Sound transfer… BY LASER : DIY Experiments #3 LASER light music wireless

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• Text of the video :

Hi everyone, in the video we’ll transmit a music using a LASER on 442 meters. We invite you to watch the video in its integrality because we are first going to present our creation and try on a short distance then we will try on a very large distance. At least we will explain how is work and do some tests with the LASER’s power.

To transmit a music we need an emitter, a receiver and between both, as you guessed, a LASER beam. Concerning the emitter we will explain to you how it works at the end of the video. Using it is pretty simple, we plug the jack to a device, here we have a switch to light the LASER and here we can choose the modulation level, from low to high with an intermediate. To aim the receiver which can be really far we need an extra high precision, that’s why we’ve created a stuff precise at a 77th degree from top to bottom and from left to right.
Currently the receiver is a guitar amplifier with a high gain, it is linked by jack to a mini solar panel. The LASER we use has a 250 mW power, which is about 200 times more than classical LASER trackers. In order to see the LASER beam on the camera we use a mini fog machine.
We have separated devices within a few meters, we set the amplifier on a 10th of the maximum volume…
A quick test with the synthesizer…

On the LASER we have the possibility the use a lens to change the light propagation angle. However after 442 meters even with the smallest dot possible it is never under 10 cm large. To remediate, we use a solar panel block composed with four little solar panels on derivation, we can put it this way.

Now, we are going to try the transmitting on 442 meters. We have to bring the emitter to our friend Kevin who lives there. Ok, we are at Kevin’s, the emitter is set up, the LASER is put on the maximal power then we just have to aim with the best accuracy one of those houses!
After a quarter of an hour at least, it’s done. Let’s start music and plug in the jack, modulation level is maximal, let’s go for the transmission!
Here is what we can see 442 meters away! The LASER is very bright even with the sun. Good job, we can see a red dot on the wall where we’ll put solar panels. Solar panels are directly linked to this 250W amplifier. With the high gain of this stereo, small light variations are very well transposed!

All is ready, let’s start the emitting… And it works!
Bad luck, because of a pine just in front of the LASER we have strong volume variations. We’ve put the solar panels a little bit higher, let’s try with max volume!
Please, Kevin,, move your fingers just in front of the LASER beam. Ok, that was predictable!

We can notice that with the volume max we hear a sound about the wind one especially on long distance like here. This sound comes both from dust in the air and turbulences linked to heat.
To create the emitter we used only basic and recovered electronic components. It is the same for the wooden planks. Nevertheless, we bought the LASER on eBay but you can also craft a powerful one with a DVD writer and lens. The concept is based on the variation of the LASER’s power at the rhythm of the music. The easiest way to do this is to use a ferrite core with two wires. This way the alternating current from the music will cross the ferrite core and impact the LASER’s power. This principle is workable until a 5mW LASER but no more because the modulation level is very low. In the actual project we use a 1 to 25 ratio transformer follower with a bipolar transistor. As a result the music variations are strongly amplified. The LASER is used at 80% of its maximal power so when there is a positive impulse it light brighter and less bright with a negative musical signal.
On the other side it is simpler. The solar panels are constantly producing power due to the LASER or the sun. This continuous power is eliminated by the amplifier’s filter. It is only the variations of light from the LASER that are amplified so we can hear the music. Obviously, between the emitter and the receiver, the musical signal is transmitted at the velocity of light. Contrary to fiber optic networks the transmitting is only analogical, and the signal is necessarily damaged.
We also use a 5 V regulator in used to allow the LASER to light as bright no matters the battery state of charge. By the way our lead battery holds hours of transmission.