# help in electronic projecct



## mando (Feb 15, 2014)

Hi everyone,
I am working on an electronics project it's called VLC "visible light communication" i want your help to choose the LED "transmitter" with this specification 



*Bias voltage/ V 17.4 - 24.5


*Typical bias voltage/ V 22


*Corresponding typical bias current/ A 0.7


*Corresponding luminous flux/ lm @ 0.7 A 
driving current 380 - 540


*Corresponding typical luminous intensity/ cd 140


*Maximum bias current/ mA 1


*Maximum pulse current1/ mA 2


*Full viewing angle at half illuminance 130°


*Number of modules needed to illuminate 
the entire OMEGAshowroom2 @ 400 lx ~44 - 63


or something like this this specification for Ostar LE CW E2B-MYNZ N3P5 ..... i'm searching for product like this one or better can any one help me ???????

thx alot everyone


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## Steve K (Feb 15, 2014)

what wavelength? Do you have a receiver selected? That should define the wavelength that you are using. 

Once you've got a wavelength selected, then I'd start thinking about how big the transmitter can be, how big the receiver is, the distance between them, how much signal is needed at the receiver, how much light is needed out of the transmitter in order to achieve that signal level, ... and so forth. 
Oh... what sort of data rate you are trying to achieve, what sort of data format you want, is the data traveling in just one direction (from transmitter to receiver), or do want to send data back? There are sooo many questions that need to be answered.

A less important question... why visible light? There are a lot more receivers designed to work with infra-red light than visible light, especially for data transmission.


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## DIWdiver (Feb 15, 2014)

You've got a bit more work to do on those specs.

At 22V, 0.7A, you ought to get more like 1500 lm, not 500. 

You specified a max pulse current far less than the typical run current.

You want to illuminate the 'whole showroom', but how big is that? And what the heck does "~44-63" mean?


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## mando (Feb 16, 2014)

DIWdiver said:


> You've got a bit more work to do on those specs.
> 
> At 22V, 0.7A, you ought to get more like 1500 lm, not 500.
> 
> ...




really i don't know mean of this specification " optics isn't my specialization " 

whole showroom'~44-63" mean? this part isn't correct 

all i want to know the kind of led able to send data streaming carried by light to PD which distance between them is more than or equal 2m with data rate more than or equal 100 Mb/S and freq of this transmitter "led" is ~12 MHz .


thank you very much for your help ... plz help me as you can

thx Sir


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## PhotonWrangler (Feb 16, 2014)

It sounds like you're describing a Li-Fi system, correct?


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## DIWdiver (Feb 16, 2014)

Wow. If you want to send 100 Mb/sec on a 12 MHz carrier, you're way above the heads most or all of the folks here. I suspect you are on the wrong forum to ask questions like that.


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## Steve K (Feb 17, 2014)

I've done some work with modulating lasers many years ago. A solid state laser could be considered an upgraded LED, so the principles are the same. The difficulty is just that the LED is a relatively low impedance load, so it takes a driver with both speed and current driving capability. As a general rule, I'd say that a smaller LED will be easier to drive than a large one, so you'll want to analyze your communications link and figure out how much optical power you need, and select the LED based on that.

If any of these terms are confusing, then a lot of learning needs to be done before progressing further.

I'm also curious as to how a 12MHz carrier can be modulated with 100Mb/sec data. I would have thought that no carrier would be needed, unless you are counting the carrier frequency as being the color of the light. That would be quite a bit higher than 12MHz, though.


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## mando (Feb 17, 2014)

Steve K said:


> what wavelength? Do you have a receiver selected? That should define the wavelength that you are using.
> 
> Once you've got a wavelength selected, then I'd start thinking about how big the transmitter can be, how big the receiver is, the distance between them, how much signal is needed at the receiver, how much light is needed out of the transmitter in order to achieve that signal level, ... and so forth.
> Oh... what sort of data rate you are trying to achieve, what sort of data format you want, is the data traveling in just one direction (from transmitter to receiver), or do want to send data back? There are sooo many questions that need to be answered.
> ...






freq ~ 12 MHz but when i'm thinking i thought that i will need to know the transmitter first then receiver .
data rate or = 100 Mbs 
data which will be sent as ones and zeros depend on the turn on and off of the led
transmitter and receiver will be line of sight so data traveling in just one direction
i want to send data back but in fact i don't know how 


thanks alot sir


i'm really don't know how i can thank you for your help ... plz help me as you can


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## mando (Feb 17, 2014)

PhotonWrangler said:


> It sounds like you're describing a Li-Fi system, correct?




yes it's LiFi 

can you help me ??


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## mando (Feb 17, 2014)

DIWdiver said:


> Wow. If you want to send 100 Mb/sec on a 12 MHz carrier, you're way above the heads most or all of the folks here. I suspect you are on the wrong forum to ask questions like that.




what's the wrong with that ???


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## DIWdiver (Feb 17, 2014)

When the data rate is higher than the carrier frequency (or channel bandwidth) it implies some kind of fancy modulation techniques to achieve that. That would take a communications expert, not lighting hackers, nor even lighting experts.


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## PhotonWrangler (Feb 17, 2014)

mando said:


> yes it's LiFi
> 
> can you help me ??



The path of least resistance would be to locate an external ethernet media converter (10/100 copper to multimode fiber), remove the LED and use the existing driver lead to drive the gate of a MOSFET which can give you a higher current capacity. On the load side of the MOSFET it's just Ohm's law to calculate how much series resistance you need to drive the LED at the rated voltage.

The receive side is a little trickier as you have ti find a way to send the keystrokes and mouse clicks from the client back to the transceiver, which may or may not be line of sight.


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## DIWdiver (Feb 17, 2014)

It is by no means that simple. Getting a FET to switch at 100 MHz is no simple task. A simple FET-LED-resistor setup is not going to cut it. The phosphors used in most white LEDs will not switch at that frequency. The relatively enormous die size (compared to fiber LEDs) suggests capacitance could be a huge issue. Also, it's not likely that simple on/off modulation is used in such a device.

All this adds up to making the design of the transmitter far more complicated than flashlight drivers. If the OP were looking for a 100K or 1M baud link, it would be a different story. But 100M is a different world than 100K.


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## PhotonWrangler (Feb 17, 2014)

I'm finding FETs rated at 100mhz and beyond, but you're probably right about the limitation on the phosphor due to persistence as well as the shunt capacitance of a large die LED.


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## AnAppleSnail (Feb 18, 2014)

Well, it turns out that the finished product here would be the shining jewel of secure-area device linking, so this project is worth several million dollars to the right people (US Nuclear groups for one). I am not sure what it will cost to build as a prototype.

If you build your own receiver and transmitters, you can send data. Normal networking requires two-way communications. I would suggest starting small and building up. You are DEFINITELY starting at the wrong end, picking your LED before you have anything to drive the LED.

LED Phosphors take a bit over 100 ns to light. Non-phosphor LEDs do it about 5x faster. This gives a shortest-pulse rate of only 10MHz. Modulated pulses or modulated pulse length will be trickier. Most LED drivers will not respond in under 1 microsecond.

url=http://www.freetronics.com/blogs/news/10388341-send-data-using-an-arduino-based-li-fi-system#.UwNijc76R8E]Send Data - Arduino LiFi[/url]. "Arduino LiFi" would be a good place to start - It's a small microcomputer with a large environment of builders and sensors. There is a long way to go between wanting to do this project and having it done.


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## RetroTechie (Feb 18, 2014)

PhotonWrangler said:


> I'm finding FETs rated at 100mhz and beyond, but you're probably right about the limitation on the phosphor due to persistence as well as the shunt capacitance of a large die LED.


Capacitance _can_ be dealt with by increasing the drive power. But that's just a means to address this particular problem; it doesn't make it go away. Physical response times of the actual light-emitting material would be quite a bit harder to get around (if at all possible).



AnAppleSnail said:


> There is a long way to go between wanting to do this project and having it done.


More exactly: there's a long way to go between getting this working, and getting it working at a high data rate.  Just get something working at low switching frequencies (say, a few hundred kHz max). Then figure out what's needed to reduce switching times, but still have reliable detection at the other end.

As for 2-way communication: if receiver can see transmitter, then they can also see each other in reverse direction. Of course you'd need both transmitter + receiver at each end. Beyond that it's a protocol / signalling issue, not a technical problem. For ideas, you might want to have a look at 'one-wire', 2-way communication systems like USB, I2​C etc.


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## Steve K (Feb 18, 2014)

and a comment: my experience suggests that it may be easier/faster to just modulate the amplitude of the LED output as opposed to turning the LED on and off. Stopping the electrons in the diode and then getting them started is generally a more time consuming task than just reducing the current and then increasing it.

Doing this at 10MHz isn't breaking new ground. 100MHz could be tricky, especially if you need to do it for a large LED or a group of LEDs. Might need a bunch of paralleled drivers & LEDs, which would then require watching all of the delays and keeping them equal. 

Seems kinda pointless to try to do this with white LEDs. Not sure what wavelength would make a better transmitter, but I think the designer would want to find a suitable photodetector for the wavelength. I haven't looked at this stuff for a long time. Is there anything good for the shorter wavelengths?


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## PhotonWrangler (Feb 18, 2014)

For the receiver I would go with an integrated transimpedance amplifier / pin photodiode. This combines a picosecond-response sensor with a built in preamp / squaring circuit, and they're fairly cheap and readily available.


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## SemiMan (Feb 19, 2014)

What you are asking is definitely not a "project" but a commercial enterprise.

To that end, I have to expect that someone is going to get paid for the result, and to that end, one should be clear about that.

This is a hobbyist board and I don't mind giving fairly technical answers to hobbyists, but when I see such a request as the op posted, I can't help but think commercial and to that end, if you want "good answers" then ya needs to pay the "good money"  .... cause, while there are some good hints in the posts, nothing is there that is going to help you at all.

Time to hire a consultant.

Semiman


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## RetroTechie (Feb 19, 2014)

Ehm no... I think OP's requirements simply aren't realistic, *one way or the othe*r that isn't going to get done.

If some sort of commercial enterprise, OP shouldn't be asking questions here but be busy providing answer(s) to their clients. If unable, those client(s) should be hiring other consultants.


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## SemiMan (Feb 22, 2014)

The requirements are not unrealistic or unsolvable and as written are obviously a commercial specification. Good form on a hobby board is to state your question involves a commercial venture.


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## uk_caver (Feb 25, 2014)

Is it necessarily commercial?

It does rather seem to be the time of year for univeristy-projects, at least on some other sites I visit.


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## DIWdiver (Feb 26, 2014)

uk_caver said:


> Is it necessarily commercial?
> 
> It does rather seem to be the time of year for univeristy-projects, at least on some other sites I visit.



I absolutely agree. My first impression was of a senior project. As the OP appears to want to push the state of the art with very little understanding of the art, my inclination was to provide a reality check before providing assistance.

However, the suggestion that this seems like a commercial project is something that I can't argue against. And as the OP hasn't chimed in with a rebuttal, it appears to me case closed.

Regardless of whether the project is commercial or academic, the OP seems to have little understanding of what he's asking for, so I'm disinclined to put much effort into providing assistance.


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