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Simple Comm System Using Visible Light Link

02/27/2017 4:28 PM

Hi

I want to build a simple system with the following specifications:

1. group of LEDs with high directivity as a transmitter and a photo-detector as a receiver (works efficiently within at least 1.5 m "5 ft").

2. the nature of the message to be sent is just a finite number of bits (maybe just 8 bits serially sent).

3. for the interface used in receiver, 7 segments LED display that shows a string of 8 bits whenever a new signal is received.

4. for the interface used in transmitter, 7 segments LED display that shows a string of 8 bits to be sent. Each bit has a simple specific switch that assigns the value of the bit (0 or 1). And a button that initiates the transmission of the string of bits.

5. high quality: error in detection is minimized as much as possible.

The problem is I don't know where to begin. I have a good background in the theory but I'm not familiar with the modules in the market.

What modules do you guys recommend to buy to build this system with the above specifications (would be convenient if it's available in Amazon)? What's the circuit diagram? any complicated programming to be expected (I want to avoid coding as much as possible)?

Thank you

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#1

Re: simple comm system using visible light link

02/27/2017 4:51 PM

Is this for a school project, general interest or for a job? What's the data signal representing and being used for?

You could do it with a couple of microcontrollers and a single LED and photo sensor, alternatively there are wireless development kits or complete products you could buy (again depending on what you want to do and spend).

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#2

Re: simple comm system using visible light link

02/27/2017 5:02 PM

A quick way to get started on this is by using a couple of Arduino Unos. Unos are cheap (under $25 each, less than half that for clones, R3-compatible Canaduino Uno Bone from Universal Solder sells for USD $6.05 to $9.101) and very versatile. Lots of material online covering various techniques for doing this, including using the LEDs themselves as photosensors in a half-duplex arrangement. As far as coding2 goes, many people offer their source code along with their project designs.

Have fun!

-----

1. I am in no way associated with this company or the sales of its products. Just a happy customer.

2. Warning: programming the Uno is highly addictive.

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#3

Re: simple comm system using visible light link

02/27/2017 5:31 PM

Adafruit1 is also a very good source. A little more expensive but a much broader offering. Plus, they have a forum if you've got questions.

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#4

Re: simple comm system using visible light link

02/27/2017 6:41 PM
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#5

Re: simple comm system using visible light link

02/27/2017 7:18 PM

Instead of 'high directivity LEDs' as a transmitter, why not modulate a laser diode for much greater directivity and range?

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#6
In reply to #5

Re: simple comm system using visible light link

02/28/2017 1:52 AM
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#8
In reply to #6

Re: simple comm system using visible light link

02/28/2017 6:46 AM

Come on guys: he only wants to transmit eight bits over five feet: I've never had any problems with my TV remote.

Why not just buy an infrared extender and hack into the cable at either end.

TV remote--------extender-------------TV/AV

██►----------◘█▬▬▬▬▬█►----------◘██

Cut extender.. ◘█▬▬//▬▬█►

Add interfaces.. ▒▒▬▬█►-------◘█▬▬▓▓

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#9
In reply to #8

Re: simple comm system using visible light link

02/28/2017 10:53 AM

Workable and awesome.

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#14
In reply to #9

Re: simple comm system using visible light link

02/28/2017 9:50 PM

The OP is not controlling a TV - he spelled-out what he's doing and it has nothing to do with TV remotes - and if you're going to bother using a cable at all, then why not use a five-foot cable and dispense with the optical link altogether?

I suspect Randall's post was made tongue-planted-firmly-in-cheek - and you fell for it hook, line and sinker lol.

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#18
In reply to #14

Re: simple comm system using visible light link

03/01/2017 7:28 AM

To be fair to Gutmonarch (a sentiment which doesn't come easily), I was being serious.

If you buy an IR extender for a couple of dollars, you get quite a lot of what the OP wants. In my original picture above I show the TV remote and TV, but, in the next I throw them out and cut out the middle of the cable; in the final picture I reverse the positions of the IR receiver and transmitter, so that you are left with two simple digital electronic interfaces to design.

OK I've skipped over the power supplies, but, the OP should be able to use supplies from whatever are at either end of his equipment.

Also I realise that some one designing this for production say would design the Tx and Rx interface circuitry. I just thought that this way would be much cheaper (mainly in time) for a one off.

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#7
In reply to #5

Re: simple comm system using visible light link

02/28/2017 6:41 AM

I disagree that the laser or hi-intensity diode (for optical cable communication) would be better for the introductory prj. -- coz of the possible damage to the diode from wrong driving control also coz higher precision/complexity of driving control setup -- on the other hand starting big makes the following prj.s a lot easier ???

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#10
In reply to #5

Re: simple comm system using visible light link

02/28/2017 1:46 PM

At 1.5m, an LED is more than enough even in variable light conditions (it's just a little hardware and software filtering, if any). In low light conditions, you don't even need a narrow beam LED and the data rate can be much higher.

Malware sends stolen data using PC Hard disk activity LED

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#11
In reply to #10

Re: simple comm system using visible light link

02/28/2017 4:36 PM

Now that's sneaky....he says taping his blinker...

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#12
In reply to #11

Re: simple comm system using visible light link

02/28/2017 4:44 PM

Reminds me of the cold war and their sneaky and sometimes bizarre intelligence gathering technique attempts.

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#15
In reply to #12

Re: simple comm system using visible light link

02/28/2017 9:58 PM

My fave Cold War spy trick is where they reflected narrowband IR light off a meeting-room window from, say, an apartment across the street, mixed the reflected, Doppler-shifted light with a bit of the original and extracted the audio transduced by the meeting-room window's glass pane.

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#16
In reply to #15

Re: simple comm system using visible light link

02/28/2017 10:21 PM

It's got nothing on my favourite, the Russian "Thing".

The Thing (listening device)

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#17
In reply to #16

Re: simple comm system using visible light link

02/28/2017 10:34 PM

Yeah, that's pretty sneaky. I vaguely remember reading about it as kid, but I didn't understand how it worked at the time.

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#19
In reply to #16

Re: simple comm system using visible light link

03/01/2017 12:34 PM

I worked several years for an "Agency" which had, and used, the original in our in-brief. It was some pretty machining, but I'm glad I had read about it in High School, and even wrote a paper on it, because I would have been lost trying to understand it myself, without that. But it was, and is, a pretty nifty device, and was WAY ahead of it's time.

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#13
In reply to #10

Re: simple comm system using visible light link

02/28/2017 8:43 PM

I'm going to suggest this technique to my Internet provider as it would probably triple their current speed.

On second thought, they'll probably charge me 20 times as much.

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#20

Re: Simple Comm System Using Visible Light Link

03/01/2017 6:58 PM

Thank you so much, guys. All your replies are enlightening.

I've changed my mind and decided to use a regular computer for interfacing in transmitting and receiving sides. It's simpler that way and I don't constrain myself to limited bits. I'm going to use two Arduino microcontrollers (one for the transmitter and the other for the receiver), laser diode, and a detector.

Two final questions:

1. What model "exactly" of Adruino do you recommend? something popular, reliable, and more importantly compatible to be directly connected to the laser diode & the detector. Should I pick something that supports high current pin to fulfil the 5 feet requirement? I want to avoid amplifying or any complications, compatibility is essential.

2. There are many types of laser diodes & detectors in the market. given the recommended controller, what brands and models should I pick that work best and still fulfil the 5 feet requirement?

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#21
In reply to #20

Re: Simple Comm System Using Visible Light Link

03/01/2017 7:56 PM

Two Arduino Uno R3s would be perfect for your project. Adafruit's laser diode draws only 25 mA, whilst the Uno's digital pins can source and sink 40 mA, so no worries there. You drive the laser diode directly from a pin. For your detector, you could use one of these photodiodes.

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Users who posted comments:

Andrew Westman (8); ci139 (1); comm engineer (1); gutmonarch (1); jack of all trades (4); micahd02 (1); Randall (2); SolarEagle (3)

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