Laser Audio Transceiver Project

In this project I’ll show you how to make a laser audio transmitter, a device that will allow you to take any sound source, and transmit it over a laser beam. With about $8 worth of parts and 15 minutes you can create one of the coolest, yet simplest electronics project that will be fun for the newbie and advanced hobbyist alike.

After seeing this project on quite a few project sites I’ve felt compelled to give it a try, however due to other commitments I rarely have the time for anything. When an option for an electronics project arose in Communications Technology class I spared no time in gathering my materials and started out to kill two birds with one stone.

Parts List

Transmitter



* A Cheap Laser Pointer
* Batteries and Battery Packs ( I suggest anywhere from a minimum of 4.5 to a max of 6 volts)
* Sound Source with an Output Jack (MP3 player, diskman, walkman)
* An earphone jack to fit the sound source
* An Audio Output Transformer consisting of an 8 ohm coil and a 1000 ohm coil. (Radio Shack #273-1380)
* Insulated Clips leads ( At least one being enough to fit inside the laser pointer)

Receiver



* A photo-resistor
* AA Battery and Pack
* A mono-microphone jack
* A device to take the sound input (Some radios, stereos, A PC w/ sound card)

Design & Concept

Transmitter

The transmitter will consist of laser pointer, batteries, and sound source which will turn the audio signal into light. The sound source will turn the audio into an electrical current to be transmitted over the jack, wire, and the transformer. This will vary the amount of resistance on the other side between the batteries and laser pointer, making the intensity of the light directly affected by the intensity of the audio. This process is called amplitude modulation.

Receiver

The receiver essentially works the opposite way. The photo-resistor will vary the amount of current between the batteries and the audio jack & source, depending on the intensity of the light it receives.

Fabrication Directions

Transmitter



Unscrew the end cap from the laser and remove all the batteries. Attach one of the clip leads to the inside coil of the pointer (it being the negative terminal) and another clip lead to the casing of the laser (it being the giant positive terminal), making sure it has contact with the metalic coating inside. To test the laser with the external battery pack first attach both leads to the pack, if the laser doesn’t work try reversing them.

Once you have ensured the correct terminal arrangement connect one clip lead to the battery pack in its working order, and connect the other to the 1000 ohm side of the transformer. Connect the remaining wire from the battery pack to the same side of the transformer. (Note: This side of the transformer has 3 wires, the middle wire is called the center tap, which is not used in this project)

The opposite side is rather simple, connect the 2 wires from your earphone jack to the 8 ohm side of the transformer.

Receiver



The receiver is ridiculously simple. Connect one of the wires coming from your microphone jack to your battery pack, and the other to the photo-resistor, then connect the remaining end of the photo-resistor to the other end of the battery pack.

I think the easiest way to test the receiver is to simply plug the circuit into the microphone jack in your computer and run ‘Audacity’ (A free ware audio editor), start recording and experiment by turning on and off the lights, or waving your hand over the photo-resistor. If connected correctly you should see and hear the audio/current being produced by the variations in light.

Implementation

Plug your receiver into the device with speakers, such as your computer. You will have to turn your speakers up until you hear a hissing noise as the audio volume tends to be rather low.

Connect your sound source, such as your mp3 player into the transmitter and aim it at the photo-resistor. Press the button on the laser or hold it down with something such as an elastic band and try to hold it steady. If done correctly your tunes should be traveling as light waves and playing to your ears enjoyment.

If not, try adjusting the volume of your speakers up, or the volume of your sound source down, my transmitter will not transmit terribly loud bass. Also it would be a good idea to double check and solder your connections. Turning off the lights may be the only option when using this device, since sometimes the interference caused by household lights is too great.

Conclusion

This nifty project is a fun and cheap way to transmit audio in a dimly lit room, it is way more affordable than expensive wireless speakers. However modifications and improvements will need to be made to this design in order to take this project idea and put it into a practical use.

Improvements that could be made are:

* Using a tripod to hold the transmitter steady
* Using a more expensive laser pointer could be used since the $1 model may not have the same range and signal strength
* Putting the circuits in small project boxes for aesthetic reasons and protection
* Making a guard to shield the photo-resistor from outside light interference.

I refrained from making these improvements since I had to leave the circuits cheap, open and visible for my class presentation and for this article.

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