[Jovan] is very excited about the possibilities presented by Visible Light Communication, or VLC. It’s exciting and new. His opening paragraphs is filled with so many networking acronyms that VLC could be used for, our browser search history now looks like we’re trying to learn english without any vowels.
In lots of ways he has good reason to be excited. We all know that IR can communicate quite a bit, but when you’re clever about frequency and color and throw in some polarizers with a mix of clever algorithms for good measure you can get some very high bandwidth communication with anything in line of site. You can do it for low power, and best of all, there are no pesky regulations to stand in your way.
He wants to build a system that could be used for a PAN (Personal Area Network). To do this he’ll have to figure out a way to build the system inexpensively and using less than a watt of power. The project page is full of interesting experiments and quite a few thesis on the subject of LEDs.
For example, he’s done work on how LEDs respond to polarization. He’s tested how fast an LED can actually turn on and off while still being able to detect the change. He’s also done a lot of work characterizing the kind of light that an LED emits. We don’t know if he’ll succeed yet, but we like the interesting work he’s doing to get there.
24 thoughts on “Hackaday Prize Entry: Cheap Visible Light Communication”
This could be interesting since one project log mentions LEDs meant for use in sunlight. If that’s the case, I wonder if this can be combined with optic for longer distance communications. I like the idea of a mesh network that can cover reasonable distances and can’t be regulated out of assistance. It will be interesting to see what [Jovan] can achieve with his project and what can be built from his body of work.
Always like the old Ronja project. 10Mbps Ethernet bridge with LEDs and $1 plastic lenses, <$100 in parts total. Kind'a wish a version for 100Mbps Ethernet had been made. tempted to take a crack at it myself…
There's also the Koruza project. http://irnas.eu/category/koruza/ It aims to leverage commodity SFP modules to make an inexpensive short range optical link. (~100M)
I wish Jovan luck. Competing with sunlight will be HARD without fancy optical filters, directional optics, or a low bit-rate modulation that can work with SNR << 1.
Problem with replicating Ronja for 100Mbps Ethernet is that 100Base-TX uses a 3-level level encoding (MLT-3) rather than straight binary which makes the optical driver and slicer more difficult if you are trying to do it directly. The other option is of course to go from RMII or MII and send the bits at full rate, but that’s a bigger problem.
Just a thought, without looking into Ronja too deeply (though I read about it a while ago), would adding extra frequencies help replace the multi-level encoding? As in several LEDs, different colours. There’s an option to use Ronja with red LEDs, perhaps an RGB one would be possible. The 3 LED chips will have approximately the same focus.
Hi, unfortunatly you get it wrong. It is not Ronja and it is not intended to even look like it.
Point of this project is to make costly hi-end sci. research meaningfull and posible for all of us mortals, and usable for low cost every day aplications.
Ronja has simular impact I hope to make when in early 2000’s they make low cost p2p longdistance IR/RedLED interconections, but all simularities end there.
We now live in age of IoT and we need large bandwith for all smartthing to communicate … so I hope this will spark Photonics tekecomunication in open air (LiFi) as next wireless of future.
That’s interesting, I’m curious if this could be expanded to something more than just point to point, where a transmitter/receiver could handle additional transmitter/receivers as long as they are within their field of field.
I figure that will require some sort of array of optical receivers and multiple wavelengths with an initial one used to negotiate the channels a new receiver can use for the array in a given FOV. It would be awesome to have a system where operators can just point their stuff in the right general direction to build out the mesh without having to have any sort of coordination with another station.
This is probably a dream but I can hope the tech marches towards this.
Hi Matt, right it dose. Point is to use OP.AMS in band-pass filtering mode so that environment light that do not pulsate at such a high speed will be pushed down. Soon I will put some newer pic’s that illustrate how transceiver work at ~8…10EV of daylight in room and at +1m distance with only 1x LED.
There is a newish LCD method that allows switching speeds of 30 nanoseconds, so if you could split white light from a xenon arc source with a diffraction grating then filter the spectrum with a 4K LCD design to operate at those higher speeds you could easily push out 20 gigabits per second via V.L.C., if you can find hardware to drive the LCD that fast. The LCD does not need pixels, only bands to match spectrum locations to shutter for the multiplexing effect. Best to only use the below blue and above red section of the spectrum due to gaps in the emission bands.
Just as a reference… (I know it is not the goal of this project), interesting to reading material:
In 1880 (that’s 136 years ago) there was the photophone https://en.wikipedia.org/wiki/Photophone
I also remember several Forrest Mims experiments using visible light for communications. Definitely not a new concept.
For entertainment read about Forrest Mims vs Bell Labs on this very subject.
if you want longer distance and visibility, go for laser diodes… they can be used nearly the same and have filters for each wavelength available cheap!
a bias tee is what you need to achieve high bandwidth, as on and off will suffer from inertia due to the I/V slope change where emission occurs… modulating between 60% and 100% brightness will be far more efficient
Coherent light sources have issues with self-interference and deep nulls when used in air as convective cells can be smaller than the beam width. LEDs don’t have this problem.
The stability of laser diode frequency is not a solid as people imagine, but this can be exploited to encode the data via FM rather than AM, which may allow for higher data rates that are possible by turning the diode completely on and off. Obviously a new form of receiver is required but beam deflection off a grating decodes the signal back to AM if you have a sensor with a graduated density window.
Good news: It’s been done as a standard – IEEE802.15.7, if I’m not mistaken
> He’s tested how fast an LED can actually turn on and off while still being able to detect the change.
Ah, well, but here he’s restricting himself to breadboard-style electronics. I know it’s not fair to compare commercial optical fibre modules with self-built VLC, but commodity hardware has been doing 40 Gigabaud for years now; so that means that, given a sufficient controller, you should be able to, in principle, modulate photon emissions at rates > 40GHz. Point is not that I claim he can do this with a bog-normal 20mA visible light LED (which technically *is* quite a bit different from the laser diodes in QSFP+ transceivers), but it shows that the limiting factor is certainly not the rate at which you can change the photon generation, but the quality of your LED driver.
It’s possible there’s a sharp cutoff, though, e.g. two types of LED, one “cheap” and one “fancy.” If this is the case, using “cheap” LEDs would be a huge step forward.
Hi, you are Absolutely right. As in any telecommunication it is essential to have good transceiver and receiver and same even in greater extent is mandatory in VLC. I was/am VERY limited by my own funds so I started research limiting it to something that any hobbyist even in small county like Serbia can afford. Best solution will be to use Resonant Cavity LED that have bandwidth (-3dB) of +2GHz (or even greater) but who can give 200,500…20.000$ on one RCLED, not including price of LED Driver for every day use?
I do not recommend LASER diodes because we do not want to pollute environment any more with eco/Eye hazardous radiation right?
I have some updates for this project/research regarding necessity to use Ultra fast OP.AMPs with bandwidth >1..3GHz that came only in SMD SOIC/SOT-23 needed for next step of near 200MHz direct modulation research. In short I will try to stay on breadboard as long as it will be possible prior to making leap to fabricated SMD board.
One reminder 200MHz of bandwidth can translate in 4Gbps using 16-Color Shift Keying (16-CSK) modulation suggested by IEEE 802.15.7-2011 on several channels :)
Line of sight…
I came down here just to say that. “line of site”? Really?
Right, just line of sight, for now, becouse bouncing of colored walls have filtering effect on color channel propagations that introduce to x more unknown factors. I have plans to translate MIMO with beamforming and propagation trening tehniques to VLC and to test how it will perform with color shifting bounce. Stay tuned, research will continue ;)
Do they even teach grammar any more?
Dragi “StopTheInsanity”, naravno da ne, engleski nije moj maternji jezik, ali ću biti korektan da Vam olakšam.
Ako se složimo da ovaj sajt promoviše tehnička rešenja kreativnih ljudi iz celog sveta koji su uz to spremni da Vam izađu u susret i koriste Vaš jezik, mislim da minimum pristojnosti nalaže da i Vi sa svoje strane imate razumevanja za razlike koje mogu nastati usled ne poznavanja jezičkog dijalekta koji Vi koristite.
U svakom slučaju Hackaday je tehnički sajt za kreativne ljude, a ne literarno-jezička sekcija ili “društvo mrtvih pesnika” …
Hvala na razumevanju :)
For translation you can always use Google translate :)
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