Music is stored on my mp3 player as magnetic patterns that are converted into vibrations of electrical current.   In my headphone coils, these vibrations, in turn, create a vibrating magnetic field.  Since there is a permanent magnet inside the coil, the magnetic interaction causes a physical movement creating sound waves (vibrating air).
I thought I'd add another step to this beautiful process by sending the electrical output of my mp3 player to a laser pointer and having the headphones pick up the signal via a light dependent resistor.  "Why?" you may ask.  "What is the practical implication?"  "Why not?" I say, and "none as far as I can see."  On the other hand, it is very cool to see (and hear) it work.

Step 1: Supplies

Here's what you'll need to recreate what I did:
* 1 cheap laser pointer
* 2 AA batteries
* 1 9V battery
* 1 battery holder for the AA batteries
* 1 battery holder for the 9V battery
* a few pieces of stiff insulated wire, each a few inches long
* 1 pair of cheap headphones
* 1 source of music, like an mp3 player
* 1 standard light dependent resistor (the small kind)
* 1 cheap electrical switch
* 1 soldering iron
* a bit of solder and aluminum foil
* some tape.
<p>does it work with video signal?</p>
Hmmm. I don't know. Never tried it. In principle, it should work with any signal. Let me know if you try.
<p>Hello Dear gwarbeh</p><p>i just tried but it doesn't work - I'm not sure but i think the transmitter work properly but the receiver has a problem - is there many differences between Audio and Video? </p><p>What is your idea?</p>
<p>This could replace the tin cans and piece of string we used to use as kids to talk to our friends in the house across the street :-)</p>
This seems ok i guess. Seen much better
Hi, It's a great idea.<br> <br> I will try to assemble this! I agree with the previous commentaries. It would be useful to amplify both the transmitted signal (so you don't drain too much power form the mp3 player) and the received signal (improving the signal to noise ratio).<br> <br> You also should consider the components &quot;<a href="http://en.wikipedia.org/wiki/Frequency_response" rel="nofollow">frequency response</a>&quot;. Depending on the component characteristics, the signal level can drop significantly on high frequencies.<br> <br> Thinking about the ampops, you can use the ones specific for audio. They work in the proper frequency spectrum.
cool idea! I think rimar2000 is right about non-linearity, another thing I would suggest is to amplify the audio signal with an op amp (to improve signal to noise) and to use a capacitor to hook the incoming signal up to the battery. Check out the way i amplified and biased a microphone signal in <a href="http://www.instructables.com/id/Arduino-Audio-Input/">this project</a>.
Thanks, amandaghassaei. I totally agree about the op-amp; I need to boost the signal for sure. I don't understand why I'd want a capacitor in the receiver circuit though. I don't think I need to bias the signal, as it's just passed to the earbuds. Maybe you meant as a sort-of simple lo-pass to filter out some hi-freq noise? <br>
I meant that you should amplify and bias the signal before you send it to the laser.
Oh. That makes more sense. Learning about how to do that now. Audio Laser 2.0 should be better. Thanks for the help.
Maybe the type of LED you are using have not so linear response as you need. Ask those who know, I am only guessing. <br> <br>Nice work!
Thanks, rimar2000. <br>Huh. I never even worried about the linearity of the laser. Maybe that is part of the problem. Gotta do some research there. <br> <br>I was thinking it was more in the LDR. Also, I think I need to throw an amplifier in the receiver circuit to get out more signal.

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