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.



    • Sew Tough Challenge

      Sew Tough Challenge
    • Stone Concrete and Cement Contest

      Stone Concrete and Cement Contest
    • Sensors Contest

      Sensors Contest

    118 Discussions


    3 years ago on Introduction

    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.


    4 years ago on Introduction

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


    9 years ago on Introduction

    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 !

    2 replies

    Reply 4 years ago on Introduction

    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!

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


    Reply 7 years ago on Step 3

    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!


    7 years ago on Introduction

    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?


    8 years ago on Introduction

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


    9 years ago on Introduction

    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.


    9 years ago on Step 1

    can u replace the audio trans. with something?


    9 years ago on Introduction

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


    10 years ago on Step 3

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


    10 years ago on Introduction

    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

    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.