The book I have here is "Listen to Radio Energy Light and Sound" by Calvin R. Graf.
On page 127 he describes THE SOLAR CELL AS A MICROPHONE.
He writes "When the selenium solar cell is connected to an audio amplifier it will act as a microphone when you speak with your lips near the selenium surface layer."
Does that mean that our roof, assuming solar panels are installed, can become a listening device?
As far as I know the electric current through selenium is only varied by exposure to light, not sound waves. I believe Bell used selenium crystals in an early microphone but i don't remember the details.
At first I thought you were going to refer to modulated light sound, as is used in the optical soundtrack of movie film. If you look at a strip of 16mm sound movie film, you'll see the image frames, and along side them a squiggly band of sound waves. This is recorded when the film is shot by modulating a light beam to expose the film, and upon projection the projector has a little light beam that projects into this audio image and shines it into a photocell, the output of which is modulated current, sent to the amplifier. A system that worked so much more noise free than recording tape that Mercury Records had an entire division in the 50's and 60's that mastered Lp records from recording optically on film rather than magnetically on tape!
I can't imagine selenium working as a source for anything other than modulated light, not wound pressure. But I could be lacking some information here.
Tim in Bovey
Or, the dreaded "Green Fog" could possibly cause fluctuating light waves to collect on a cell and make sounds. Who knows..
My Neighbors/Friends already think that I'm nuts so I ain't gonna go out there, climb 20' feet in the air, and talk into my panels to find out.. 😉
Chapter 7 of this book is totally dedicated to using solar cells for "listening to light," so Tim is on target by mentioning optical sound.
Other uses of solar cells include light meter, observe electric lights glowing, listen to burning objects, listen to lightning, remote measurement using light, the solar cell as earphone, listen to auto headlights, listen to daylight, listen to the moon and others.
Well, I dug out the little photo voltaic cell I used in a high school Physics demonstration some 45 years ago. I modulated the light beam of a flashlight and used the photo cell connected to an audio amplifier to demodulate the light beam.
Sent music 25 feet over a light beam! Cool!
So, I just connected the photo cell to my mixer input. Shielding it from the room lights which are modulated with 60 Hz I yelled at the photo cell. My mouth right at the cell.
No sound. I even tried tapping on the cell. No sound.
Must be some crucial info about that experiment we need to duplicate the results. In the meantime, maybe this could be adapted for use as an STL. Now, where's that flashlight...
I don't spot any crucial information that jump-starts using a selenium solar cell as a microphone... The opening of Chapter 7 gives a several-page theory and background of photoelectric or solar cells, noting there are two types of these photo-voltaic cells: selenium and silicon, as was mentioned by Neil Radio8Z at last night's ALPB meeting.
I'll quote the microphone section in its entirety:
THE SOLAR CELL AS A MICROPHONE
The selenium solar cell is a rather versatile device, doing a number of things extremely well, other things as well as accepted devices, and some things for which it does need improvement. When it is connected to an audio amplifier, the solar cell will act as a microphone when you speak with your lips near the selenium surface layer. The audio output is low and you must turn up the audio gain much higher than for a standard microphone.
The fidelity of the solar cell as a microphone is acceptable though it is not as good as that of a dynamic microphone. Microphonics due to solar cell vibration appears to be the method of operation since it works well in total darkness. Fig 7-17 shows the solar cell as a microphone. Experimentation with improved matching to the amplifier input, an improved means of mounting the solar cell to a case so it will be more responsive to vibration, and possibly other approaches may make the solar cell microphone a useful yet novel device.
Fg. 7-17 shows sound waves radiating toward the surface of a solar cell which is connected by its wires to an amplifier-speaker.
The concluding line of the chapter is interesting:
The author's observations have been confined mainly to noting effects in the audio-frequency range. There may be additional effects in other domains which are yet to be explored.