College of Engineering Poster Presentations

Document Type

Student Presentation

Presentation Date


Faculty Sponsor

Hao Chen


A visible light emitting diode (LED) is used to transmit audio signals from an audio source (radio) through a transmitter circuit to a receiver circuit. The constructed system demonstrates optical audio transmission. The purpose for this demonstration is to show how audio signals can be transmitted through a free space optical link using an illuminating LED. All signals being transmitted are analog. The transmitter circuit is excited with an audio signal that is level shifted and output using a visible light LED. In the receiver circuit located at some distance from the transmitter, a photo-diode sensor detects the light from the illuminating LED, whose signal is then reconstructed and amplified using an LM386 audio amplifier. The reconstructed signal is then output through a speaker to near or exactly as the original input audio signal. The system is designed to operate within 4 KHz-20 KHz frequencies that are high for the human eye to observe the flickering of the LED. The flickering of the LED is the mechanism through which the photo-diode is detecting the LED light transmitting the signal. Both circuit designs contain resistors and capacitors that contribute to the protection components and filtering of the analog signals.