Introduction: 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.

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.

Step 3: Assembling the Transmitter

Picture of 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

Picture of 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

Picture of 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

Picture of 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.


JohnL373 (author)2016-06-11

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.

bob8898 (author)2016-03-28

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!!!!

MaricarA (author)2015-09-16

Where are the videos? :) please :) thank you

Pyro Fiend (author)2011-05-25

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.

ponsshin (author)2009-08-01

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.

Pyro Fiend (author)ponsshin2011-05-25

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 Raisinets (author)ponsshin2010-01-21

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.

smukherjee1 (author)2011-04-19

can we use an amplifier instead?

Can't find an audio transformer here

whatgives (author)2007-06-12

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)whatgives2007-06-12

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!

fear_black_death (author)RPisces2009-09-22

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_death2009-09-22

You may need to construct a simple audio filter circuit.

whatgives (author)RPisces2007-06-12

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

VIRON (author)whatgives2007-06-12

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.

Theinventor94 (author)2009-06-09

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)Theinventor942009-06-09

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 (author)2009-05-30

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.

navaburo (author)2009-01-06

To use a laser to send audio I recommend the schematic from my instructable

bananafred (author)2008-12-24

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.

J50Nunlimited (author)2007-09-20

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!

bananafred (author)J50Nunlimited2008-12-23

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)J50Nunlimited2007-09-26

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.

jeymeowmix (author)RPisces2008-12-12

has longer wavelength

locofocos (author)2008-11-12

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.

DrCoolSanta (author)2008-08-24

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.

Finnly (author)2008-07-31

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.

kennyvs (author)2007-10-20

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?

corksean14 (author)kennyvs2008-07-16

the laser blinks too fast to be able to see, it might look a bit dimmer though.

Ed65 (author)2008-05-11

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)Ed652008-05-11

just wire it in series. Note that this microphone is a condenser, not an electret

shaphieh (author)RPisces2008-05-13

How do wire it in a series

RPisces (author)shaphieh2008-07-08

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.

RPisces (author)2008-04-30

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.h2 (author)2008-04-18

Is the photocell really so sensitive it can detect minuscule changes in the laser's output?

selaja (author)2008-04-18

ok, thx

jonnxt (author)2008-03-19

you could also use the two pack IR diodes as well.

jonnxt (author)2008-03-19

try using a photo diode instead of an photo resitor.

hanker (author)2007-12-10

dude what watts is the audio transformer pls can you tell me

thatswhatshesaid (author)hanker2008-03-18

Hey its the only audio transformer RS carries. (yours might carry more, but mine only has one)

RPisces (author)hanker2007-12-10

I'm not sure. You can look up all the information on it on RadioShack's website. Just search "audio transformer", and it'll come up.

numanumafan (author)2008-03-05

this project is so pimp. my friend did this for a school project. i think this revealutionized the way of listaning to music.

selaja (author)2008-01-02

sorry. i am like a non-tech person. what does it do? i have never seen one before...

Aerospaced (author)2007-11-08

Most of these projects use a transformer on the laser side. The laser diode is connected to one side of an audio transformer and then to the battery. The other coil is then connected to the audio source with a headphone jack. This will cause a change in the modulation in the beam that can be detected with your reciever. However, the laser is constantly on and subject to burn out. A OPamp is a small IC that can be put in place of the laser in the aformentioned scheme. You then take the output from this and feed it into a FET. FET's can switch on VERY fast and handle the current load. So, the OP amp will amplify the signal output by the transformer and trigger the FET wich will turn the laser on and of very quickly. This way when there isn't a sound being made the laser isn't on wasting energy and burning time. Check Digi key for FETS and OPamps

RPisces (author)Aerospaced2007-12-06

Oh. Duh. I just realized something (after I posted before, of course). Could I just use an LM386 Op-amp? That part is easy. But what kind of FET should I use? Aren't there all different package (case) types with varying amount of leads?

Aerospaced (author)RPisces2007-12-07

I would try a 7002 through hole type. They have 3 leads and are very simple to figure out.

RPisces (author)Aerospaced2007-12-06

great point! I have tried relentlessly to do this with a laser, but 1) my nice, expensive green laser pointer won't let me (must be the regulation circuitry), and then I bought a regular, el cheapo laser, but then found out that it was >1mw, and not >5mw. In other words, it was RIDICULOUSLY dim. I would love to someday create a 'professional'-grade communication device with this setup, along with all the wide-angle optics, tripods, high-powered lasers, and advanced circuitry, but that's up there in price. It's really cool to see some of the ones others have made and posted on the net.

Aerospaced (author)2007-11-04

Have you tried to trigger the LASER using an OP amp and FET? That should get the power to drive one at a rate that would allow analog sound transmission without underdriving the LED and causing burn out.

RPisces (author)Aerospaced2007-11-08


Detron (author)2007-09-30

I am having trouble wiring this i thought i had it but the led is really dim im not sure if i have the right photo cell or what im doing wrong any ideas please let me know thanks Deton

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