cr0sh:
charlieamer:
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:
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":
Free-space optical communication - Wikipedia
...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 
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