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?

[autopr0n]

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

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...

[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.

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.

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.

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?

[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.)

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.

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]

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: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.

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: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.