[Laser] 5 mw laser transceiver kit

Mon Sep 20 15:37:08 EDT 2010

Hi James and all,

I too have a pair of the LBC6K transivers in an 'unfinished' state. Time to
heat up the soldering iron again. I have DVD, and some ebay laser diodes to
play with also. Time will tell. Good, now we're cookin'. Let's keep going.

As part of this discussion, how to measure power/lux/output of the laser of
choice should be included. I have a Tek J-16 and the necessary heads. I also
have some polarizing lenses. My thoughts were to calibrate the J-16 using
the polarizes to attn the sun to a usable level for the laser. (this assumes
a reasonable accurate input via known power being emitted by the sun on
earth). This is obviously a broad stroke but you get the picture.

Mike C.
(sandbar west FL)

-----Original Message-----
From: laser-bounces at mailman.qth.net [mailto:laser-bounces at mailman.qth.net]
On Behalf Of n5gui at cox.net
Sent: Monday, September 20, 2010 10:15 AM
To: Free Space LASER Communications
Cc: Tim Toast
Subject: Re: [Laser] 5 mw laser transceiver kit

An interesting suggestion Tim.

I started this reply comment to suggest that rather than trying to dismantle
a camera for lenses, one would have more predictable results and probably
far less work to order "educational" lenses from Surplus Shed.  They have a
series of various focal length double convex lenses in 50 and 38 mm
diameter.  The 50 mm lenses are currently available for $1.50 each or 10 for
$10. These are not commercial quality, but certainly good enough for what
you have suggested.  Available focal lengths are 50, 75, 150,  200, 250,
300, 500, 667, and 1000 mm.

The 50 mm lenses fit nicely inside 2" schedule 40 PVC plastic pipe, although
for a receiver system it might be better to consider the black equivalent.
To actually mount 50 mm lenses in 2" plastic pipe, I use a "test cap" as a
lens holder.  To hold the lens I cut a groove along the inside edge using a
drill press and rotary file.  An alternative that only requires simple hand
tools is a pair of rings cut from Sched 20 ( thin wall ) PVC.  The outer
ring can act as a spring to hold the lens in place, so that different lenses
can be exchanged.  For permanent mount, glue both rings.  

I should also point out that the Ramsey Electronics Laser Beam Communicator
kit is still available, although the price is now nearly $55.  For those not
familiar with the LBC6K, it has separate receiver and transmitter boards,
each of which will fit inside 2" plastic pipe.  I built a pair of them about
a decade ago, but the kit seems to not have changed, other than price.  I
was disappointed that the instructions did not suggest any way of mounting
the boards, other than to say they would fit in 2" plastic pipe.  The
transmit circuit uses a quad op amp and microprocessor to provide an
amplifier for the electret microphone, band pass audio filter 150 to 6,000
Hz, automatic level control, and pulse width modulator to a FET driver for
the "bullet style" pocket laser pointer.  The receiver uses a photo
transistor, similar audio amp and band pass filter feeding an IC audio amp
for earphones or small speaker.  It works.  It also has a lot of room for
experiementing and improvement
 - mechanically, electronically, and optically.  As for the price, compare
commercial kit suppliers of UHF or QRP amateur radio equipment to the group
buys of projects sponsored by various clubs.

The LBC6K has an advertised range of 1/4 mile.  The phototransistor it uses
has a 5 mm clear plastic housing, so estimate the performance using that as
the sensor size.  A 50 mm lens is 10X the diameter, therefore 100X the area.
If the laser pointer beam's spot expands to 10X the diameter, it will have
100X the area, hence 0.01 the brightness.  It is a fair assumption that
beyond 1/4 mile the beam expands linearly, so at 2.5 miles, the beam should
be expanded 10X diameter.  The beam will also weaken due to atmospheric
absorbtion in a linear fashion, but that may not be important for this
example.  This only shows what I mean by a lot of room for improvement.

I would like to see what sort of ideas come up.

James
 n5gui

---- Tim Toast <toasty256 at yahoo.com> wrote: 
> Hi All
> 
> It's great to see someone has put a kit together. That is sure to 
> spark some interest in optical coms. In the interest of a little fun 
> competition, it would be nice to have a simple kit for laser com's 
> too. One obvious advantage (or not so obvious) for laser over LED, is 
> size and power consumption. A simple laser transceiver could be made 
> very small and portable, even pocket-sized and battery powered. Under 
> 90 ma. for most 5 mw diodes.
> 
> It would help if everyone could start with the same size, easy to 
> obtain, enclosure. One that comes to mind is the old "Tuna Tin 2"
> kits. You could actually use a tuna can (Tuna Tin THZ or
> Tetrazzini?) but someone suggested to me to use one of those "Altoids" 
> candy tins. They have an easy access door and complete sheilding, plus 
> plenty of room for a circuit board and batteries inside. These are the 
> large 5" x 3" x 1" inch size boxes. They also come in a couple smaller 
> sizes and even round ones, all with resealable metal lids or doors.
> 
> I was looking at some amplifier circuits today and saw this high gain 
> hearing-aid design that uses 3 transistors and one battery (1.5v). If 
> you switch the microphone with a photo detector front end, you have a 
> high-gain receiver plus part of the transmitter too. A laser 
> transceiver could be made very small and energy efficient using a low 
> voltage like 3 volts (2 cells). A 3, 6 or
> 9 volt design for the small light-weight battery sizes. With a dual 
> 555 timer chip, you can have a simple high quality PWM AM for the 
> laser and a tone generator for MCW or alignment. The goals being low 
> cost, light wieght, easy to put together etc..
> 
> Relatively cheap optics that work well:
> If you are willing to take apart some junk equipment you can find lots 
> of optical goodies. The old VHS Camcorders can supply most of the 
> optical parts. An old DVD player will get you a 5 milliwat red laser 
> diode (these are often dual wavelength visible/IR diodes with three 
> pins, or four pins if it has a monitor diode) and some small lenses to 
> use. These even have one lens you can use to collimate the laser 
> fairly well (the laser pickup "output" lens is a 5mm or 6mm f0.9 or 
> faster type) or it can adapt the beam for use with a larger lens. The 
> main large glass lens on the camcorder is usually a 25 to 50mm f1.0 
> type when used by itself. It can work for either transmitter or 
> receiver. Some of the older ones have a fine adjustment twist focus.
> For short range use, it might be nice to be able to defocus the 
> transmitter and receiver some - up to 10 degrees or more maybe - these 
> twist focusing lenses would be great for that.
> Inside the camera zoom lens are a few smaller glass lenses in both 
> positive and negative types plus a special "eyepeice" type assembly
> - similar to a 15 - 20mm Kellner telescope eyepiece. This could make a 
> nice finder when paired with a larger objective lens and a cross-hair. 
> The video viewfinder eyepiece is also adjustable and could be used for 
> either one or a finder. It is usually a 20mm F1 or F2 plano convex 
> plastic lens.
> The performance won't be excellent obviously with these small lenses 
> but should work for the shorter ranges ok. (under 50 miles or so?? :) 
> you can always break out the big optics for better performance.
> 
> 
> tim toast

______________________________________________________________
Laser mailing list
Home: http://mailman.qth.net/mailman/listinfo/laser
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Laser at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html