Simple Li-Fi Circuit Using Transistor

In this post we are going to construct a very interesting project and this technology is just emerging in consumer electronics , here you will get hands on experience from this project.

You will be able to make your first fully functional analog audio Li-Fi circuit which can stream good quality music from your phone/mp3 player to speakers at home and you will be surprised how simple a Li-Fi system can get and you no need a million dollar laboratory to construct one, even a beginner in electronics can make this project with ease.

We will see:                   

• What is Li-Fi or Light Fidelity is?
• Is Li-Fi better than Radio Communication?
• Circuit Diagram of Li-Fi .
  
• Description of Li-Fi.
  
• Quick Video Demo of the Li-Fi setup.
  

Illustration of successful Li-Fi Transmission:

What is Li-Fi or Light fidelity?

Let’s clearly understand what exactly Li-Fi technology is before going in to circuit diagram.

Li-Fi stands for Light Fidelity, which uses visible light as medium for data transmission. The Li-Fi system consists of normal LED light bulbs and modulating circuits.

The idea of Li-Fi is to use existing light infrastructure to transmit data to our computer, Smartphones, tablets etc. This will eliminate some of the main limitations and disadvantages of traditional radio communication, such as Wi-Fi system that we use at home or office.

Li-Fi utilizes LED light bulbs which are connected to a modulating circuit which will convert incoming data stream into rapidly flashing light. We human begins can’t perceive the high frequency flashing light but we will perceive a steady room lighting without any flicker.

The receiver circuit can capture the high frequency flashing of LED and decodes it into understandable data stream for your computer or smartphone.

Now you would have got a basic idea what Li-Fi is all about.

Circuit Diagram for Li-Fi Transmitter:

NOTE: The above circuit diagram is copyright protected, the visitors/readers are NOT permitted to republish anywhere in any form. You can build this circuit for your personal purpose only.

Circuit Description:

The circuit is very simple; it consists of 3 transistors, couple of resistors, 3 electrolytic capacitors, one variable resistor and one 1 watt LED. The Whole circuit is configured in common emitter mode amplifier.

The three BC337 are connected parallel, that is base to base terminal, collector to collector terminal and emitter to emitter terminal.

There are two 1000uF input capacitors which allows only AC signal to enter the Li-Fi circuit and also prevents from 9V entering to your audio source/phone from the circuit.

If your audio source doesn’t have left or right channels, just connect ground to ground and connect the audio source to any one of the capacitor.

The 100 kilo ohm variable resistor is used for adjusting the LED brightness. The 1 Watt LED is used for transmitting the audio signal and light.

You should have been surprised by the simplicity of this Li-Fi circuit by now.

Receiver Circuit:

The receiver circuit is even simpler; make sure that you use a good sensitivity amplifier.

The 3V to 6V solar cell can be used as light sensor, you can use a good USB computer speaker to receive audio or you can use any amplifier with good sensitivity.

You should be getting very good sound quality and the LED should stay solid ON regardless of the audio input and LED should not flicker while transmitting signal.

How this Li-Fi Circuit works?

The Li-Fi circuit serves two purposes:

• Room Lighting.
• Data transfer.

While designing a Li-Fi circuit one must keep these two requirements in mind. Now consider the first requirement which is room lighting.

The circuit must provide a steady lighting and must not flicker due to data transfer or the flicker rate must above our eyes persistence of vision while transferring data. The circuit proposed here has negligible flicker and always produce a steady brightness regardless of data transfer and still manage to transfer analog and digital data.

You might wondering how can we transfer data without change in brightness? Actually there is very very small change in brightness of the LED. The difference between maximum and minimum brightness of the LED is not perceivable to human eye because the difference is extremely small. The difference in the brightness can be detected by a solar cell easily, this can be witnessed by hooking a oscilloscope across its terminals and we can see the waveform peaks few millivolts.

The millivolts peaks from solar cell must be amplified adequately using a USB computer speaker or any other good sensitive amplifier so that it can drive a speaker. To keep the circuit simple as possible (to avoid multistage) of the transmitter, we have connected three low power transistor in parallel so that it can drive 1 watt LED with adequate current.

The 4.7K and 1 K resistors provide necessary DC biasing for the three transistors which will put the transistors in active mode where the transistors acts as amplifier.

If we over bias the circuit with lower resistor values, it will put the transistor in saturation mode where the transistor fully ON and does not respond to the input. If we under bias the transistors it will go to cut-off mode where output current will be too low to drive the LED ON.

We can spot the 4.7K resistor is connected in series with 100k variable resistor, this is to adjust the quiescent current of the amplifier (transmitter) thus adjusting the brightness of the LED.

Quiescent current: Quiescent current is the current consumed when the circuit performing not work.

The quiescent current in the circuit is the reason why the LED stays ON regardless of the audio input. We have used the quiescent current to our advantage to glow the LED.

That concludes the working of this circuit.

Components List:

• 3 x BC337 NPN Transistor
• 1 x 4.7K resistor
• 1 x 1K resistor
• 3 x 1000uF/25V electrolytic capacitor
• 1 x 1 Watt LED
• 1 x 100K Variable Resistor
•  1 x switch
• 1x 3V to 6V Solar cell       

Prototype Images:   

Below are the important points to be noted if you are doing a PPT / presentation in your  college / school or just curious about Li-Fi technology.

Is Li-Fi better than Radio Communication?

In this section we will understand some of the limitations with traditional radio communication such as Wi-Fi and how Li-Fi will be a good replacement.

The Limitations/disadvantage of Radio communication are:

• Radio Waves have Limited Bandwidth.
• Cannot be used in some restricted areas.
• Security.
• Health Hazards.

Let’s explore each of them.

1) Radio waves have limited bandwidth:

Radio frequencies range from 3 KHz to 300 GHz. The radio frequencies are classified into many categories like Low frequency, Medium Frequency, High frequency, Ultra High Frequency, Extremely High frequency etc. Each of them is allocated for specific applications.

For example FM radio signal is allocated from 88 MHz to 108 MHz and AM stations from 535 KHz to 1905 KHz.

Due to increasing of wireless devices per person and emerging of internet of things (IoT) devices, allocating the radio frequencies is getting tighter day by day and licensing the radio spectrum costs enormous.

We have something called ISM band which stands for Industrial Medical and Scientific band, the devices operating at this frequency don’t need be licensed by the users. The best example is your Wi-Fi router; it operates at 2.4 GHz and also 5 GHz.

Do you feel that your Wi-Fi internet is slow at times? If yes, then you are probably living in an apartment with many of your neighbor using Wi-Fi.

Wi-Fi routers mostly operate at 2.4 GHz range and some high end routers operate at 5 GHz. Due to the interference of many Wi-Fi signals from you and your neighbour’s router, the data transmission gets slow down than your wired connection.

Due to this congestion router manufactures are introducing 5 GHz band to avoid such Wi-Fi congestions, but with 5 GHz you will get shorter range, yet this is not a full solution for our future needs.

2) Restriction of Radio waves:

Radio waves are restricted in many areas such as hospitals, operation theatres, airplanes, research facilities etc.

You cannot always enjoy Wi-Fi internet in a hospital or in an airplane or in a place where the radio communications are restricted, because there could be interference with sensitive hospital equipments, which treats valuable patient’s life or very expensive experiment and interference of radio waves could alter the results.

So not everywhere radio communications are permitted.

3) Security:

Guess what is the worst thing can occur to your wireless internet, is it disconnection of your internet? No, it is your network getting hacked by someone else!

Wi-Fi can penetrate through walls and surround you area, you may say that my Wi-Fi is secured with a password but, a skilled black hat can break in to your network without any notice, and many of you are not good at setting a strong password for you router.

4) Health Hazard:

High energetic radio waves are suspected to cause health issues; there are some people who complained that they are affected from high energetic radio waves.

But there is no documented evidence to support the statement that radio wave causes cancer. May be science yet to discover the health hazards on human begin and animals and even plants.

Now, let’s see how Li-Fi can overcome these limitations:

1) No Bandwidth Limitations and Interference:

The Li-Fi has bandwidth at least 1000 times greater the radio waves; this can handle the future internet needs with ease.

No interference with neighbour’s internet connection as your internet will not go beyond your room and neither other’s internet will enter you room.

Very high data transfer speed compare to Wi-Fi, researcher calculated theoretical maximum data transfer speed of 224 Gb/s isn’t that mind blowing?

So, now you have very high speed data connection without any interference.

2) You can access Internet anywhere:

Radio communications are restricted in some area, guess what is not restricted? Visible light!

Now we can restore the access to internet in airplane or in hospital or in research facility without worrying about radio transmission interference.

3) Security is enhanced:

Now the internet will not go beyond your room as the light from your room will not leak like Wi-Fi and black hats will have tougher time to hack your network.

To access the network the black hat must be physically present on your room and you know what to do next if such unknown person present in your room.

4) Reduced Health Hazards:

We are using visible light since discovery of fire; visible light spectrum has little to no health hazard. LEDs don’t contain any mercury or other toxic chemicals present in like CFLs, which also emits small amount of ultraviolet rays, and yet CFLs don’t cause health hazards, so we can say that LEDs are one of the safest light sources available.

In conclusion we can say that Li-Fi is superior to traditional radio based communication, but Li-Fi may not be without its limitations or disadvantages which may be yet to discover.

Video demonstrating Li-Fi circuit: Watch it full screen.

If you have any questions reading this project, feel free to express in the comment section you can anticipate a guaranteed reply from us.