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

Picture of 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.

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Step 1: The Parts

Picture of 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

Picture of The Schematics
These schematics were taken straight from the website I cited.
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Pyro Fiend3 years ago
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.
ponsshin5 years ago
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.
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.
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.
smukherjee13 years ago
can we use an amplifier instead?

Can't find an audio transformer here
whatgives7 years ago
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.
RPisces (author)  whatgives7 years ago
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...
RPisces (author)  fear_black_death5 years ago
You may need to construct a simple audio filter circuit.
Thanks for the vids. It's really cool as-is, and it really gets you wondering about other possibilities as well. Brilliant.
VIRON whatgives7 years ago
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?
RPisces (author)  Theinventor945 years ago
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
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?
Never mind. I found the problem, it was that my laser was non variable. It stayed at a constant brightness after a certain voltage.
navaburo6 years ago
To use a laser to send audio I recommend the schematic from my instructable
bananafred6 years ago
Please help. I got a $5 laser level from Radioshack. I took it apart, removed the lens, and I turned it on, and it was a nice bright dot. Then, I put the transformer in series, turned it on, and it became very dim. I had to up the voltage to 4.5 volts to make it a little bit brighter. I then returned it to the way it was originally and it is still dim. Did the transformer ruin the diode some how? I can't see how that could happen.
i have a notebook that can transfer IR can i use the notebook to transfer music through the IR led?? i have an ir reciever and some other stuffs. thanks in advance!
It may be hard to get the IR LED in your notebook to transmit analog audio signals, you would need to write some fancy software if it's even possible.
RPisces (author)  J50Nunlimited7 years ago
yes, you can transfer the music over IR-- but I think that IR has a shorter wavelength than visible light, so it may not go that far.
has longer wavelength
locofocos6 years ago
Nice. I built one and it works fine. I can't get more than a few feet away until it stops working, but it's still cool. I was going to hook up my laser to it, but then I realized my laser blinks really fast to save power and create a strobe effect when you move it around.
DrCoolSanta6 years ago
Nice, I had already seen this on the website... Anyways, I liked this one, just couldn't ever arrange for supplies. Btw, you could also use a solar cell.
Finnly6 years ago
I remember in school I did something like this. We were using lasers to talk far away using a microphone hooked into a laser and the light sensor was hooked into an amp. It was pretty cool talking across the room. Nice instructable.
kennyvs7 years ago
hey i love this project but im having trouble after connecting all the parts of the transmitter. When i add the power the light does turn on, but the light doesnt blink after i connect the mono jack into a source, it just on on but not blinking. I was wondering "do you know the problem?
the laser blinks too fast to be able to see, it might look a bit dimmer though.
Ed656 years ago
Interesting project but one thing I'm not clear on... How exactly is the microphone wired to the batteries? Could you include a diagram showing that? Couldn't the microphone just be plugged directly into the Radio Shack Mini-Amp? I've tried previously to build a similar version of this project w/o the audio amp but could never get it to work. Please understand that I'm not nit picking your project, I'm just trying to understand how to get it to work for me since previous my previous (similar) projects have been exercises in futility. Thanks!
RPisces (author)  Ed656 years ago
just wire it in series. Note that this microphone is a condenser, not an electret
How do wire it in a series
RPisces (author)  shaphieh6 years ago
Search Google for 'wired in series'. And actually, a correction to myself, it IS an electret; a condenser is, as I found out, a type of electret mic, but just has two leads. Sorry for the confusion.
NotAMember6 years ago
(removed by author or community request)
RPisces (author)  NotAMember6 years ago
Yes, you can use that, but the audio might not be very clear compared to the amp from radioshack, and I'm not sure if that circuit works; I haven't built it.
hydrnium.h26 years ago
Is the photocell really so sensitive it can detect minuscule changes in the laser's output?
selaja7 years ago
sorry. i am like a non-tech person. what does it do? i have never seen one before...
(removed by author or community request)
ok, thx
jonnxt7 years ago
you could also use the two pack IR diodes as well.
jonnxt7 years ago
try using a photo diode instead of an photo resitor.
hanker7 years ago
dude what watts is the audio transformer pls can you tell me
Hey its the only audio transformer RS carries. (yours might carry more, but mine only has one)
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