In Februrary of 1880, Alexander Graham Bell and his assistant Charles Sumner Tainter invented a device that allowed the transmission of sound via a beam of light. It was called the Photophone. Bell believed the Photophone was his most important invention! Indeed, 100 years later in the 1980s fiber optics came into widespread use. It is noted on a plaque that on June 3rd, 1880 the first wireless transmission of a telephone message using the Photophone took place. This year marks the 131st anniversary of this event.
Bell’s Photophone used crystalline selenium cells at the focal point of its parabolic receiver. My version uses a solar cell as the receiver. The transmitter is a mirror attached to a speaker aimed at the solar cell. The mirror is aligned so that it reflects the Suns rays onto the solar cell. The solar cell is mounted at one end of a black 4″ ABS pipe about 2 feet long. The light reflecting off the mirror is modulated by the vibrating speaker. The Solar cell receives this modulated wave of light and outputs a corresponding modulated voltage that can be fed into an amplifier and output through a speaker to produce audio. A 0.1 uF capacitor is connected in series between the solar panel and the amp.
The whole project is quite simple and fun to build. Enjoy the video and.. as always, Keep On Hackin!