Audio Using Light Modulation

Valentin, VE7ZFR, along with his friend Isaac, recently gave the club a demonstration of a light-based audio communication system that they built. Their project used light photons rather than radio waves to transmit sound, making for a creative and impressive example of alternative communications technology.

On the transmitting side, audio from a phone or other headphone-jack device was fed into an amplifier circuit. That circuit both amplified the signal and used it to vary the intensity of a powerful LED light source. In other words, the audio was used to modulate the brightness of the LEDs.

On the receiving side, a solar panel detected the changing light intensity and converted it back into a changing electrical signal. After filtering out the DC component, the remaining audio signal was amplified and sent to a speaker, where it could be heard clearly.

The system achieved a range of slightly more than 100 metres. To reach that distance, the builders used a 12V 8A battery, two LEDs, and a reflector lined with reflective film to direct as much light forward as possible. A reasonably large solar panel on the receive side was also important, since a larger panel captures more of the transmitted light.