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Audio over a laser beam
My latest project has been transmitting audio/sound over a cheap laser pointer. I found the original plans for this here.
The parts I used are:
1. Laser pointer level from Target
2. Cadmium-Sulfide Photocells (Radio Shack part 276-1657)
3. Audio output transformer (Radio Shack part 273-1380)
4. battery holder for 1 AA battery
5. battery holder for 3 AA batteries
6. Audio source ( I used the line out of my laptop)
7. Headphones
8. small piece of a dowel rod.
I picked the Target laser pointer level because it was the easiest to hack. First take the dowel rod and put a small nail in one end. Attach a wire to the nail. Put the dowel rod into the tube that holds the battery, then use a rubber band to hold it in place. Second attach a wire to the base of the laser pointer.
Take one wire from the laser pointer and attach it to one of the 1k leads of the transformer (blue wire). Take the second wire and attach it to the positive lead of the 3AA battery pack. The laser pointer usually runs on 2 AA batteries. With the transformer, the laser pointer would barely light up so I used 3 AA batteries instead.
The audio source needs to be attached to the 8ohm side of the audio transformer. Attach one line to the red wire and one to the white wire.
We now have a laser transmitter.
For the reciever take the 1 AA battery holder. Connect the positive lead to one end of the photocell. Take the negative lead and connect it to your headphone. Connect the other lead of the headphone to the other end of the photocell. We now have a reciever.
The sound goes into the transformer. The transformer then causes the laser to modulate. When the laser light hits the photocell, the photocell changes the amount of electricity going to the headphones. This causes the sound.
have fun.
Comments
law blogger:
This process of transmitting audio/sound over a cheap laser pointer is very creative and effective. Thanks for providing the list of parts used in this project. It will be great if you can provide similar information for transmitting video. file bankruptcy in houston
Anonymous:
Sam, please try this experiment, you will be surprised.
Still, a good experience.
Anonymous:
This is a terrible plan! If it works at all, well.... you really ought to have a proper amplifier driving the laser, or pulse-modulate it.
OTOH if it works it's a triumph of a 1910-style audio circuit driving a 21st century semiconductor laser.
If the microcontrollers elsewhere on the site can sample analogue at audio frequencies, and I'm sure they could, this would be a good project for one.
Read in an analogue sample, and transmit the binary, by flashing the laser, eg long-pulse (still in microseconds) = 0, shorter pulse=1. Then on the other end have a light-sensor, convert the digital back into analogue, shazam.
When transmitting the samples, you'd need to know where each one starts, otherwise it's just an endless beam of 0's and 1's. You could use a third, different length pulse to signify "start".
I don't think lasers modulate well in an analogue mode. The lasers used in professional links are all digital, pulses on and off.
Has the OP really made this? And got it to work? And didn't blow his laptop's sound chip?
Sam.
Anonymous:
Sam, not really, it works pretty well, good sound quality.
You are making the same mistake as lots of other people who think laser is digital.
In terms, a simple $5 key-chain-laser can be modulated with certain degree of quality in linear region. You can have almost 60% of the laser radiation level in semi-linear region. But when modulating a laser with a scheme here presented, the audio-transformer modulates the laser in less than 5% of its radiation range, so, the region is pretty linear. And more than that, linearity here is related to "amplitude" not frequency, it means that the sound may appear as if went through an expander, higher volume is a little bit higher than usual, while low levels would comprise a little bit. But this will only be noticed by those with great hearing, not my case, not 99% of the population.
And no, the sound you hear is not a 1910 style radio, it is very difficult to say if you have the earphones connected to the stereo or via laser.
The only great mistake people are doing is attaching a photo-resistor (LDR) as a receiver. The LDR is not a good receiver mostly for high-frequencies, the best option would be a photo-diode, op-amps to amplify the signal, etc. But the LDR is a very, very low cost bipolar solution.
Sam, please try this experiment, you will be surprised.
Still, a good experience.
:)
wagnerlip
Johhnyonthespot:
I'm about to try it out, sounds very feasible and it's not digital at all. You could technically use this for higher speed communications, if the cheap laser is able to modulate that fast...hmm...I'm glad I came across this.
Thanks!!!
it's time to put old lasers to use
Anonymous:
Hows the quality?
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