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How to make simple a LI-FI (Light Fidelity) Circuit

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LI-FI is buzzing around the Internet since past few years; recently LI-FI is gained more popularity around the internet and developers. LI-FI stands for Light Fidelity which was coined by Harald Hass.

By: Girish Radhakrishnan



Circuit Objective

The objective of LI-FI is transfer data through visible light. Since the bandwidth of visible light is 10,000 times more than Radio waves, more data can be transferred through light at short period of time.

Visible light communication (VLC) eliminates the risk of some disease caused by the Radio waves due to long period exposure.

This protocol can be adapted where Radio waves are restricted, such as airplanes, hospitals, and in some research facilities. Researchers reached bit rate of 224 GB/s which is 100s of times faster than our average WI-FI connection at home or office.

This article explains about the basic idea how to make a very simple LI-FI circuit in which we will be able to transfer any audio source through light and receive it from the receiver which is placed few feet from the Transmitter.

Here explained about analogue communication through light, where as original LI-FI system uses digital communication, which is more complex and difficult to make one at hobby lab. But the concept is exactly the same.

 

Here is a simple block diagram explaining LI-FI:

 

The Circuit Design:

The circuit consists of two parts, which are receiver and transmitter. The transmitter consists of 3 transistors and few passive components paired with 1 watt LED. Which will changes its brightness with respect to audio signal.

But changes in brightness due to audio signal will not visible to human eye. We only see static illumination of white LED. The receiver consists of a photo detector (here I used solar cell) which is paired with an amplifier. The sound output is given by the speaker.

The transmitter is transistorized amplifier which consists of 3 amplifiers connected in parallel to drive the 1 watt white LED.

Each transistor base consists of voltage divider which gives necessary bias for the individual transistor. The input stage has capacitors at each transistor’s base for blocking DC signals which could degrade the quality of output.

LI-Fi Schematic

 

Update: The above design can be also tried using a single transistor as shown below:

 

 

You can use a current limiting resistor series with LED if you want operate the circuit at higher voltage (say 12V).You can also use standard 0.5mm white LED with current limiting resistor. For an audio source you can use mp3 player, mobile phone or a microphone with pre-amplifier etc.

The receiver consists of a 6 volt solar cell (3 volts above works fine) in series with 2.2uf capacitor which is paired with an amplifier. The amplifier need not to be the same illustrated here, but you can use any amplifier lying around your house. But make sure it as good sensitivity.

Amplifier Schematic

 

Here is author’s prototype

Video Clip:

You can use any amplifier with good sensitivity for receiver part. To test this circuit, go to a room where ambient light is dim and make sure no nearby electrical light source.

Place the 1 Watt LED parallel to solar cell. Turn ON the power supply for both transmitter and receiver, give audio input to transmitter, adjust the volume to transmitter. You can here clear audio sound on the receiving speaker.

The above explained Li-Fi circuit can also be tried using a photodiode as shown below, where the amplifier section is replaced with a LM386 amplifier circuit:

UPDATE:

Some Important Notes and Considerations Regarding the above Li-Fi Circuit

In this Li-Fi the LED does flicker, but it is in-significant for our eyes to detect.

If your eyes can detect those flickers, something wrong with the build.

The change in the brightness of LED due to the audio input is very small, but there is change in the brightness, where our eyes can’t detect.

If there is no audio input, the LED stays solid ON, the solar cell produce some voltage. The input capacitor at receiver blocks those DC signal giving almost zero voltage to amplifier.

When we apply audio signal at transmitter there will be change in the LED’s brightness (Very small). The solar cell replicates the small varying voltage, the capacitor will allow the small variation in voltage amplitude to amplifier and rejecting strong constant DC voltage.

The amplifier must have good sensitivity since the input is feeble. Probably that’s why many readers are commenting on loudness of the audio.

I have used old-school home theater’s amplifier which had very good sensitivity and the resulting output was LOUD and CLEAR.

- Girish Radhakrishnan

Reader Interactions

Comments

  1. hi swag …can i send data more then 1M mebe text file or a picture for 2meters ..and can i buy it and export the circuit
    for iraq

    Reply

  2. sir,
    i’m a final year undergraduate student working on applications of li-fi: indoor positioning using lifi. can you please tell me how to use this circuit for positioning.
    and what is the distance between tx and rx to be placed

    Reply

    • Sunil, as long as the light sensor is able to receive the light from the LED it will work, the distance will not matter, but you will make sure that no other ambient light reaches the sensor…

      Reply

    • Gajendra, solar cell will be easier to configure, photo diode will require some technical consideration…so solar cell is the easier option.

      both are equally good as far as results are concerned..

      Reply

  5. Hii swag
    I make lifi Circuit same as your Circuit diagram from above. But from wheres i will provide power supply i dont know,
    Means R1 connect to +ve and R6 connect to -ve of battery ??

    Reply

    • Om, the Vcc line is the positive, and all the wires linked with this line are positive.
      similarly all the wire links joined with the ground symbol are negatives.
      use 5V as the supply

      Reply

  6. hey there can u briefly explain the working of ur reciever and the components needed. I have a preamplified speaker and it a has 3.5mm jack input., Can i directly connect the solar panel to it?

    Reply

    • hey, yes you can connect the solar module directly to the input of your amplifier circuit, but make sure no ambient light reaches the solar module except the light from your Tx LED.

      Reply

      • It won’t work if any other form of light reaches the light sensor of the receiver, because after all the light sensor is an ordinary light sensor and get activated with all forms of light.

        Reply

            • yes for a1.5V LED you can use anything between 1 and 6 LEDs with a 9V battery, a resistor will be required if the LED count is less than 6

          • thanks again swag .You are very helpful. I am almost done making the project. Now I need to finish the receiver part .I have solar panels from 2 calculators that I scavenged. Will that be enough to run the receiver?

            Reply

          • The transmitter circuit started working as soon as I connected the battery. The LEDs lit up and stay ON with or without the music signal from my phone. Does this mean that it’s OK?

            Reply

          • Hey Swag, the preamplified speakers I told about in one of the previous comments are my old computer speakers which have an amplifier inside and a 3.5 mm jack coming out of it.

            Reply

            • that’s fine ATR, just touch the 3.5mm pin tip, if that makes a loud noise on the speakers then your system is ready for the solar chip integration, which can be connected across the 3.5 mm jack’s relevant inputs.

          • hey swag the setup worked …I am getting audio output but i think the speakers are not good enough because the sound is very grainy.

            Reply

            • That’s awesome ATR, the issue could be perhaps due very feeble output from the solar module, you can try adding a LM386 kind of amp in the middle to boost the solar chip output and then this could be fed to the amplifier for the final amplification, just a suggestion though!

  7. sir ,
    I am a student i have been working on lifi but i am facing an error that if we use white or green or any other led than the sound is coming very low It is coming loud on red led only.

    Reply

  8. Hi,

    Thanks for your follow up. I have sorted out the problem and now it transmits quite well.

    Now please let know how to use Laser in place of the LED. Would replacing LED with Laser work?

    In the circuit LED terminal voltage is 3.3v and I presume Laser needs 5v so would it work if replaced? If not then suggest. I am using 9V to powerup the circuit.

    Reply

  9. Hi,
    Like the article very much and I did a experiment also. But as I didn’t get the proposed transistor so I used BC338 instead of BC337 in the transmitter and also a 6v Solar Panel instead of 3V Solar Cell in the receiver part. Please let know what would be the drawback in it’s performance?

    I am experiencing very very low signal. Is it due to the Solar Panel I used or for the BC338?

    Reply

    • I am glad you liked it.

      the transistor can be any small signal transistor such as BC547 or 2N2222, and 8050 will also do.

      make sure the LED lights up optimally during the presence of a music signal and shuts down completely in its absence…and also make sure no other light except the LED light falls on the light sensor. alternatively you can also try the LM386 circuit with an LDR for a more responsive performance.

      Reply

      • Hi,

        Thanks for quick reply.

        I used BC338. The LED is always on even when there is no signal applied to it. Is it a problem? Would using BC547 gives better output than BC338. Though BC338 giving good LED Illumination.

        I used 6v Solar Panel with 2.2 capacitor and fed to amplifier. The Signal received is very very low. I have to put full volume to hear some output.

        Is it due to Solar Panel or due to BC338? Please help in the issue.

        Also I do not have Solar Cell and nor could get Photodiode. What modification needed to use LDR to existing amplifier if I have to replace Solar Panel? quick help appreciated as I am sitting with LDR in hand.

        Reply

        • Hi,

          I thought the LED would be always ON and audio would be transmitting through it.!!!!

          In one of your comments I read
          “I guess you are referring to the first circuit in the above article, yes the LED will be lit while no signal is connected to the circuit, but as soon as you connect the function generator, the negative signals from it will begin shutting off the LED at the specified frequency rate and you will start seeing the required conversion from the LED.”

          So I assumed the LED would be always on.

          I was using 3 BC338, 1 Watt LED in the transmitter. In the Receiver end I was using 6v Solar Panel 300mA along with capacitor and A House Amplifier.

          I did get audio signal to my amplifier but it is very very low even at full volume.

          If my building has error or has to change the transistor then Please suggest a Circuit where LED would be always ON – With Signal or No Signal.
          I would like to have my room illuminated always (with Signal or No signal) and also have Music transmitting when Signal fed.

          Reply

        • HI deepak,

          LED stays SOLID ON even when no signal input is applied to transmitter that’s the property of LI-FI:- Light and also Communication. Our eyes can’t pickup the flicker due to input signal. If it flicker probably no sufficient power to transmitter.

          Regards

          Reply

          • Hi Girish,

            Can you please briefly explain how will the LED respond to positive music peaks which may be above 0.6V, because the LED is already ON through R2?

            Reply

          • OK, I think I got it, higher voltage pulses will push proportionately more current to the base of the transistor and produce equivalent change in the brightness.

            Reply

          • Hi sir,

            The LED does flicker, but it is in-significant for our eyes to detect.

            If your eyes can detect those flickers, something wrong with the build.

            The change in the brightness of LED due to the audio input is very small, but there is change in the brightness, where our eyes can’t detect.

            If there is no audio input, the LED stays solid ON, the solar cell produce some voltage. The input capacitor at receiver blocks those DC signal giving almost zero voltage to amplifier.

            When we apply audio signal at transmitter there will be change in the LED’s brightness (Very small). The solar cell replicates the small varying voltage, the capacitor will allow the small variation in voltage amplitude to amplifier and rejecting strong constant DC voltage.

            The amplifier must have good sensitivity since the input is feeble. Probably that’s why many readers are commenting on loudness of the audio.

            I have used old-school home theater’s amplifier which had very good sensitivity and the resulting output was LOUD and CLEAR.

            I would suggest you past this comment in the article as update, if possible.

            Regards

            Reply

            • Thanks Girish,

              Yes since the response of the music pulses will be extremely rapid, the output cannot be detected by our eyes and we will be able to see a constant average illumination, but the solar cell and the amplifier will be able to extract the minute variations and reproduce it into the exactly same data as the input over the loudspeaker.

              Actually the placement and the selection of the 2.2uF capacitor is interesting and crucial which helps to effectively vary the current into the base of the BJT which in turn causes the LED to change its illumination pattern as per the music, and since the BJT is a current controlled device becomes perfectly suitable for the application.!!

              I’ll add your comment soon in the above article!!

  10. hay Swagatam Majumdar.

    Thank you so much for explaining allots of things.really nice of you budd..

    i doing my final project on LIFI in general and i need any demonstation on Matlab

    do you think you can help.

    this is my facbook and email.

    Sid Majdali
    s.majdali@yahoo.com

    Thanks in advance

    Reply

  12. Thanks for your response,i want to be specific reason with what I will be buying in the market for the project.
    Please give me the specifications to save me the stress of mixing things up.
    Thanks

    Reply

    • what exactly do you want to make using LiFi, I mean what kind of frequency do you intend to communicate with? please provide a detailed view

      Reply

    • Good Morning,
      I used Proteus to simulate the transmitter circuit and it worked with a sine wave generator as the input.
      But during the implementation it did not work and when I later changed the input to an audio file,the led was not coming on.
      The receiver circuit is not working as well,will appreciate it if you can guide my through.
      My defense is next month and I haven't gotten to anywhere,though audio transmission using LiFi is cheap to my Lecturer as a final year project work,will as well appreciate it if you can recommend something better to me and guide me through it.
      Look forward to your speedy response,time is not on my side again

      Reply

    • It did not work because your implementation is incorrectly done.

      if the LeD is not illuminating it simply means that your circuit is not biased correctly….and if the LED does not illuminate then how will the receiver respond?

      either you must elevate the music input power or enhance the BJT stages in order to increase its sensitivity which perhaps can be done by converting the BJTs into Darlington pairs.

      you can try the above suggestions.

      Reply

  13. Wow i am blessed by the wealth of knowledge here,had to read through all the comments, weldone sirs.
    I am a final year student from the department of Electrical and Electronics Engineering in Nigeria,Want to use Lifi Technology as my final year project work. I am only acquianted with the theory but i need help and guidance with the practical implementation.
    will appreciate it if i can get help and support from these, you can do well to connect with me on aroloyefolajimi@gmail.com.
    Look forward to your response,thanks

    Reply

    • Thanks Aroloye, complete practical implementation is already explained in the above article, if you have specific questions you can feel free to ask me here, I'll try to solve it….

      Reply

  14. I have connected the circuit and did not work so I drew it using the Livewire program but stopped the subject at the income I did not understand what the value of the income supposed to be in order to operate the circuit Note that I want to be a graduation project has been suspended in this section I hope you help me and thank you very much

    Reply

  18. The circuit works fine for frequency less than 7-8KHz square wave. It will start distort beyond that. Will you please tell me a circuit which work upto nearly 500KHz. Thank you

    Reply

  19. Sir, myself Sujit Chatterjee. I am working on LiFi since 2016. I have to transmit signal 100Hz-1MHz square wave via LED. Whether the mentioned circuit will work for that range….

    Reply

  20. I was wondering if a setup like this using infrared would mitigate the problem of light interference from ambient light? The lights in my room are all LED. Also, what are your thoughts on stereo? Would a stereo setup require some micro-controller circuitry?

    Reply

    • yes that's possible, but the advantage of using LED is that you are able to illuminate a given space while also transmit the data….IR won't fulfill this twin function.

      for stereo you can use a pair of these set-ups but the signal will need to be modulated through a carrier signal within the two sources, otherwise the two lights could interfere with each other.

      Reply

    • I would prefer to use visible light, however my lights are above me on a ceiling fan. To achieve using them I would have to devise some sort of PLC to the LED and then modulate the LED for the Li-Fi. That is WAAAY beyond my abilities so I thought since remote controls use infrared in bright conditions it might offer a solution with less interference. You said infrared is possible, but do you think it would be less affected by ambient light with the right components?

      Reply

    • remote controls use a specific frequency and therefore ambient light is not able to affect its functioning, but for music the frequency range cannot be restricted and that could be a problem….
      to counter this, the IR receiver sensor may need to be covered in such a way that it is able to receive the music signals from the IR transmitter but remains hidden from the ambient light.

      Reply

  24. you can probably implement it by using two of these amplifier circuits, one as the Tx, other as the Rx.

    In Tx input join the 6 signal via diodes, at the output side connect two LEDs in parallel with opposite polarities (anti-parallel)…make sure each one has its own 1K resistor.

    At the Rx input connect an LDR.

    Reply

  25. Sir I am working on data transfer through rj45 connector…basically I want to convert 6 pin to 2 pin and give it to LED and then decide and convert again 2 pin to 6 pin…sir how can I do the transmission section please help me

    Reply

  28. Hey ! It works for me ! But i have a few questions:

    What's the name of that type of system ?
    How did you find those values of resistor and capacitor ?
    Which calculations did you do ?

    Thank's !

    Reply

  31. i feel sorry for you having to answer all the stupid questions you get on this site. you should setup some ground rules for not answering questions that could be answered by a simple google search and 10 seconds of time. The comment sections are just filled with stupidity and ignorance because you bother to answer questions like, "sir, i am working on the research project on lifi so please provide me more information regarding lifi." Seriously, don't answer that shit. It makes this site, which is filled with great information, look stupid as it is catering to the worst form of ignorance. If you want to help them, help them to realize it is quicker and more efficent for them to type nearly the same thing into google and find the answer and much more. If he would type "information regarding lifi" into google he would have got the URL you shared and a ton of other information. Now he has to come back and ask "where can i get more information about lifi" because you didn't teach him to learn, you just babied him and gave him the answer which is like cheating in school. This site is a great place to learn, but the comments are a great place to want to kill yourself over stupidity.

    Reply

    • I appreciate your suggestion, and I quite agree with you.

      eventhough I too prefer skipping such questions I finally end up answering them just to make sure nobody gets hurt and feel ignored.

      Reply

  32. Sir, I am an IT student don't have much knowledge about electronics. Can you pls answers my questions.
    To my knowledge we Input internet connection through a ethernet cat 5 cable. The analog signal will be converted to light bean and the receiver will receive the light beam and convert them to analog signals which can be fed to a laptop againa via cat 5 cable.
    But I dnt see any ethernet cable socket in the diagram.

    Reply

    • Hi THO, sorry for late reply,

      Yes, the LI-FI is bi-direction communication, in this post I just showed, how to make a one way communication, so that even a beginners able to accomplish with ease.

      In a real LI-FI system the down-link (download) is visible light, the up-link (upload) can be infrared or different wavelength of light or time division multiplexing.

      The circuit given in this post is a analog, no acknowledgement need to be fed-back regrading missing information while transmitting, but in digital system the missing bits need to be send again, this is only possible with up-link.

      Regards

      Reply

    • The LI-FI shares near fiber optic concept, the bits are modulated through light, the light travels long distance with out leaking the light out of the system. But in Li-Fi we intentionally spread out the light for short distance from an access point.

      The key difference is that fiber-optic, light propagates through the fiber. In LI-FI light propagates through air medium.

      Reply

    • The simpliest way I presume it would be having the same couple of circuits on both sides, as as transfer and receiver at the same time. In that case you would have to need a controller device capable of responding to whatever signal you are sending after evaluating it.

      Reply

  42. Thank you so much sir. It worked fine for me, but the volume is really low. Ill try and change the speakers.
    for the transmitter part can we use 9v Vcc instead of 7.5v?

    Reply

    • I am glad it worked for you Ananth, yes 9V can be also used instead of 7.5V.

      you can try a better amplifier design for improving the sound quality

      Reply

  43. Hello sir, I have designed exactly the same circuit as yours, but i am using function generator instead of Audio in. But i am getting more than 8 volts output. Can you please help me with that. Which components should i change or is this circuit only for supplying audio signals? I need to ask one more thing that we are supplying positive VCC directly to LED terminal, is it fine?

    Reply

    • Hello Abdullhaq, the circuit can be use for transmitting all kinds of frequencies, so it should work with your function generator output also, first make sure that your function generator output has only pulsating DC and no constant DC…and the solar cell gets no other ambient light except the function generator frequency light

      Reply

    • Thanks sir, But how should i limit the output voltage to around 3.2Volts that can be handled by LED. Because i am getting more than 8 volts output even without attaching function generator.

      Reply

    • I am assuming you have connected the LED with the function generator output, in that case you can connect a resistor in series with the LED to limit current and optimize the volts automatically, however if this 8V is constantly available then that's incorrect and your function generator could be faulty according to me.

      alternatively you can connect a 10u/25V capacitor in series with the LED resistor…and a another 10K from LED/capacitor junction to ground.

      Reply

    • …sorry I think I got you wrong, I guess you are referring to the first circuit in the above article, yes the LED will be lit while no signal is connected to the circuit, but as soon as you connect the function generator, the negative signals from it will begin shutting off the LED at the specified frequency rate and you will start seeing the required conversion from the LED.

      Reply

  44. connected a stereo jack (3.5mm) to the radio. I connected the ground pin of the jack to the cathode of a small LED. The left channel pin was connected to the anode of the LED. In addition, I connected a 9V battery with a 1k ohm resistor to the anode and cathode of the same LED. This was my transmitter circuit.

    In the receiver circuit, I simply connected a solar panel (6V) to the speaker. I powered the speaker through wall socket (230 V AC current). It worked. I was able to transmit audio.

    Now, I want to be able to transmit a video, in the same way you did in your TED talk a few years ago. This time, my input is an AV jack from an old DVD player. I connected the ground wire of the AV cable from the DVD player to the cathode of LED and the positive wire to the anode of the LED. In addition, I connected a 9V battery with resistor to the LED. As above, I connected the solar panel (6V) directly to the AV cable of a mini screen which takes AV input. The screen is powered by a wall socket.

    This time however, nothing shows up on the screen. I tried using an LED of higher brightness (1 watt). Now, only an icon shows up on the screen which says "AV 1 detected" for a short while and then disappears altogether.

    I would be obliged if anyone explained to me how you achieved video transmission through Light Fidelity.

    Reply

    • appreciate your efforts, however a video signal cannot be transmitted through a LED so easily, because a video signal may have many complex frequency data embedded together which cannot be transmitted or received without special encoders and decoder circuits. Music is a single frequency data therefore it may be much easier to send music through a Li-Fi circuit, but not a video signal

      Reply

  47. How do you found the type of tranizstors (example: BC337) and the values of resistors and capacitors?? I have a same project in my tecnhological institute so the circuit suits me but…the professor will ask me how i found the values of the components (example: Why 4,7kΩ resistor and wjy not 2kΩ??)

    Reply

    • Hi spyros,

      I found the resistor values by trail and error method. I used different values of resistor and I found the above specified values optimal. Initially I chose BC548, but too weak to handle 1watt LED, so gone with stronger transistor BC337 these info can be found in the datasheet.

      regards

      Reply

  49. Sir, if I am giving a signal from a signal generator to the input should I do any changes in the transmitter . If yes can you plz tell me those changes. Thank you

    Reply

    • Amarnath, no changes would be required for the signal generator signal, it's also a kind of frequency so will work just as a music input is supposed to work

      Reply

    • Thank you sir, I was able to give the input via a signal generator but it seems I'm only able to transmit and reciece square waves.. Other waves(above 0.016V) are saturating the output.. If I decrease the gain of the OP amp will it work ?
      Thanks again

      Reply

      • Hi Amarnath, the gain of the shown LM386 amp circuit is already set at the max 200 range.

        you can probably try to optimize the volume control for getting improved results, and reduce distortions.

        Reply

    • In the common emitter mode you will get square wave pulsed waveform, while in the common collector mode or emitter follower mode you will get an exact replica of the fed music… reinforced with higher current

      Reply

  54. We have made the transmitter and receiver as mentioned.
    We found that the data is getting transmitted through led but we aren't able to receive that using solar panel ie. The voltage drop across solar cell remains almost constant
    Now what shall we do to increase sensitivity of the panel?

    Reply

  56. May I know the specifications of the amplifier?
    Will any audio amplifier do?
    Is it necessary to modulate the input?
    I am in first year of engineering and doing this circuit as my project, so would you please guide or suggest any modifications to the circuit?

    Reply

    • any audio amplifier can be used for the conversion.

      modulation will result in a better and a stable Light output from the LED but the circuit design could be a bit complex.

      Reply

    • The concept is dead easy and you won't need anything complex for a basic design as above, however in the above design the light would fluctuate with music so it must be superimposed on a carrier frequency and then transmitted. the receiver side would also need a circuit capable of extracting the superimposed music from the carrier signal for the expected LiFi output

      Reply

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