Converting Laser beam detected on photovoltaic cell to audio signal

Projects General Guidance
1

Hi All, I am taking a project for showcasing vulnerabilities of security and I wanted to see if its feasible to do it with arduino component. Below is my Project description

I want to retrieve human voice from a conversation happening inside a closed room, through the windows. I found a way to do it by passing laser light to the window which reflects back to a photo voltaic cell with the human voice pattern.

Now, I need to figure a way to connect photo voltaic cell to an audio device which results in the human voice. Can i attach arduino component to the photo voltaic cell and then have audio device at its output console? Any leads/guidance is appreciated. Thanks in advance

Regards,
Deepak

2

First decide how the human voice is encoded in the reflected laser light. Then you can build something to recover it.

Paul

3

Hi Paul,

Thanks for the revert.

Glass is a very good reflector of sound vibrations. So the sound waves which hits the window glass on the inside room also reflects to the outside. Laser light when focused on the window carries these sound patterns automatically and these vibrations are directly focused on the photo-voltaic cell. I hope I answered your query

Regards,
Deepak

4

No you didn't. Is the voice amplitude modulating the laser? Or is it frequency modulating the laser? Different devices will be needed to recover the voice. Are you projecting the laser at exactly 90 degrees to the glass or at an angle? when at an angle, the voice modulation will show phase differences over the entire returned laser light.

Also, if the glass is not perfectly smooth, the reflected laser light will contain minor phase differences which will be noise in your recovered audio.

Paul

5

This was done in the 1970s using purely analogue techniques, so I'm guessing that an Arduino is seriously underpowered.

6

Most people simply connect the photocell to the input of an audio amplifier with speaker.

Works surprisingly well.

7

jremington:
Most people simply connect the photocell to the input of an audio amplifier with speaker.

Works surprisingly well.

Then the laser return signal is amplitude modulated. I wonder how well it works with modern double pane glass?

Paul