Introduction: Transfer Sound on a Laser

This is a neat project I picked up about a month ago. It's a simple project allowing you to transfer sound across a space on light with little quality loss. The credit of this project goes here

Step 1: Gather Your Materials

Things You Will Need:

Two Mono Jacks
1 Audio Transformer
1 Solar Resistor
1 Laser
1 Single AA Battery Clip (for reciever)
1 Triple AAA Battery Clip (for laser)
Batteries (1 AA, 3 AAA's)
Some wires and tape

A breadboard is optional, but I chose to use one to save time.

Step 2: Add a Mono Jack

Start by adding two wires to the leads of a mono jack. This will be the input of your transmitter.

Step 3: Add the Transformer

Next we add the first two wires of our audio transformer. Connect the red and white leads of the transformer to the mono jack.

Step 4: Connect the Other Leads

The blue and green leads need to be connected to the breadboard and will later be connected to the laser. The middle black lead will not lead to anything, so it's best to wrap a piece of electrical tape around it, as I have done.

Step 5: Complete the Transmitter

Next we add the laser. The green lead of the transformer connects to the negative lead of the laser, and the positive lead of the laser leads to the positive lead of the battery. If everything is connected properly, you should be able to turn your laser on. This is the completed transmitter.

Step 6: Using the Circuit

Now that the transmitter is built, you can use it. Simply connect an audio source (such as a CD player) to the mono jack and turn on the laser. The modulations of current produced by the audio device causes the laser to modulate accordingly. It will get slightly dimmer and brighter, depending on the music. However, this is very difficult to detect by the human eye, and it isn't particularly useful. In order to make the circuit useful, we need build a reciever.

Step 7: Building the Reciever and Using the Device

The reciever is the easiest part. Connect your second mono jack to the solar resistor and battery. You can even place it on the same breadboard, as I have. Just make sure you keep the circuits seperate.

As stated before, connect an audio source to the first mono jack (the one connected to the laser) and turn the laser on. Connect the other jack to a reciever (such as an amp or the mic. port of your computer) and aim the laser at the solar resistor. The light modulation of the laser are reversed on the reciever and converted back into sound.

Step 8: Alternate Construction and Theory

Instead of using a battery and solar resistor, you could just use a small solar panel. However, these are more expensive and tend to break more easily.

Theory: It may be possible to bounce the laser of glass behind which a conversation is occuring (such as a window) and pick up the sounds on the reciever, but I've yet to test it. Please let me know if anyone has tried this or has a better way to do this.


MrMxylptlyk made it!(author)2015-09-16

Hello m8, I got some LM386 amps (IC ship, very cheap on eaby if anyone interested), I am wondering if i can use those instead of the physical transformer amplifiers. I mean the basic goal of amplifying signals is achieved. It would reduce the size of my project and would be cheaper. Thanks.

Ivelyn19 made it!(author)2014-12-30

Where can I find audio amplifiers?? where can it find it most?

kamathln made it!(author)2009-10-08

Oh Boy! This reminds me of a funny happening. When in college, my classmate had done this very project at home. One early morning he brought it to the college's electronics lab to show off.

The electronics lab is soundproof, so we should not actually hear the morning prayer which is loudly sung using a loudspeaker. But on that day, we did hear it faintly! We guessed the door was not completely closed. Anyways, with respect for the prayer, we all stood up. After a while our ears were able to finally locate the sound and realize the door was closed after all. The prayers were coming from the reciever!

What actually happened completely stunned us! The college used a loudspeaker/amplifier which induced the signals strongly back into the lighting power supply. It was a cloudy day, and we had switched on the lights in the electronics lab. So we got the "signal" that was being "transmitted" by the speaker/amplifier !

ross33 made it!(author)2011-07-26

thats pretty funny how clear was the sound?

kamathln made it!(author)2014-11-20

It sounded a slightly muffled .. but clearer than how it would sound if the glass door was justa bit open.

Oh boy .. this must be the slowest conversation ever .. 2006 article - 2009 comment . 2011 reply and 2014 re-reply!

frogjake9 made it!(author)2010-05-20

I can't seem to find a solar resistor anywhere. Where can I get one?

sarvesh7 made it!(author)2014-04-27

if u cant find cds then find ldr . both are same

Antzy+Carmasaic made it!(author)2010-08-17

you can search for LDR(light dependent resistor)... i think....

ElectroPro9460 made it!(author)2012-06-17

where can i get AUDIO TRANSFORMER at home?what are the appliances using audio transformers?

RAYED made it!(author)2010-10-30


ElectroFlex made it!(author)2012-05-18

I began this project a while ago (have yet to finish) and I found one at Radio Shack for around $2.70. The catalog number is 273-1380. Good Luck!

pratikreddy made it!(author)2012-04-14

I tried this experiment. Everytime I tried, my laser is weakening and losing strength. Sound is not trasmitting. If I connect directly to speakers from Audio and battery it's working. I lost few lasers so far $15 energizer and couple of regular lasers. Can you please help?

ZenX made it!(author)2011-01-12

instead of using a single laser, could this function with many LED's?

rejsps made it!(author)2010-04-14

I built a laser pointer modulator many years ago using a power FET instead of a transformer.  I biased the gate using a voltage divider with one leg being a potentiometer.  The audio was coupled in through a capacitor (0.22 microF).  With no signal, the bias was set to have the laser partially on.   Then the audio modulation was in a fairly linear part of the laser diode's I-V characteristic.  The resulting audio is very high fidelity when picked up by a good photodiode.  FYI, the power FET came from Radio Shack, but they no longer carry it.

jules15 made it!(author)2010-03-29

can u replace the audio trans. with something?

akinich made it!(author)2010-01-18

hey nice instructable
is it possible to get the audio transfrmer out of any items then just buying
i kinda the recycling type

Theinventor94 made it!(author)2009-06-14

If I connect the transformer with the lower ohm side being the laser side, what differences would it make?

Theinventor94 made it!(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?

saites2001 made it!(author)2009-06-09

Without knowing more specific details about your problem, I would venture to guess that it's not the laser. Any general purpose laser should do. I find it more likely that you don't have something hooked up correctly. As far as an electronics store, online is probably your best bet. I like Jameco, but Digikey is also a good and popular supply company.

Theinventor94 made it!(author)2009-06-08

What laser did you use?

bing2you made it!(author)2009-04-09

I, like ReCreate, would also like to know what model of transformer you are using. I'm a beginner, maybe it isn't very important, but I thought I'd ask anyway.

7Chris+Crash made it!(author)2009-05-21

He is using a RadioShack Catalog No. 273-1380.

kyles89 made it!(author)2009-02-14

you can use phono jack to, just do it the same way have both channels going to the same place, and then ground to ground still. id use the phono jack cause sometimes the mono ones do not get all of the such as in fat bottom girls by queen, also with the phono one you could technically have the sound go to different places at the same time, for a different experience.

ReCreate made it!(author)2009-02-09

what kind of transformer is this? from how many volts to what?

aesopiankitty made it!(author)2008-12-20

Quick stupid question. I got the mono jacks, and I don't know how to wire them. Any help would be greatly appreciated. Thanks TAK

saites2001 made it!(author)2008-12-20

There should be only two leads on the jack. Connect a wire to each one of these leads. Next, add the mono jack to the breadboard according to the instructions and pictures above. Hope this helps.

aesopiankitty made it!(author)2008-12-21

i don't think my jacks have leads. did i screw up?

saites2001 made it!(author)2008-12-21

No. The jack should have a couple of places to solder wires to. In a sense, one of these is positive and one is negative. You'll be connecting these to one side of the transformer. It's been a while since I've done this project, but IIRC, it doesn't matter to which you connect each wire (of course, they can't be connected to the same lead). If you still are having problems, post a picture of the jack and we'll see if we can get this taken care of.

aesopiankitty made it!(author)2008-12-22

I think I see one lead. It's inside the jack, and when i shined a light into the jack, I saw it glimmer. Where do I put the other one?

saites2001 made it!(author)2008-12-22

I'm confused. You shouldn't have to shine a light into anything. Please post a picture so I can see what you're seeing.

aesopiankitty made it!(author)2008-12-24

hope this is helpful. where do i find the leads?

Photo 1.jpg
saites2001 made it!(author)2008-12-24

It looks like it has a covering on it. If I'm right, you'll have to remove that first. I was actually kind of expecting a picture from the side. Where did you get this jack? Did you buy it or harvest it?

aesopiankitty made it!(author)2008-12-26

I bought it from some store online. I'll look for the covering. What's it look like? Sorry about this and thanks for all your help.

saites2001 made it!(author)2008-12-26

On the jacks used in the project there is a sort of covering that screws over the jacks. The top of the jack is still exposed (to be inserted into a device), while the bottom (where the wires have been soldered on) are covered (to prevent electric shock). There is likely some sort of cover obstructing your view. There should be two distinct and obvious places on the jack itself to which you may attach wires (if it were a stereo jack, there would be three contact points). You don't have to apologize -- this is what Instructables was made for.

aesopiankitty made it!(author)2009-01-13

well after a long break i found them. thank you so much for all your help and one more question :P there are two leads: one in the center of the cavity of the bottom of the jack. and the others on the wall. which is positive and negative.

saites2001 made it!(author)2009-01-13

If I'm not wrong, it shouldn't make a difference. And if I am wrong, you can probably just reverse the wiring (as in no harm to the project). Sorry that I can't be more specific or directive than this.

aesopiankitty made it!(author)2009-01-14

believe me, after all that i'm more likely to kiss the ground you walk on than to be sad about specifics. i'll let you know how this turns out. thanks so much AK

wee_man made it!(author)2008-10-18

for this what types of diaodes is it leds red one or proper lasers or could i substitute the leds or ir leds and with add a lot of them and have a range of like 1km or so would this would be possible gradly apprishate some info please.

Alvin+Pontejos made it!(author)2008-08-01

what kind of laser you used for it? a laser diode? and can i ask for the circuit design please...thank you,

rrrmanion made it!(author)2008-07-27

could you forget the receiver and use it to control stage/party lights? e.g. control 4 lights with a 4 channel (quadraphonic) sound system and add a dmx output?

saites2001 made it!(author)2008-07-27

It sounds like it would work, but I'm not sure about the power requirements.

tdhelder made it!(author)2008-07-27

Concerning the wireless Ethernet, rather then switching the laser on and off why not bias the laser on and then just bump the voltage to change the intensity. The lag should be greatly reduced then. Effectively AM.

saites2001 made it!(author)2008-07-27

Well, though that may or may not be true (to be honest, I'm not exactly sure), I still wouldn't try it. Interference would be to great, and electromagnet waves (radio waves in this case) also move at the speed of light (light is electromagnetic energy). Therefore, wireless communication via radio waves just makes more sense. Using a laser would not theoretically be any faster, and would be more prone to interference and other issues.

Rocket+Boy made it!(author)2008-07-20

do you have to use mono jacks? couldn't you use decapitated earphone cords?

rrrmanion made it!(author)2008-07-27

yer if the earphones are mono you probably could

zachninme made it!(author)2006-10-14

Hey, do you guys think there is any way of doing this for a "wireless" network? The only problem I see, is that an eathernet cable has what, 8 pins? And that could get annoying. And if it goes through mirrrors or something, the 3x3 dot matrix (hypothetically) would be distorted. Then again, a wireless router has one output, the antenna. Maybe you could rig that up... or maybe not... Then again again, you could do a USB network, since that is really only 2 I/O's...

Zlwilly made it!(author)2008-05-06

I actually talked to one of my college professors about this awhile back. CAT-5 would require I think 4 lasers to generate the proper number of data lines. I wanted to set up a laser network that was controlled via a pair of microcontrollers, that way a wireless connection could be made between my house and barn.

The one thing that came to mind was whether or not you could turn the lasers on and off fast enough to generate the steady 'square wave' signals that CAT-5 is known for. And then I found this.

Hmm... Collaboration maybe? :]

mikemmcmeans made it!(author)2008-01-12

do it im going to try this with my wifi antennas cause my garage is too far away for my internet radio also try it with the audio i/o on 2 computers for linked conversation also also try it with coaxial input on a tv

Mr.Devious made it!(author)2006-12-31

You would need a laser for each pin on the ethernet cable, and a receiving counterpart aswell for each. Thusly, it would cost more than just using it for audio and is exactly why fiberoptic systems are still very expensive.

zachninme made it!(author)2006-12-31

Thats what I said ;-\

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