I have:
> http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=LBC6K

That was actually Tim that said he's working on the low power laser 
transmitter; I merely
quoted his text that I was responding to.

I have used cheap laser pointers as communications links, but only for 
staged demonstrations, never "in the wild".  If you feed 4.5 Volts into 
one, and connect
that in series with a audio transformer so that you can vary the voltage 
slightly,
you can impose a very slight AM modulation onto the beam.  Don't push it too
hard, or you can blow the laser diode.  Most of those are supposed to 
have a
current regulator, but they will still let some modulation through.

Probably better, though, is to CW modulate the beam, with on/off keying,
using either Morse Code or some type of binary digital code.  I've done a
bit of that, too, using the output from the serial port of a PC to drive a
switching transistor connected in series with the power supply to a laser
pointer.

A variation on this is to logically AND in a 1 KHz tone to transmit 
modulated CW
(MCW), which makes the receiving end a bit simpler.  It no longer has to 
detect
the beam and key an oscillator with it; it only has to detect the beam, 
and run that
though an audio amplifier.

There are, of course, other variations.  One can pulse width modulate 
the beam
to transmit audio.  Or, one can digitally modulate the beam with a coded 
audio.

> I actually bought 2 of them for 2 way comms. Problem is nobody around here is into electronics.

Yeah, that's the same problem I have.  It seems that there's no one 
within line
of sight that is interested in pushing the upper frontier.  Oh, well, 
that's what I
get for living in a technological desert.  :-(

> Mike C.
> sandbar w/fl

Dave