Help with laser microphone

Thread Starter

amsmbmdasan

Joined Feb 17, 2022
3
I am not an electronics person. Attempting something similar to a laser espionage microphone, but for a fun event. It is a very basic set up. Laser pointer pointed towards a mirror at Home. Playing music near the mirror. The reflected beam is picked up by a solar panel or LDR going into a recorder. I tried feeding that solar panel's output to a Marshal MS2 guitar amp, but it does not reproduce any sound - just get a buzzing noise. But when I connect it to a recorder (smartphone or computer) and record it, interestingly it is able to get my voice when I make a loud noise, but not the audio streaming or any regular noises around :).

All the DIY videos make this look so easy - Does this actually work? Sincere apologies if this is basic (I suspect it is) Any help would be appreciated.
 

KeithWalker

Joined Jul 10, 2017
2,358
A solar panel probably has a really bad frequency response. An LDR in a simple foil covered cardboard parabolic reflector would give much better results. It would be directional and would amplify the signal.
 

AnalogKid

Joined Aug 1, 2013
10,067
You will need a phototransistor or photodiode as the sensor. These are more sensitive and have a frequency response wide enough for audio. A search for

light beam communicator circuit

will get you lotsa schematics.

ak
 

drjohsmith

Joined Dec 13, 2021
404
You ask about why the signal into a computer is heard, yet into a guitar amplifier is not,

Could be a few things,
most likely is sensitivity / input impedance.
The guitar amplifier is probably expecting a very small signal,
where as the computer input is probably expecting a bigger signal, especially if it the line input,
 

Audioguru again

Joined Oct 21, 2019
4,712
You want the vibrating mirror to amplitude-modulate the laser beam. How? Maybe your light detector must be fairly far away so that the beam of light goes back and forth over the sensor.
When sounds vibrate a mirror, its rigidity limits the levels and frequencies that cause a vibration.

A solar panel is much too slow for audio. An LDR is also slow but might be activated with very low frequencies.
You need a photo-diode or photo-transistor plus a preamp for it.
 
Top