Teacher uses cheap laser and solar panel to transmit wireless sound — iPad powers home project that was inspired by solar panel making noise when attached to speaker

Phil, a high school chemistry teacher and YouTube creator, noticed that a small solar panel emitted a faint sound when connected to a speaker and exposed to light. From this, he deduced that he could transmit sound wirelessly using light, with the solar panel acting as a receiver. So, he decided to build a wireless transmitter using his iPad, a solar panel, and a cheap speaker, and shared the short build on his YouTube channel.

The first thing he did was to build an amplifier to strengthen the audio signal from his iPad, and then attach it to an LED light, both of which are powered by 9-volt batteries. The light would then vary its intensity when pressing play, indicating that the LED is receiving data pulses from the iPad as voltage variations. He then checked the voltage output of the amplifier, and, indeed, it synchronized with the music.

Phil tested his solar panel and speaker combo by placing it near the light, and it played the music from his iPad. The only downside is that if he moved the contraption just a few inches away from the bulb, the sound strength drops off proportionally to the inverse square law, which says that light intensity decreases by the square of the distance from the source.

To solve this, he replaced the LED with a cheap red laser diode that concentrated the light in a smaller area. He then pointed it a few feet away across his living room, and when he placed the tiny solar panel and speaker combo along the path of the laser, it started playing the music quite audibly. Sure, it might not be Hi-Fi quality with crisp sound, but it’s good enough that you’d understand the words of the song.

This isn’t actually groundbreaking technology, and the military has been using lasers to communicate wirelessly over long distances since the 1970s. It eventually entered civilian use in the 2000s, helping to establish high-speed communications in areas where laying fiber optic cables is impractical. It does have its limitations, though, especially since laser communications require a clear line of sight for them to work.

Still, Phil’s cheap and easy recreation of this technology showed how accessible it has become to nearly everyone. Moreover, his videos may spark the interest of students, helping to inspire the next generation of engineers and inventors.

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