We all know that Li-Fi is a method in which LED is used for transmitting a high frequency content within an enclosed room, which effectively transforms the LED into a wireless transmitter as well as a light producing device.
For example Li-Fi concept can be used for transmitting and receiving a music data by using an LED as the light source and also a wireless music transmitter.
However the biggest challenge is to use a Li-Fi circuit for transmitting Internet data using ordinary parts and without involving complex and difficult to get components or MCUs.
In one of my earlier posts, I tried to implement a Li-Fi USB transmitter using opto couplers, however this design is capable of handling only single sided data, whereas Internet data involves complex, multiplexed, differential communication.
A USB connector basically consists of the following wiring details:
The +5V and ground are the supply out terminals which are normally used for powering the connected external device.
The +D, and -D are the data communication terminals which produces the complex differential signal across each other in a push-pull manner, meaning the +D is referenced to -D, while the -D signal is referenced to the +D terminals. This is what makes transmitting Internet through LED so confusing and complex.
This forced me to think of an alternative and more efficient design, that could actually transmit an USB internet data through LED Li-Fi circuit, without distorting the actual signal, and by employing ordinary components.
After some thinking I came up with the following circuits which hopefully would enable transmitting internet through LED light.
For the transmitter I decided to use a simple differential amplifier circuit module using IC BD5460, the following image shows the basic layout of this amplifier circuit.
I modified the design into the required Li-Fi transmitter circuit for making it compatible to internet signals, as shown below:
We can see how the differential music input terminals are used for receiving the internet data, while the output is connected to an LED via a bridge rectifier.
Using a bridge rectifier appears to be a smart idea, otherwise it would be simply impossible to transmit the push-pull signals through a LED, since an LED would simply fail to differentiate between these two signals.
By using the bridge we have effectively enabled the LED to recognize both the halves of the USB signal and send it to the receiver without causing any distortions in the original content.
The Receiver Li-Fi Circuit
Now the next challenge for me was to ensure that the rectified pulsating internet data through the LED is correctly decoded back to the original differential form in the receiver section.
This looked difficult however the simulation could be quite easily accomplished by using a dual supply based power amplifier circuit, for example the 100 watt mosfet amplifier already published in this website efficiently fulfilled the intended purpose as shown below:
The BJTs and the mosfets can be any general propose rated to work with 12V/1amp supply. However if you want a powerful decoded output you could very well keep the original values for the devices and enjoy a powerful LiFi decoded inernet output.
In the discussed concept we used a class D amplifier for
the LiFi transmitter, however a class D amplifier essentially involves PWM for processing the input, which could be highly undesirable for an internet data to go
through. We do not want to distort or modify the complex Internet data in any manner, therefore a class D amplifier perhaps cannot be applied for an internet LiFi.
As per my assumption we don't need a classD amplifier rather only a BTL amplifier, which does not involve a PWM function, an example design can be witnessed below using the IC TDA7052
Now this looks perfect, and seems like the Internet data would be transferred to the LED without going through any sort of artificial transformation.
To start with we can go with this 1 watt amplifier circuit as the Li-Fi transmitter and use a 1 watt LED at the output. The idea will confirm whether the proposed Li-Fi transmitter really works or not.
If you have any further doubts regarding this simple yet seemingly working LiFi Internet transmitter circuit you can feel free to express them in the below given comment box.