A bi-directional Li-Fi (light fidelity) optical communication system has been developed for high-speed, two-way digital data transfer over free-space optical links. Using laser diodes, photodiodes, and on-off keying (OOK) modulation, each module can operate dynamically as both a transmitter and a receiver, unlike the earlier unidirectional design published in June issue of EFY. This enables reliable bi-directional communication over the same optical link at data rates of up to 520kbps.

The system uses dedicated transmitter and receiver circuits with switching logic, together with handshake, packet-based communication, and checksum-based error detection to ensure reliable transfer of files of any type. It demonstrates the practical implementation of full-duplex optical wireless communication using low-cost discrete components and USB-to-TTL converters, making it suitable for academic study, system development, and rapid prototyping as an alternative to conventional RF communication. Fig. 1 shows the author’s breadboard prototype. Two identical system units were built and tested.

Fig. 1:



Author’s prototype

Circuit and working

Fig. 2 shows the circuit diagram of the Li-Fi transceiver module for bi-directional optical communication. It consists of two identical transceiver units, each capable of functioning as both a transmitter and a receiver. Each unit is built around a CH9102 USB-to-TTL converter (U1), an LM393 dual comparator (IC1), a BC547 transistor (T1), a laser diode (LD1), and a BPW34 photodiode (D1). Of the two comparators in the LM393, only IC1B is used, while IC1A remains unused.
- Advertisement -

Fig. 2: Circuit diagram of the Li-Fi transceiver module

On the transmitter side, the TXD (pin 6) output of the CH9102 drives transistor T1, which switches the laser diode on and off according to the serial data, thereby implementing on-off keying (OOK) modulation. The optical pulses are transmitted through free space to the receiving unit.

In the receiver se

📌 Bi-Directional Li-Fi Optical Communication System (India)
🏢 Electronics For You
📍 India