Build Your Own 10Mbit/sec Optical Data Link

redcliffe writes: "This website has complete plans to build a 10 megabit per second optical data link that can work over up to 1 kilometre. It uses fairly cheap components, such as standard LED's instead of laser diodes. This also makes it a lot safer to work with, i.e. you won't burn your eyes out if you accidently look into it."

Comments

Why not 802.11b?

[msolnik]

The equiptment is cheaper easier to make/get and can get further range. I can get upto 15 miles in Houston with 2 15db direction antennas that you can get for 40$ a peice.

Re:Why not 802.11b?

[laserjet]

You have a good point, and 802.11b probably would make sense in most conditions. The only benefits that this would offer you are 1) if you work in an area that has too much RF interference for 802.11b to work correctly, and 2) this would be more secure that 802.11b. For instance if you want to run a connection to your neighbor across the street, to intercept your connection, someone would have to get exactly in line with the transceiver, whereas 802.11b is broadcast all over the place.

Aside from that, it just looks like they built it because they could, and that, is reason enough.

Re:Why not 802.11b?

[abnormal]

Why not use any existing technology? The reason is that it's a cool project to do between you and your geek friends. Anyone could go out and buy necessary hardware to do anything.. but to say you built it, it's pride you can't buy. =)

Re:Why not 802.11b?

[autopr0n]

He's talking about directed 802.11, not Omnidirectional. omnidirectional WiFi dosn't get nearly that range

Re:Why not 802.11b?

[redcliffe]

Yeah, for long distance 802.11 is going to be the way to go, although I am going to experiment with methods of getting more range out of it. If you only have a short distance, like to go a couple of streets away, this may be cheaper.

Re:Why not 802.11b?

[dattaway]

since when does IR not need direct line of sight?

The lack of blinky light innovation of the average person amazes me. Improvise:

Bounce it off the building down the street. Perhaps up the power and bounce it off the clouds like weather radar. Integrate your LED Christmas lights as the emmiters. Hook up the ethernet AUI connection to the flyback circuit on your television for Van Eck transmission. Complete the optical link by using the FBI's monitors in the van down the street as the optical receiver. The possibilities of bending light around the corner are endless!

Re:Why not 802.11b?

[laserjet]

I stand corrected. Good point, sir.

bah

[nomadic]

This also makes it a lot safer to work with, i.e. you won't burn your eyes out if you accidently look into it.

Well where's the fun in that?

How do you aim with these things?

[Anonymous Coward]

you wont be able to see em from 1km away, so how would you kow where to aim the things?

A Christmas Story

[Anonymous Coward]

You'll shoot your eyes out! You'll shoot your eyes out!

Re:Immune to interferience?

[jpmkm]

Are you implying that pigeons shit sideways?

Doh! Watch where you point that thing...

[kordless]

"This also makes it a lot safer to work with, i.e. you won't burn your eyes out if you accidently look into it."

It looks as if the author has learned this first hand if the font size on the instructions is any indication.

Check out Grub!

Sigh...

[cperciva]

It uses fairly cheap components, such as standard LED's instead of laser diodes. This also makes it a lot safer to work with, i.e. you won't burn your eyes out if you accidently look into it.

The mere fact lasers are used in most fiber optics does not immediately render them dangerous. Typical power levels are on the order of a few mW, far too low to cause any permanent damage.

Re:Sigh...

[mlknowle]

Exactly - the biggest saftey risk here is those nasty cuts you can give yourself with Fiber Optic tubing.

I once had a .5mm strand of the stuff stuck in my thum - it took weeks of soaking in warm water to get it out.

Re:Sigh...

[dattaway]

I wish this were true. Many years ago, I was fascinated by lasers; unfortunately, infrared isn't too visible. Several years later, I now have dark stuff floating around in my eyes. For a person 33 years of age, I would not recommend looking at concentrated sources of energy, no matter how small.

It may be a milliwatt, but its still heat: focused smaller than the head of a pin. It may burn. Damage in the eyes shows up many years later.

Re:Sigh...

[zenyu]

Floaters are normal. Well if your retina could be flacking off but seeing floaters isn't so surprising in a 33 yo. or 25 yo. for that matter.

But even those LED's they are using will hurt your eyes if you stare at them for a few minutes. IR is nasty, it dries your contacts while looking like a not so bright red LED...

This is why I read Slashdot

[Kaypro]

This is absolutely great! A primo example that goes back to the roots of Slashdot.

Excellent link, great article.

Now where's my soldering gun?

:-)

Re:This is why I read Slashdot

[JesseL]

Jeez, if you use a soldering gun to put this together you'll end up with modern art long before you'll get a working data link. I wouldn't try it with anything more than a 30W iron.

Re:This is why I read Slashdot

[cymen]

I agree and friends justify for friends the benefits of buying Weller soldiering tools too :).

Re:laser diode

[Drakula]

The laser diodes in laser pointers cannot be used for a number of reasons, here are a couple: 1) Wrong wavelength: you need lasers with a wavelength near either 1.3 microns or 1.55 microns to take advantage of the disperison and attentuation minimums of optical fiber. Laser pointers have wavelengths in the visible, near 650nm. 2) Very narrow linewidth is need to reduce pulse spreading . Laser pointer devices are relatively broad.

There are others but I can't think of them right now.

Just fyi...

My favorite warning sticker

[shoppa]

i.e. you won't burn your eyes out if you accidently look into it.

Reminds me of my favorite warning sticker:

Warning: Do not look directly into laser with remaining good eye

Despite how effective the sticker was at reminding us to keep our goggles on, the safety people made us take it down.

Laser?

[mindstrm]

The article quite clearly states that for 10M, they use a laser diode...

Hmm

[Chazmati]

From the "Making the electronics" section (emphasis mine, of course):

Solder remaining parts into the transmitter. Put the three 74HC04's in stack (like they are fucking), and solder pins of equal numbers together. The schematic follows.

Nice.

Got AUI?

[Uller-RM]

Has anyone else bothered to read this enough to notice that it will not work with twisted pair Ethernet? It requires an AUI connection. They even say in the FAQ, redesigning it to work with TP would be a pain in the arse.

In order to use the circuit, you have to either buy an AUI->TP transciever, or set up a bridging machine.

Just saving a bit of time for some people who are no doubt running out to Ripoff Shack grabbing l33t bl00 leds.

Re:Got AUI?

[neonstz]

Well, getting used NICs with AUI should be a problem I think. I've bought quite a few at large garage sales. If it is a problem getting one however, just get a Sun Sparcstation 5 or some other machine with built-in AUI. :)

Re:Got AUI?

[Uller-RM]

Ethernet over TP implements a link integrity signal. AUI does not. That's the main barrier to using this particular rig - you'd have to come up with an emulator for that signal, or the cards would refuse to transmit.

(And FYI, you're partly right. Ethernet over TP uses Manchester encoding, which means that it watches for changes in logic rather than states - i.e. transitioning from ground to 5V is a 0, and 5V to ground is a 1. Hard drives actually also use this method.)

Re:Got AUI?

[Zog]

It's not the end of the world. AUI adapters are easy to find and are pretty cheap (mine was ~$10 from a store that sells random computer cables/adaptors; they can be had online for about the same).

Also, using AUI makes a fair amount of sense - it *is* simpler, so you don't have to worry about the signals as much, so it's easier to make at home :)

Now, compare the price of parts plus the AUI adapter (I'll let you do that one) to the price of a cheap (though crazy fast) commercial link, and it should make sense why this is good. Also, as someone else already stated, there's the simple fact that you're using your very own homemade optical datalink ;)

Re:Got AUI?

[Restil]

Huh? A LOT of older ethernet network cards have AUI connectors. You don't see them on the 100mbps cards but since this maxes out at 10mbps anyways, who cares? If you're going to spend the time building this device, getting ahold of a compatible network card is not the biggest obstacle. :)

-Restil

Play with my webcams and turn my lights on/off at http://206.54.177.105

Uses the AUI interface

[Animats]

This works because the AUI interface is still around. That's the original, really simple, interface used with the original Xerox PARC Ethernet tranceivers in the 1970s. It still works.

Others have done similar things with the AUI interface. Here's an RF link using the same technology.

If you want more range from the optical link, I'd suggest putting an optical interference filter (from Edmund Scientific) in front of the receiver. Pick one that matches the color of the transmitted beam, and you'll reject most other light.

Huh?

[autopr0n]

You can't actualy go blind from looking at the sun. I have no idea where that idea came from. I looked into the sun all the time as a kid. It hurt a little and can degrade your vision if you do it a lot, but it isn't going to be the last thing you ever see. Evolution isn't that stupid.

Use these for backbone of (community) wireless?

[Brian Stretch]

These, or higher-speed commercial point-to-point transmitters, seem like a neat way to set up a wireless backbone for a (community) wireless network. Then you just hang WiFi transmitters off the backbone access points. Actually, I'd want something a bit faster than 10Mbps for a backbone (aggregate multiple transmitters?), but you get the idea. I'm not sure it'd be superior to using the new 802.11a 5GHz gear for such a backbone, but in either case, you avoid dealing with the local telco monopoly, which is always a Good Thing.

Maybe put small caching proxy servers at the access points backed up by a big one at the end of the network? Or just the latter. If you're liable to wind up with a Linux box at the access points anyhow...

I've already got a cable modem and I'm lazy, so I'll let someone else run with this :-).

Fiberless Optical Networks

[Alien54]

There was this old story about a company doing something similar with lasers between skyscapers, etc. I suppose the usual fog and bird problems apply. And maybe some mean spirited neighborhood kids with a couple of balloons

Personally, I wouldn't mind a way to do this sort of thing by shortwave. It would be great for WAN applications between cities [shrug]

Re:Fiberless Optical Networks

[ameoba]

My school uses a 10Mb line-of-sight microwave system that covers about 3-4 blocks, between the main building and an annex; living int the rainy Pacific Nortwest, if rain caused it problems we would know.

IIRC, Ma Bell used to use microwave connections for long-distance lines

Laser warning:

[swordboy]

****Caution - do not look into laser with remaining eye!****

Eye burn?

[rew]

This also makes it a lot safer to work with, i.e. you won't burn your eyes out if you accidently look into it."

Ehmm. Modern High efficiency LEDs also carry the "don't look directly into this" warnings. And those things are BRIGHT.

Roger.

Re:Not to mention reliability...

[markov_chain]

What are you talking about? The guy built 10 Mbps transceiver out of some LEDs-- a far cry from 10 Gbps. He used ordinary Ethernet NICs with AUI ports and converted the signal into light. Replacing the LEDs with laser diodes should be easy .

Re:Immune to interferience?

[weakpunk]

African or European pigeons?

Re:Shortwave

[billstewart]

Close, but nobody smokes cigars any more.
The most popular stuff seems to be 1200 baud on 2-meter, which is line-of-sight plus repeaters, though there's some 300 baud HF stuff that has more chance of going city-to-city, and some fancier 9600 baud stuff.

Here's some text snagged from The FAQ at TAPR.ORG

TNC (terminal Node Controller)
A TNC contains a modem, a computer processor (CPU), and the associated circuitry required to convert communications between your computer (RS-232) and the packet radio protocol in use. A TNC assembles a packet from data received from the computer, computes an error check (CRC) for the packet, modulates it into audio frequencies, and puts out appropriate signals to transmit the packet over the connected radio. It also reverses the process, translating the audio that the connected radio receives into a byte stream that is then sent to the computer.

Most amateurs currently use 1200 bps (bits per second) for local VHF and UHF packet, and 300 bps for longer distance, lower bandwidth HF communication. Higher speeds are available for use in the VHF, UHF, and especially microwave region, but they often require special (not plug-and-play) hardware and drivers.

Computer or Terminal
This is the user interface. A computer running a terminal emulator program, a packet-specific program, or just a dumb terminal can be used. For computers, almost any phone modem communications program (i.e. Procomm+, Bitcom, X-Talk) can be adapted for packet use, but there are also customized packet radio programs available. A dumb terminal, while possibly the cheapest option, does have several limitations. Most dumb terminals do not allow you to scroll backwards, store information, upload, or download files.

A radio

For 1200/2400 bps UHF/VHF packet, commonly available narrow band FM voice radios are used. For HF packet, 300 BPS data is used over single side band (SSB) modulation. For high speed packet (starting at 9600 bps), special radios or modified FM radios must be used. 1200 bps AFSK TNCs used on 2-meters (144-148Mhz) is the most commonly found packet radio.

There's just one problem with these. :)

[edunbar93]

I live in Vancouver, and wintertime reduces the range of these devices to much less than 1 KM. Much of the time when it's raining, visibility isn't that great, and these things require telescopic lenses to get even 1KM range.

I would have to wonder whether this would be much more effective indoors however. It's much more secure (to block packet sniffers, simply close the curtains) than wireless would be, if only you could make the device small enough to put a little blinkenlight in your ceiling that would relay packets around. (in the ceiling because you don't want your cat getting in the way of your data transfers...) It might be a neat project. :)

Also Terabeam

[billstewart]

In addition to AirFiber, there's also Terabeam doing building-to-building optical technology. They're in the 100Mbps - 1Gbps speed ranges, with distances of 1km if you don't have fog, or 500 meters if you get fog (they're based in Seattle, so they've had plenty of weather to get real experience with :-) I think there are also a variety of other equipment makers.

Re:Hmm

[penguin_nipple]

Then you should be hawking your second hand hardware on eBay rather than hanging out on Slashdot. Years ago, stories like this were far more common on Slashdot, this is "News for Nerds, Stuff that Matters".

It's not about marketing it, selling it, etc. It's about doing it yourself.

OT a little but stuff optical, go with speakers :)

[new500]

. .

Hey, flame / mod me away here - I deserve it because I've been looking for a thread in which to post this rejected story sub from a week ago . . But what the heck here it is anyway :

( I was originally going to say this post is well OT because of the distance limitations of the below, but what about using this transmission in a PA system at a stadium, or a train station, where volumes and hence transmission possibilities are greater / farther? And just how much is over the air networking really explored by companies? This story is already dang good and right where it hurts for community and campus networks, but if I were building this kit for business I'd be thinking that planning permission would be the area I'd be researching most. In other words, do the "amateurs" have a real chance at a lead in this technology, especially price / performance wise? After all, you and I personally *don't* have to make budgets for contingent liability just in case the town planning dept. gets difficult. I'm all for guerilla networks - take a look at the below . . )

Aerial Acoustic Communications

Network with just a pair of pc speakers and a $5 mic! This recent paper explains the theory and writes up the experiment.

This may not be the answer to all your needs - 1000bps was one of the best results - but the authors talk about short distance communications for PDAs, or a television using sound for remote control. The environmental noise against which the authors deployed Spread Spectrum techniques, and a reference to audio steganography make for interesting reading, and radio hams may appreciate the use of FSK. Is this the future, or just a hint that playing albums backwards wasn't really the way to get the message?

There's also a lecture video here which was held at PARC on 11/8/01. You can grab the stream as a file using ASF Recorder or you can read up on some applications musings here. Happy Listening . .

.

Re:Expensive?

[cymen]

Well you can get the 64/40 bit WEP 802.11b Orinoco cards for $60 from places like JustDeals.com - wait, I see some Proxim ones for $40... I haven't dealt with JustDeals.com (got Dell OEMed Orinoco stuff before I found out about JustDeals) but the price sure sounds good.

I agree on loosing the omnidirectional stuff but another card would solve that problem ;).

Re:OT a little but stuff optical, go with speakers

[Lumpy]

DING...

I have a Tv from 1978 that uses acoustics for the remote control... very very old technology, doesnt work very well. was abandoned by most sane companies by 1980. Xerox is far from sane anymore.

One kilometre.

[exceed]

... 10 megabit per second optical data link that can work over up to 1 kilometre.

Does this data link retain it's speed of 10mb/sec even when you get further out towards a kilometer? I'm sure that you probably lose some packets along the way, kind of like CAT5.

Re:One kilometre.

[redcliffe]

AFAIK, it either works or it doesn't. Like you get 10mb/sec or you get nothing. There is no link quality control on it from what I can see.

Re:What's I find funny...

[redcliffe]

Never saw that one. You should have submitted it as a story.....

Re:Eye Safety story time

[cperciva]

From Health Canada:
But at levels between 1 and 5 mW, so much light rushes into the eye that it suffers a temporary condition called flashblindness. It is similar to the effect that occurs during flash photography where the image of the flash source remains in the eyes for a few seconds and then fades away. There is no long-term effect from flashblindness.

It may not be particularly pleasant to have one of these lasers hit you in the eye, but it won't do any permanent damage.

Define "safe"

[tzanger]

This also makes it a lot safer to work with, i.e. you won't burn your eyes out if you accidently look into it."

The site says the EIRP is 10kW -- you will most certainly be hurt if you stare into this thing!

Re:It makes sense as written

[david duncan scott]

and fliping the length specification to postfix for clarity

So the need to rewrite the comment for clarity helps demonstrate the clarity of the original?

Face it, it was an awkward construct. This ranks about one millionth on my list of important things, right after Gilligan's Island, but it produced this cascade of comments in classic Slashdot fashion (and even resulted in my being called an "assfuck" by some illiterate who apparently can't follow a thread or doesn't understand that some comments may be hidden from him)

Personally I'm happy to live in a world in which so many of us have so little to do. :)

Re:What's I find funny...

[cr0sh]

Probably should have - I probably didn't because many of the stories I have submitted in the past (with the exception of a few "Ask Slashdots") have been turned down (only to "of course" appear later).

Anyhow, it may have not stood out in my post because I got lazy and didn't set the links up properly - just bleched them on the page...