Bi-Directional Li-Fi Optical Communication System

The Bi-Directional Li-Fi Optical Communication System facilitates free-space optical data transmission using light as the carrier medium. At the heart of the transmitter stage is a CH9102 USB-to-TTL converter, which bridges serial data from a host computer running custom Python code. This digital signal drives a BC547 NPN transistor configured as a switching amplifier to modulate the optical output of a laser diode (LD1). As the transistor switches rapidly based on the serial stream, the laser diode emits pulses of light corresponding to the data bits. On the receiving side, a BPW34 pin photodiode acts as the optical sensor, converting the incoming light intensity fluctuations into tiny electrical current variations. This weak signal is fed into an LM393 dual comparator integrated circuit. The comparator references the incoming analog signal against a threshold voltage adjusted by a potentiometer (VR1), cleaning up the waveform and converting the optical pulses back into crisp digital square-wave TTL signals. These recovered TTL signals are then routed back through the USB-to-TTL converter to the receiving computer, completing a full-duplex communication loop supported by various passive resistors and capacitors that ensure circuit biasing, signal conditioning, and power stability.