Light To Sound Converter


[Alex] built what he calls a light to sound converter. It reacts differently depending on the type of light: remote controls, light bulbs, TV screens, etc. A photodiode is used with an amplifier to pick up the light change. That signal is dumped through a dual opamp. He swapped in several different types of photodiodes and settled on the BPW34 intended for visible light. He’ll be incorporating this into a much larger project.

21 thoughts on “Light To Sound Converter

  1. This could possibly be used to measure the wavelengths (frequency??) of different lights. Instead of having the output hooked up to a speaker, hook it up to an (ohm meter??) or something else that could make sense of the electrical pulses coming from the project.

    Then…find a way to record and reproduce the frequency, send it to an optical output, and see if it matches the original light input.

    If this could be done, and the wavelength (frequency?) could be changed to produce different light patterns or colors. Then your venturing into something that certain sectors of the government might be interested in.

    1. You’d need to do a lot of math to translate one from the other.
      Sound vibrates, in a general sense, much slower than light. But does overlap in the 100GHz to 10THz range. But am not even sure if those frequencies are audible to humans? Having forgotten the lower and higher ends of our range of hearing.
      So, You’d need to have a device which takes a light signal, and does some simple math to convert the frequency from the light into a representative slower audio frequency.
      Or, light gets made I to an inaudible sound which is recorded. Then, even though you won’t hear it, point the ultra or infra audio back to light, and yes, You’d get the same color. But, would only be audible if our range, which I remember now to be 20Hz to 20 KHz. So if you are talking genuine conversion, and not merely representation (like a figurative language: sound A = light 1, sound B = light 2 etc), then we would not be able to in any way at all hear those noises. But only see the light translations at either end of the process sound to light, then light back to sound. But, again, you won’t hear anything unless you happen to be a superhero. Which sadly, I found I was not.

      One application though, potentially, is to shine a decent Lazer onto a mirror which is on a speaker, sheet of glass, or otherwise vibrating surface. With the vibrations there deriving from noise in the room like talking, or music. Technically the mirror should vibrate at approximately same rate as the audio.
      So theoretically one could then translate rhe reflected light back into audible sound.
      But that’d now be James Bond territory with the resultant legal mess of eavesdropping! Lol

  2. Way back in 8th grade (I’m in college now), I did a science fair project on this called “Light Into Sound”. I made this circuit and did some experiments using different light sources, noting that our ears can hear faster than our eyes can see. I was the only one who didn’t take the easy way out and do some bean plant growing. It was a fun project, but I got a B for my grade while everyone else (who did plants) got an A, only because my teacher didn’t believe that I made the circuit myself.

  3. @Brownsy67

    Yea, they could shift infra-red into a sort of.. lovely green colour and call it… night vision.. or maybe even do it with thermal frequencies and call it.. thermal vision..

  4. @mcclanahoochie: [only because my teacher didn’t believe I made the circuit myself]

    People keep asking why I never went back and finished my degree after losing my scholarship because my GPA slipped to 3.49. This kind of crap had a lot to do with it.


  5. @mcclanahoochie

    I made a similar device back in Junior High (been awhile… I’m a PE now.) (It was a light wave communicator to be specific.) I entered a science fair, and got 3rd place. First place was some bean growing project. I later found out that I got 3rd instead of first because the judges weren’t sure if I had actually built the circuit.

  6. Fun project :)

    “This could possibly be used to measure the wavelengths (frequency??) of different lights” This would require very high-frequency sensing, while this is working with low-frequency variations like 50 Hz / 60 Hz mains hums and remote blinking.

    “our ears can hear faster than our eyes can see” I understand what you’re getting at, but I feel like it’s worth clarifying that this doesn’t mean our ears get more information. Our ears hear the amplitude of many different frequencies simultaneously every moment from two perspectives, while our eyes see only three frequencies but at many points (again, from two perspectives). Persistence of vision keeps us from perceiving high-frequency changes in light, but that’s just because our eyes are specialized in a different way than our ears.

  7. wow. look at all the people here who got bumped from an a for a science fair project because the judges deemed it impossible for a student to make a circuit like this, eventhough building the circuit is the simplest part of it. i’m glad i’m not alone in that situation!

    this is a very nice, basic circuit. glad to see it here.

  8. i cannot imagine what is so special about this circuit. it converts light intensity variation at the photo diode to current variation feeding into the speaker. it has nothing to do with the wavelength of the light! what is becoming of hackaday!? and all these people about not winning first plce in a science hoo! grow up for heavens sake!

  9. This circuit is experiment #12 in the Radio shack 2000 in 1 electronics kit.

    Glad to see that for 2009 we lowered the bar for hack a day submissions.

    Next up: A transistor is used to increase the power switching load of an IC!!! It’s a MIRACLE!!!!! What a Uber Haxor!

    F34r my 3|173 h4(k1n6 5k1||5!!!!0n3!

  10. There was a tv show called rough science in which they created something similar. They took a can and covered it with tin foil and reflected the sun off it to a photodiode a considerable distance away. If you talked into the can it vibrated the tin foil which in turn was picked up by the photodiode and transformed back into sound waves. It was a nice concept that seemed to have lots of possibilities.

  11. I believe I remember building this when I was about 10. I think it was in the Forest M. Mimms engineers mini-notebooks sold at Radio Squack. Still an interesting project, but surely not worthy of Hack a Day. :(

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