HOW TO: Send Audio/Your Voice Over a Beam of Light




Have you ever seen those music-synchronized lights before? They're pretty neat. This intructable will show you how to make a device that sends your voice or any other form of audio over a beam of light. The picture below is the finished product. I found the information on this project here. Please note that I used a lot of salvaged parts for this project; you could ultimately make a much better version with the right parts. I have tried to use this setup with a laser, but they seem to be too sensitive, and burn out easily. If there is a very simple solution to using a laser with this, please let me know. There are videos of it in action below.

Step 1: The Parts

You will need:

-A CdS Photocell
-Some battery holders with battery clips if needed (one for the audio-to-light modulator [transmitter], one for the receiver, and one for a microphone (optional))
-One microphone
-An Audio Output Transformer (RadioShack Catalog No. 273-1380)
-Some form of amplifier (I used a battery-powered one from RadioShack (Cat. No. 277-1008))
-Some MONO (NOT stereo) audio jacks (Three will do)
-Some form of LED, Preferably a bright one
-A container to hold all the doo-dads in (for the transmitter). I just used what I had: a pill container. You want to keep all the circuitry concealed in some form of container, because if you touch the circuitry, I found out it gives you a small unpleasant shock (because of the transformer?), and it disrupts the signal to the LED, therefore giving you a bad signal.
-Some hook-up wire

The Pictures below are what I had to buy (except for the mics). I salvaged the rest.

Step 2: The Schematics

These schematics were taken straight from the website I cited.

Step 3: Assembling the Transmitter

The assembled circuit should look something like this. Be sure not to bother with the black lead from the transformer; it is not used in this circuit. The cap of the pill bottle (to the right) has two holes drilled in it for the LED, which I just got from a solar patio light. Make all the connections with alligator clips FIRST to test it, then solder it all together when you know it works properly.

Step 4: The Receiver

The receiver is so simple, a monkey could do it. All you have to do is solder the CdS photocell in series with the battery pack (3 volts), and then solder the two resulting leads to another mono jack. Use the biggest photocell you can find. Also note that it does not matter which way you connect the photocell; it has not plus (anode) or minus (cathode) sides.

Step 5: The Microphone

The Microphone is also extremely easy to hook up. Connect it the same as you did with the receiver. You can find these microphones in cordless phones, answering machines, etc. The one I used came from a broken cordless phone. Once again, the batteries are just to give the microphone some power so that there will be some signal to the amplifier.

Step 6: Using It

To use it, just plug the transmitter into any audio source (CD player, radio, etc.), and turn it on! It will modulate the sound signals into light, and the receiver (plugged into an amp) will turn it back into sound! If you want to modulate your voice, plug the microphone into the input on an amp, and the transmitter to the output (to external speaker) jack. The final product may look a little like the below picture.



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    84 Discussions


    Question 1 year ago on Step 3

    Hi RPisces,

    I am doing a science fair project and am having a bit of a problem. I'd love some help! My problem is below.

    As you may know, Radio-shack is going out of business and the transformer is no longer in stock. I did however, manage to get a TL-013 Transformer but i'm not sure how to wire it. Could you help?


    2 years ago

    I don't think that LDR is well-suited on such speeds, its response time is too slow to have quality sound. I would recommend a photodiode, or for simplicity, a small solar panel found in most calculators, it will work even better.


    3 years ago

    Does the diode receive thing actually work? I'm going for he receiver here, cuz I'm doing he lazer window audio receiving thing, and I want a simple receiver, THAT WORKS!!!!

    Pyro Fiend

    7 years ago on Step 6

    This is SOOOOOOOO cool. I can't believe it's this simple and actually works!
    I didn't understand what it was at first, though; I thought this was an LED display that was in sync. with an audio input (like a visualizer, kind of). When I realized what it actually was however, it blew my mind. Very cool. Good job.


    9 years ago on Step 2

    Could you tell me the purpose of the transformer here? I mean, couldn't we just use the audio signal to go in the LED so that it blinks as signal amplitude goes up and down? Sorry, i'm a noob. My idea is to put a small microphone instead of a jack, that's why i'm asking.

    2 replies
    Pyro Fiendponsshin

    Reply 7 years ago on Introduction

    Transformers are very important here. Audio signals tend to be really low voltage (the audio output from my MP3 player doesn't even turn on a low voltage transistor). You really do need to step-up the signal in order to get it to work, also because the LED won't get a "clean" output without it.

    Magic Raisinetsponsshin

    Reply 9 years ago on Step 2

    The reason there is a transformer is because the voltage of the audio signal is not enough to really do anything at all, so the transformer is there to more or less boost the voltage of the audio.


    8 years ago on Step 2

    can we use an amplifier instead?

    Can't find an audio transformer here


    11 years ago on Introduction

    This seems pretty cool, but I have a hard time imagining what it might look like. If you ever get around to making a video of this I'd love to see it in action.

    5 replies

    Reply 11 years ago on Introduction

    Ok. I have posted two videos. One is just of some Pink Floyd being modulated into light. The other is with the microphone, and some Pink Floyd playing on my stereo, being picked up by the mic and turned into light. Enjoy!

    i tried this n it worked,but with a lot of noise though,as for the reciever i tried using a photovoltaic cell with o/p of 2v, n then connected it to a guitar there anything better i could do with the receiver maybe connecting a photvoltaic cell of 0.5 v or 1v...


    Reply 11 years ago on Introduction

    Thanks for the vids. It's really cool as-is, and it really gets you wondering about other possibilities as well. Brilliant.


    Reply 11 years ago on Introduction

    It should look like a laser pointer dot shining on the CdS cell, but I don't see a laser here. But that's OK, the LED will work for a demonstration.


    I am using a phototransitor and the receiver doesn't work. I don't know if it could be the laser. Is there any special laser that will work great with this project. On another topic: other than radioshack, is there any other good store to get my electrical components from even if it is a web store?

    1 reply

    Reply 9 years ago on Introduction

    well first of all a photoTRANSISTOR is completely different from a photoRESISTOR. Be sure to use the ladder in this circuit! And no offense to RadioShack, but if you don't want to spend so much money you short yourself a freaking HOUSE in the future, shop somewhere like or

    7Chris Crash

    9 years ago on Introduction

    I am working on this project for a science fair and I have made the circuit, but it fails to fluctuate the laser signal. I'm driving the circuit with a small radio receiver giving out about 2.4v and low amperage. Why isn't it working?

    1 reply

    Never mind. I found the problem, it was that my laser was non variable. It stayed at a constant brightness after a certain voltage.