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Hello, this is one of my first posts here, so i didn't know where exactly to put this tupic so I put it in general discussion. I've encountered this project: http://www.instructables.com/id/Laser-Transceiver/ . It is basicly a serial data communication using laser. There are lasers that are visible over a great distances, so I wanted to set this up so that I can communicate with my friend that lives about 2km away from me. I have three questions:
1. ) Are there any legal issues on using lasers for such great distances ? (at least in your country)
2.) What laser color do you recommend ? I was thinking about IR, but during the setup, if we accidently don't aim laser exactly at receiver end, we could potentionally burn something with such powerful lasers.
3.) (Most important) How do we aim lasers at such distances ? Maybe if I have coordinates from google earth and take some super precise compass, or something ... dunno ... any ideas ?

Any help is apprecieted. Thanks in advance.
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Hello, this is one of my first posts here, so i didn't know where exactly to put this tupic so I put it in general discussion. I've encountered this project: http://www.instructables.com/id/Laser-Transceiver/ . It is basicly a serial data communication using laser. There are lasers that are visible over a great distances, so I wanted to set this up so that I can communicate with my friend that lives about 2km away from me. I have three questions:

Your might want to investigate this long-running project:

http://ronja.twibright.com/

It doesn't use lasers, but rather extremely bright near-IR LED arrays for the transmission end, and a focused telescopic system on the receiver end to collect the light for the photosensor(s). The project's main complexity, though, comes from the hardware on either end to convert from ethernet and back (yep - real networking, not just simple serial comms).

BTW - what you are trying to build is termed "free-space optical communications":

http://en.wikipedia.org/wiki/Free-space_optical_communication

...and actually has a fairly long history behind it (see the above link). Such communications systems are used all over the world and have been extensively developed (and deployed commercially). You would do good to research the topic as much as possible before building anything.

You might also be interested in looking into Forrest M. Mims III's Engineer's Mini-Notebooks:

http://www.forrestmims.com/engineers_mini_notebook.html

One of them, "Communications Projects" (volume 2 in the new series) - has a lot of good information on building such circuits (though for audio transmission - but you could do audio modem comms that way); again, nothing on lasers - just LEDs and IR photo-transistors and the like.

You might also want to pick up all the books in that series - they are a great resource to have on the shelf!

1. ) Are there any legal issues on using lasers for such great distances ? (at least in your country)

I don't know what the legalities are here in the USA; I would think that most companies deploying a commercial system would build so-called "eye-safe" devices (likely using a red laser, 5 milliwatts or under); for the human eye, IR doesn't trigger a blink response until long after the damage is done (which is why you should be very, very careful around IR lasers and high-lumen IR LEDs; wear proper filtering goggles - also, be very careful around green lasers; the cheap ones from china generally use a higher-power IR laser to pump a crystal that shifts the frequency to green - but still pumps out a ton of IR!).

That said, you'll probably want to review everything you can on any legalities; as far as I know, there are no FCC limitations, but there might be "public-use" limitations for the county/city/state/town you are in (or whatever it is for your country) - basically stuff to prevent bystanders from being blinded, limitations to address issues of pilots being blinded, etc.

I would say, though, if you stayed away from lasers, and used high-lumen red or near-IR LEDs, and proper optics systems, and didn't aim them toward close-by windows or such, and kept them elevated out of the line-of-sight of any pedestrians or such - you'll probably be ok. Otherwise, do your research, and spend the money to consult with a lawyer, if you have to.

2.) What laser color do you recommend ? I was thinking about IR, but during the setup, if we accidently don't aim laser exactly at receiver end, we could potentionally burn something with such powerful lasers.

What you'll likely burn is your retina (due to the lack of your eye having blink response to IR, as noted earlier). All lasers diverge (spread out) in the end - in fact, if you insist on using a laser, you'll want to find what its divergence is over distance. Cheap handheld lasers will diverge greatly even over 10 meters (you start out with a dot just a few feet away; 10 meters away, that dot has grown to a spot 5 cm in diameter). The nice thing about that divergence is that it makes it more "eye-safe"; the bad thing is that as the distance grows, so does the divergence, and so does the size of your "collector" optics.

Again, I would recommend against using lasers (or at the very least, using tight collimation for the output), and particularly IR. IR, of course, is best for this kind of work, but it can be dangerous to work with; as long as you understand the dangers involved, and take precautions, then it can be safely worked with.

3.) (Most important) How do we aim lasers at such distances ? Maybe if I have coordinates from google earth and take some super precise compass, or something ... dunno ... any ideas ?

First off, realize that to communicate over 2 km will mean that you are going to be elevated somewhat, so keep that in mind (take the usual precautions as needed).

For aiming, the easiest and cheapest way would be to use a visible light source at each end, and eyeball focus "down the barrel" of the receiver optics; this of course is very dangerous, especially if using IR (well, it would be impossible using IR) - even using red lasers, it would be dangerous.

Better might be to set up the system, get it aimed "roughly" by sighting each other (without any lasers or other light turned on) using telescopes and/or binoculars, then continue to sight-in using the optics of the system (without sensors or output turned on and in the way).

Once you have it roughly sighted, then to dial it in better will mean have some means to monitor to output of the receiver, and some means to carefully change the position of the transmitter and receiver alignment. First, you will want to mount both securely so they don't move, then do the rough sighting. Then, set up the system so that you can transmit a simple carrier wave or something from one direction to the other. You could then listen to the carrier wave (if in audible frequencies), then adjust stuff on either end until the signal is as loud as possible. Or you can use an o-scope to monitor the signal until the amplitude and waveform look as clean as possible. One person on each end will be needed; you'll probably want radios as well to stay in communication with each other, and to relay information about the quality, etc. Your adjustment system will need to have some means to make fine adjustments to the angles - keep that in mind (such outdoor tripods aren't cheap; then again, I don't know your budget - you might be able to get away with cheaper photography tripods if this isn't meant as a permanent long-term setup).

Something else to keep in mind - unless you mount the system very well, or have some means to deal with noise and such, your signal will likely drift in the wind and such, as the tripods and other equipment moves. Commercial systems have auto-aiming servo-mechanisms (which almost eliminates the need to "dial in" the position manually), that can correct for the drift and keep the signal at a high-quality level. Something to keep in mind, anything (climbing a pole or futzing with things on a roof constantly can get old quickly).

Good luck, hope this helps...
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The big problem not focussed upon (sic.) in the description above, is the practicality of "line of sight" and reliability.

You have a friend living 2km away.  Can you see his home from yours?  If you cannot, then you clearly cannot communicate with optical communications.  If you can - presumably you live in high-rise - how often can you not due to fog, smoke, smog etc.?

What you should be researching instead, is W-Fi (802.11) using directional (dish) antennae.  You might get away with a planar array antenna.  The equipment is readily available with little or no modification and much less affected by fog and such (but can be affected, as with your TV reception and optical communication, by temperature inversion).

You need to consider minimising any length of RF cabling as cable losses at 2.4GHz are substantial, mount your Access Points behind the dish in weatherproofing, but all things considered, this will be more practical than optical, aiming much less critical and "line of sight" whilst still relevant, much more tolerant.

So why is radio so much more effective?  A lower "noise floor" for one, less atmospheric absorption and more effective signal amplification.
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Hello, this is one of my first posts here, so i didn't know where exactly to put this tupic so I put it in general discussion. I've encountered this project: http://www.instructables.com/id/Laser-Transceiver/ . It is basicly a serial data communication using laser. There are lasers that are visible over a great distances, so I wanted to set this up so that I can communicate with my friend that lives about 2km away from me. I have three questions:

Your might want to investigate this long-running project:

http://ronja.twibright.com/

It doesn't use lasers, but rather extremely bright near-IR LED arrays for the transmission end, and a focused telescopic system on the receiver end to collect the light for the photosensor(s). The project's main complexity, though, comes from the hardware on either end to convert from ethernet and back (yep - real networking, not just simple serial comms).

BTW - what you are trying to build is termed "free-space optical communications":

http://en.wikipedia.org/wiki/Free-space_optical_communication

...and actually has a fairly long history behind it (see the above link). Such communications systems are used all over the world and have been extensively developed (and deployed commercially). You would do good to research the topic as much as possible before building anything.

You might also be interested in looking into Forrest M. Mims III's Engineer's Mini-Notebooks:

http://www.forrestmims.com/engineers_mini_notebook.html

One of them, "Communications Projects" (volume 2 in the new series) - has a lot of good information on building such circuits (though for audio transmission - but you could do audio modem comms that way); again, nothing on lasers - just LEDs and IR photo-transistors and the like.

You might also want to pick up all the books in that series - they are a great resource to have on the shelf!

...

Good luck, hope this helps...
Thank you for your time. This just a hobby project, so I would do it just for fun. I wanted a data transmission and audio transmission, I'd make my own protocol, wouldn't be a big problem, just simple stuff. I saw ronja project, and I like the principle, although I didn't find an explanation of how optics work, guess that's physics primer. If I understood correctly, by using this kind of lens, if put on exact spot, I could make led light (ex. the one that gives light at 30° view angle) go parallel, so I get bigger radius of light going parallel, then the one with traditional lasers ?

EDIT: Turns out you have to put lens on distance, that is exactly the same as it's focal length, from the LED in order to make parallel light. I think it is much more easier if you aim it with a 'laser' whose radius is 20cm then the one that is 1cm smiley still, it is hard to put lens to that precise distance from LED, but still could be better then shooting in blind with laser pointer
« Last Edit: November 02, 2013, 06:44:48 pm by charlieamer » Logged

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You have a friend living 2km away.  Can you see his home from yours?  If you cannot, then you clearly cannot communicate with optical communications.  If you can - presumably you live in high-rise - how often can you not due to fog, smoke, smog etc.?
I can see his home from mine. We are both living on two different hills facing each other. Fog is a problem only in early hours of morning, during day it is very clear.
What you should be researching instead, is W-Fi (802.11) using directional (dish) antennae.  You might get away with a planar array antenna.  The equipment is readily available with little or no modification and much less affected by fog and such (but can be affected, as with your TV reception and optical communication, by temperature inversion).
Well I was more looking for a simpler communication like audio transmission, so FM could be usable, or simple RS232. How small dispersion in antennae can be ? Don't want any legal issues here smiley-razz (I am not ham radio operator or something, i.e. I don't have license to transmit data over radio on great distances.)
So why is radio so much more effective?  A lower "noise floor" for one, less atmospheric absorption and more effective signal amplification.
True, true ... But laser data transmission has bigger data transfer rate, so I could connect two computers on LAN later at some point without much expenses (WiFi would be more expensive, but still, I'll try that one out later smiley )
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I think it is much more easier if you aim it with a 'laser' whose radius is 20cm then the one that is 1cm smiley still, it is hard to put lens to that precise distance from LED, but still could be better then shooting in blind with laser pointer.

Not sure what you are getting at here, but it is the case that you need a lens with the laser as well; the minuscule lenses with short focal length on laser pointer/ entertainment models have quite a wide dispersion; you really still need to use a telescope of some sort.

Well I was more looking for a simpler communication like audio transmission, so FM could be usable, or simple RS232. How small dispersion in antennae can be ? Don't want any legal issues here smiley-razz (I am not ham radio operator or something, i.e. I don't have license to transmit data over radio on great distances.)

Broadly speaking, no-one is going to notice a "Wi-Fi" link since there are so many of them and it is in an ISM band; you are using pre-built and certified equipment and 1 metre dishes are all over the place.  Strictly speaking, you would be exceeding the ERP specifications but again, outside of the beam itself, the power will be less than usual anyway.

True, true ... But laser data transmission has bigger data transfer rate, so I could connect two computers on LAN later at some point without much expenses (WiFi would be more expensive, but still, I'll try that one out later smiley )

Given the availability of the equipment, Wi-Fi is dirt cheap; cheaper than optical!

And laser data transmission has a much poorer data rate unless you use quite sophisticated equipment - modulating a common laser above the audio range is non-trivial but more particularly, achieving greater bandwidth with any usable sensitivity using photo-diodes requires more sophistication due to junction capacitance.  Amplitude modulation of lasers is poor, so you would indeed be wanting to use FM.
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Quote from: charlieamer on November 02, 2013, 09:44:34 pm
I think it is much more easier if you aim it with a 'laser' whose radius is 20cm then the one that is 1cm smiley still, it is hard to put lens to that precise distance from LED, but still could be better then shooting in blind with laser pointer.
Not sure what you are getting at here, but it is the case that you need a lens with the laser as well; the minuscule lenses with short focal length on laser pointer/ entertainment models have quite a wide dispersion; you really still need to use a telescope of some sort.

This is what I was talking about. This principle will make the light go parallel.
Quote
Given the availability of the equipment, Wi-Fi is dirt cheap; cheaper than optical!

And laser data transmission has a much poorer data rate unless you use quite sophisticated equipment - modulating a common laser above the audio range is non-trivial but more particularly, achieving greater bandwidth with any usable sensitivity using photo-diodes requires more sophistication due to junction capacitance.  Amplitude modulation of lasers is poor, so you would indeed be wanting to use FM.
Yeah ... guess u r right ... I'll open new thread about this when I finish this communication with laser, and then I'll compare results of the two smiley Thank you very much for your help.
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