Instructables

Send Music over a Laser Beam

WARNING: this project involves the use and modification of laser devices. While the lasers I suggest using (store-bought red pointers) are relatively safe to handle, NEVER LOOK DIRECTLY INTO A LASER BEAM, BEWARE OF REFLECTIONS, and be EXTREMELY CAREFUL when MODIFYING a laser product. Also, I am not liable for anything stupid you do.

Here is yet another thing to do with those promotional laser pointers: send music (or data) from point A to point B over the laser beam using amplitude modulation. All it takes is pointing the moded laser at a detector, and music can be heard from an attached amplifier. The range and quality (or data speed) can vary, but I have gotten a HALF MILE of range with excellent audio quality and around 300bps of throughput.

The image shown here is the transmitter and receiver working across my desk during a test.

TO SEE HOW TO USE TWO LASERS TO TRANSMIT TWO MUSIC CHANNELS AND MIX THEM WITH A PAIR OF SUNGLASSES, check out the blog post here.

A video of the system working can be found here: http://video.google.com/videoplay?docid=6895048767032879458&hl=en

Much inspiration for this project came from http://sci-toys.com/scitoys/scitoys/light/light.html#laser_communicator
 
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Step 1: Gather Materials

Picture of Gather Materials
To send music over a laser beam you will need the following parts, most of which can be gotten for less than 5 dollars at radioshack total (besides the pointer, which probably costs $15). If you are on a tight budget, try replacing the laser with a red LED and a 100ohm resistor attached in series.

for the transmitter:
a laser pointer
batteries (D-cell work best)
potentiometer (variable resistor) 50k ohm or less
audio source (iPod, cd player, mic preamp, PC line-out, etc.)
some wire (cat5 aka ethernet cabling works best)
toggle switch (a turbo switch from an old PC works well)
audio transformer (can be pulled from audio equipment)
1/8" audio jack (can be gotten from the end of a headphones cable)

for the reciever:
phototransitor (photodiodes or IR detectors also work)
1/8" audio jack
some more wire
high-gain amplifier (laptop with mic input, or mic preamp plus amplifier)
magnifying glass (helps at great distances)

tools:
wire cutter/stripper
soldering iron and electronics solder
tape (clear and/or electrical)
digital multimeter (can be useful... not realy required)
tripod (helps for aiming laser at a distance)
empty pizza boxes with white backs (for finding beam and for adjustments)
some assistants
rdev44 months ago
how to make a laser cutting gun
Clarisse1 year ago
Why do i need audio transformer (i mean, how it works and what is the point of it) and where can i buy/find one (pls paste a link if you know a store or if you found it on ebay) tnx ahead, please reply quickly ;)
navaburo (author)  Clarisse1 year ago
Why? Because it allows the input audio signal to modulate the laser power supply while also electrically isolating the two circuits. -- Basically, it transfers the signal from the stereo to the laser magnetically, without actually making an electrical connection between the circuits.

This one featured at the link here will probably work: 
http://www.mouser.com/ProductDetail/Xicon/42TU120-RC/?qs=sGAEpiMZZMv0IfuNuy2LUU2nVj3GMLUawQykJuAOLGA%3d
hesh1231 year ago
Can you please tel me the Voltage & Current values required for the Audio Tramsformer ????
And Link OR a Site to buy a suitable Audio Transformer???
Hope quickly response as soon as possible....
please reply immediately!!!!!!
Ok, so my projects very similair only it doesn't work. I think my problems with the wiring and I don't know how to fix it.

I've got the laser wired up to the batteries and that turns on. If I test for sound now (even though no sound is hooked up) I'll hear a click noise every time I turnt the laser on and off.

Now when I wire everything up with the transformer all I can get to come out is the click. No other audio.

For the reciever I'm using a .5v 6watt solar cell.

If anyone could help I'd be thankful. I can also upload pictures of the project if that would help.
navaburo (author)  youngdemetre1 year ago
Your problem might be the photocell. I recommend trying a photodiode or phototransistor, because the photodiode is more sensitive than the photocell.

Another way to think about it is that the the photo cell is 8 W but your laser is in the milliwatts so it's your laser is way less than one watt to the signal from the laser is going to be very weak in comparison to the total signal from the photocell

Sorry if this comment doesn't make any sense I'm typing it with Siri
Ok, I think I understand, so the voltages don't matter for this case? I know the laser is being ran on 4.5 volts and the photocell is only .5 volts. I got the idea to use a photocell from kipkay (youtube for makemagazine).

I'm really thinking that my problem is the wiring on the audio transformer.
I just looked at the package again and it says that the power output is .5w and typical output voltage is 6v so I think the front of the package had the numbers mixed up.
navaburo (author)  youngdemetre1 year ago
Your transformer wiring could be an issue. Try changing it, and check the schematics from me or some other posters. You can also use headphones on the output to see if it's working. By this I mean you can hook up headphones directly to the transformer output pins with the laser and battery disconnected.

Cheers,
Chris
Thanks I just did that and the transformers working. I went from there and hooked the batteries back up and the laser and I vaintly heard the music! Then the batteries died =( I'll hook it back up once they're charged and thanks for your help! It's always the little things we overlook.
Edit: I tried again after charging the batteries and no luck. It doesn't work now. Could have to do with laser color?
navaburo (author)  youngdemetre1 year ago
Hey! I'm glad you got something, even of it was faint.

Are you using a mic input on the receiver side? A solar cell is self-powered, so it may not work well in a PC mic jack, which is expecting a varying resistance. Honestly I just don't know -- ive never tried it.

What you can do is, build or use a preamp after the solar cell but before the main amp. Be sure to use the "line in" jack on the main amp, not a mic jack.

If you want more help, I suggest you draw a schematic of your setup, and/or use pictures.
I figured it out. The solar cell I'm using was to big of an area for the laser. The dot from the laser wasn't big enough, luckily I was using a laser that also had a led light. The more area of light shown on the cell produced the sound, it's working quite well, I'll probably make something more about mine sometime.

Again thanks for your help.
Ok I figured out!! The solar cell I have has a larger area so I think that means it needs more light hitting a wider area. The laser I'm using also has a flashlight and i turned it on and it started working! Thank you again for your help hope you have a good night!!
NGinuity2 years ago
I assume you're using the transformer in that manner to "step down" the level of the input signal as well as modulate the DC going to the diode. Is that correct?
ALogan972 years ago
Is the audio transformer necessary? I forgot to buy one and don't want to go back out to radioshack to get one.
Zack12963 years ago
YA CAKE! btw the project is awesome
can you replace the laser with an led
That would be an Optoisolator...at least by the time you actually got the led close enough to eliminate noise and get an effective signal...but basically an optoisolator uses an LED coupled with a phototransisitor in order to electrically isolate the control circuit from the circuit being controlled.
i would seriously not recommend doing that will it work? yes is it effective? absolutely not an led is not a focused beam, cannot be used over long distances like a laser can, and it is more prone towards the distortion as the light is more spread out. The laser points light precisely at the photo diode, so that is the light which is converted to audio. Theoretically, using an led would require total darkness so as to eliminate that interference. Give it a shot and tell how it went!
XOIIO3 years ago
Could you just hook a laser diode to the audio output and a reciever to a microphone input? IT seems like it would make sense.
navaburo (author)  XOIIO3 years ago
Short answer, no.

This is mainly because laser diodes only conduct electricity in one direction - that is, they work with Direct Current (DC). However, (most) audio outputs have alternating directions of current (AC). So when you hook up a laser diode to the audio output, you only get half of the waveform.

Furthermore, laser diodes have a minimum voltage required to turn them on. So you will actually get less than half of your waveform if you attach the laser diode directly to the output.

That is why there is a battery pack involved: the batteries provide the direct current bias needed to keep the laser on. The audio output (via the transformer) subtly changes the strength of that direct current, and is therefore manifest in the laser's output brightness.

Hope that helps.
Warlrosity4 years ago
what is a duh? is it an iPod knockoff?
No. It is an IPod. It means that you need music. Your'e a duh! =P
jelte12343 years ago
actually: would ripping apart a wireless cheapy headphone not also work, and then replacing the leds with a laser? or is this a bad idea?
No the LEDs are in the transmitter, and they have a wide angle so your headset can receive from anywhere in the room. A laser transmitter has to point straight toward its receiver, in this case William Tell style
ep03173 years ago
Could you please specify the type of audio transformer that you used? thanks..
caseyC0884 years ago
would it be possible to make a two way radio sort of thing if you made two of these??
lazer1554 years ago
 Is the potentiometer absolutely necessary?  I dont have one on hand so I want to know if I can use just a resistor.  Can I use one of those photocells instead of the phototransistor?
navaburo (author)  lazer1554 years ago
Short answer: YES.

Long answer: if you knew exactly what resistance(s) to use, you could substitute the potentiometer(s) for fixed resistor(s). However, these resistances depend on your laser pointer and the voltage of your battery pack, so it is really convenient to use the pots. (They are inexpensive too.... and useful in other projects, so I'd recommend buying/salvaging some.)
 What is the potentiometer for?  I got it working without a pot or a resistor.  Does the pot filter out static and background noise?
navaburo (author)  lazer1554 years ago
Lasers often have a non-linear response. That is, their brightness depends on the power-supply voltage in a complicated way. The potentiometer(s) along with a control of the input audio amplitude (mp3 player volume) allow you to select which section of the psv-brightness curve to use. So, you should be able to select a linear portion, and get great audio quality. Using a non-linear portion will result in nasty sounding distortion.

Also, I realize now I didn't address your second queston "can you use a photocell instead of a phototransistor". I assume you mean either a Cadmium-Sulfide passive cell or an active solar panel (generates electricity from light). The issue with the photo-cells are that they (typically) have a slower responce-times as compaired to a phototransistor or photodiode. The result is that a photo-cell-based circuit does not pick up on the higher frequencies as well, if at all. It might sound like music through a wall (only bass).

But, you can always try origional designs! Do let me know how you get along with this!

Chris
lazer1554 years ago
 Also how would I hook this up directly to a speaker instead of having to put it in a mic port?
nice project
adhwaith4 years ago
hey... i don't seem to be able to get any music across... is there any way of testing if the transmitter works???? and i'm using a 10k ohm potentiometer, could that be a reason???
Firecrow4 years ago
when i point my laser beam at the reciever i get no sound.. Does this mean that my laser beam is not good enough? and if so could i just connect it to a infrared led?
navaburo (author)  Firecrow4 years ago
Firecrow, You can test the function of your receiver by holding the laser close to the receiver and quickly passing the laser beam across the photodetector. You should here a low-pitched WompWompWomp. If you are using the mic port on a computer to receive and amplify the signal, you can use a recording program (like Audacity) to see if the laser is being detected. If you hear/see the signal from flicking the beam across the detector, then you know the detector works, and you have to work on the transmitter. Best of luck and let me know how it goes! - Chris
Can you post some pics of the sensor lab?
UbuntuNinja4 years ago
My laser uses 3 button cell batteries (4.5 volts) so can i replace the 3 volts in the diagram with 4.5 volts to give the laser a reasonable brightness?
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