Photophone: Design of an Optical Wireless Communication System

2019-01-22

EE313 Analog Electronics Laboratory

In my 3rd year in Bachelor’s, I designed an optical wireless communication system for Analog Electronics Laboratory. This is a modified version of Bell’s photophone using electrical modulation of transmitted light. The design only consists of analog electronic components.

Photo: Prototype circuit on a single piece of breadboard
Photo: Prototype circuit on a single piece of breadboard

The system gathers the surrounding sound via a microphone and applies Automatic Gain Control to ensure the audibility of any dominant sound. Then, it is summed with a constant reference signal (see: multiplexing). Then, a laser transmits the modified sound to a receiver, which is a photodiode. This signal is separated and converted back into the speech signal and reference signal (demultiplexing). Additionally, the system also features a volume controller, a clipping check, a signal level indicator, a speaker switch for the times when the signal is too poor, and a Class AB power amplifier.

Video: Presenting the inner workings of the project.

EE313 Project Video: Photophone

Figure: Block diagram of transmitter and receiver units
Figure: Block diagram of transmitter and receiver units
Figure: Modular circuit design for the project
Figure: Modular circuit design for the project