Professor Harald Haas, a Mobile Communications Professor at the University of Edinburgh, invented a new technology called Lifi. The vision is that a Li-Fi wireless network would complement existing heterogeneous Radio Frequency (RF) wireless networks, and would provide significant spectrum relief by allowing cellular and wireless fidelity (Wi-Fi) systems to off-load a significant portion of wireless data traffic. Unlike wifi, Lifi communicates data through light instead of radio waves, using any visible light source for communication. Because of the availability of a huge license-free spectrum of approximately 670 THz, it has the potential to provide wireless links with very high data rates. The technology is based on the modulation of light with a data signal, achieved by switching LEDs on and off at very high frequencies to create pulses.

The widespread availability of cost-effective electronic components such as Light Emitting Diodes (LEDs), photodiodes, and cameras has played a crucial role in the development of communication systems using visible light. This technology leverages various properties of light to encode digital data. This encoded data is then modulated and transmitted over short distances to the receiving end. Photodiodes are a particularly attractive option due to their affordability and straightfor- ward implementation. Meanwhile, LEDs have emerged as the preferred light source for LiFi technology. This preference is attributed to their global accessibility, energy efficiency, and durable characteristics. LiFi serves a dual purpose by not only offering illumination but also facilitating data transfer. It accomplishes this by generating digital sequences composed of different combinations of 1s and 0s through the toggling of LEDs on and off. In our paper, we emphasize the use of Li-Fi communication for data transfer through the Pulse Width Modulation (PWM) technique. This approach employs a laser diode as the transmitter and a Light Dependent Resistor (LDR) as the receiver. The data information is encoded within the pulse duration. Furthermore, We conducted the study of the received pulse behaviour using Oscilloscope.

Pulse behaviour study in the receiver section: In our present study, we employ a diode laser source within the wavelength range of 630nm to 690nm for the transmission of textual data. This laser source is integrated with a feedback loop and a 4x4 keypad, facilitated by a microprocessor, specifically the Arduino NANO. The keypad serves as our input mechanism, allowing us to select the text to be transmitted. Subsequently, the selected information undergoes processing by the Arduino, where it is converted into binary pulses. These binary pulses are then directed towards an LED source for transmission purposes. The recipient side of our system utilizes a light-dependent resistor (LDR) along with a Arduino UNO microprocessor to decode the transmitted data. By manipulating the light pulses on the transmitter end, we can convey unique data patterns. The receiver instantaneously captures these pulses at the speed of light (approximately 3 x 10^8 meters per second) and proceeds with the data decoding process. validate the behavior of the pulses, we employed an oscilloscope (OWON Oscilloscope-FDS1102) to measure the voltage drop across the Light Dependent Resistor (LDR), as depicted in Figure 2. The figure illustrates our experimental setup, encompassing both the transmission and receiver sides. We interfaced a 16 x 2 LCD display with the microprocessor to show the decoded received data. In Figure 2(b), we observe the voltage drop across the LDR as a function of time following multiple presses of keypad key 1, recorded by the oscilloscope. Each keypress results in the generation of a single pulse, with a pulse duration of 32 milliseconds for the 1 key. Figure 2(c-d) presents the systematic pulse behavior for all the keys on the keypad. Subsequent analysis of the pulse widths allowed us to create a plot correlating pulse width time with keypad numbers, as shown in Figure 2(e). Notably, different keys exhibit distinct detected pulse widths, facilitating straightforward decoding. For instance, the maximum pulse width of 317 milliseconds corresponds to "keypad key D." Should the need arise to transmit multiple data streams synchronously, we would require an array of diode lasers on the transmission side and a corresponding array of LDRs on the receiver side.

Conclusion: Within this work, we introduce a straightforward yet effective Li-Fi model system for wireless data transmission via optical signals. Our approach harnesses the Pulse Width Modulation (PWM) technique to convey encoded data through pulse duration variations. To substantiate our claims and delve deeper into the behavior of pulse widths, we conducted a meticulous examination using a high-precision oscilloscope. This study enhances our understanding of the pulse duration dynamics and reinforces the validity of our proposed model. 

(This project was done by Sintu kr. Middya1, Surajit Paikara from Uluberia Govt. Polytechnic under my guidance)

Patient management during COVID-19 faces severe issues of lung damage, and the ventilators must be able to handle situations of rapidly changing lung compliance leading to potential collapse and consolidation. The driving pressure of the ventilator is the most crucial factor for patient outcomes particularly in case when a low tidal volume is being delivered. In light of the extreme importance of the pressure monitoring, our ventilator will accommodate three basic modes of control which further branch into seven individual modes in total. The basic three modes are Pressure Controlled mode, Volume Controlled mode and Spontaneous mode. The pressure controlled mode will include: PC-CMV (Continuous Mandatory Ventilation), PC-SIMV (Synchronised Intermittent Mandatory Ventilation). The volume controlled mode will include: PRVC (Pressure Regulated Volume Control), VC-CMV, VC-SIMV and lastly spontaneous mode will include: CPAP (Continuous Positive Airway Pressure), PSV (Pressure Support Ventilation) mode.