LEDs as data links

Experts envision using LEDs as data links over short distances. According to the article, white LEDs can send data at 80 Mb/sec while red and green ones can transmit at 200 and 500 MB/sec, respectively.

Soon our flashlights will be able to do double duty. Outfitted with flash memory and a receiver, you would be able to send, receive, and transport data.

Complete article here.

Neat. I think one of our members already mentioned doing something like that!

LEDs in data aren't all that new, though. I believe 850nm LEDs are used in networking, for 100BaseFX and 1000BaseSX (Fast/Gigabit Ethernet) over multimode fiber. The article is still interesting because it refers to free space optics (no wires/conduits), whose role has been typically filled by lasers.

Cool article... is this similar to fiber optics?

-Mike

FSO is essentially fiber optics without the fiber. It uses similar electronics but replaces the fiber fitting with a lens and some auto-position-correction servos to account for building sway.

I've build a couple of experimental FSO links (video & Ethernet) using the Sharp LT022 series of IR lasers. There are several commercial manufacturers of this stuff including Canon's CanoBeam series.

There are several challenges with the systems being described in that article, including those of stray ambient light raising the noise floor, as well as 20khz+ harmonics that are thrown out by electronically-ballasted fluorescents. Plus all of those light-bulb transceivers would have to be wired back to a central switch, and each light bulb might have to have it's own IP address. Gosh, a lightbulb that issues a DHCP request when it's screwed in!
/ubbthreads/images/graemlins/crackup.gif

[ QUOTE ]
PhotonWrangler said:
Plus all of those light-bulb transceivers would have to be wired back to a central switch, and each light bulb might have to have it's own IP address. Gosh, a lightbulb that issues a DHCP request when it's screwed in!
/ubbthreads/images/graemlins/crackup.gif

[/ QUOTE ]

/ubbthreads/images/graemlins/str.gif /ubbthreads/images/graemlins/aaa.gif NOOOOO!!!! They're coming for us!! *rushes off to grab carbine with SF 1913 rail and M900A Universal System* The computers are taking over the world!! /ubbthreads/images/graemlins/crackup.gif

It sounds like the perfect application for Power over Ethernet to me though.. since you can pump up to ~15W of 48VDC power to each outlet today, that's a lot of LEDs you can drive. You will definitely need a step-down and signalling electronics to get the power (it won't supply power till it receives your signal), but that could be 3 Luxeon Vs driven at spec or slightly underdriven for longer life.

Uh, I think it's been done. Look at the IrDA port in every notebook and PDA. That's simply and infrared LED driven at a specific freq.

The Timex data watch used light (from your screen) to download data to the watch.

One of the "spy" books had a nice little writeup on tapping a phone by reading the changes to the LED that lights up when you take the phon off the hook. Many hardwired phones simply lit the LED from the same line that carries you voice, so the light was modulated by the voice signal. It could be read from outside a window or across a noisy office.

With 2.4 ghz (unlicensed) and other microwave (licensed) available for point to point between adjacent buildings, the use of visible light just seems to be too much problem. Rain and dust would create major headaches. Fog would add to the frustration in places along the coast.

802.11G between buildings? It's been done. Cheap, easy and no license required. Unfortunately, there's little light involved with 802.11. /ubbthreads/images/graemlins/smile.gif

Daniel

[ QUOTE ]
KevinL said:
[ QUOTE ]
PhotonWrangler said:
Plus all of those light-bulb transceivers would have to be wired back to a central switch, and each light bulb might have to have it's own IP address. Gosh, a lightbulb that issues a DHCP request when it's screwed in!
/ubbthreads/images/graemlins/crackup.gif

[/ QUOTE ]

/ubbthreads/images/graemlins/str.gif /ubbthreads/images/graemlins/aaa.gif NOOOOO!!!! They're coming for us!! *rushes off to grab carbine with SF 1913 rail and M900A Universal System* The computers are taking over the world!! /ubbthreads/images/graemlins/crackup.gif

It sounds like the perfect application for Power over Ethernet to me though.. since you can pump up to ~15W of 48VDC power to each outlet today, that's a lot of LEDs you can drive. You will definitely need a step-down and signalling electronics to get the power (it won't supply power till it receives your signal), but that could be 3 Luxeon Vs driven at spec or slightly underdriven for longer life.

[/ QUOTE ]

Actually this is the reverse - Ethernet-over-Power. /ubbthreads/images/graemlins/tongue.gif
I suppose you could modulate the 60hz (or 50hz) with a low-level data carrier and then couple it to the modulation driver stage of the LEDs through a high-pass filter. I know that HPNA does this already, sorta, only the end device doesn't emit photons.
/ubbthreads/images/graemlins/icon3.gif

Good points, Daniel.

The one advantage that light has over 802.11x is that light can easily be segregated from room to room, so that a smart home could tell which room you were in at the moment and route inbound traffic accordingly. Assuming that you would want it to do that, of course! There are certain rooms in the house where I don't wanna be tracked, dontcha know.
/ubbthreads/images/graemlins/smoker5.gif /ubbthreads/images/graemlins/blush.gif

Last year I piicked up an interesting little gizmo from a local discount store. It was a children's "PDA" toy, a functioning replica of a stripped-down personal organizer. The user can store phone numbers and a few other odds and ends in it, but it doesn't have a keyboard for the entry; instead, you run a little app on your PC that turns the data into flickers of light on your CRT, then you hold the backside of this device (where the photocell is) up to the CRT to transfer data into it! Clever idea, although it only has a ranger of an inch or so. But it could be a predecessor of similar approaches in the future.

We have an ongoing effort at work to look at high power UV LED's as free-space transcievers. They're looking to put these on netted battlefield sensors so they can communicate with one another at ranges of a few hundred meters. Idea is to use the natural backscatter properties of the atmosphere to make them omnidirectional.

[ QUOTE ]
bj said:
Idea is to use the natural backscatter properties of the atmosphere to make them omnidirectional.

[/ QUOTE ]
Some TV remotes are actually like this. The sensor is sensitive enough that you can point the transmitter almost anywhere in the room and it will work. Interesting idea here in that it would be like radio waves, but with the advantages of limited range (preventing enemy interception) and no EMI.