Sending Music Long Distance Using A Laser

This isn’t the first time we’ve seen DIYers sending music over a laser beam but the brothers [Armand] and [Victor] are certainly in contention for sending the music the longest distance, 452 meter/1480 feet from their building, over the tops of a few houses, through a treetop and into a friend’s apartment. The received sound quality is pretty amazing too.

In case you’ve never encountered this before, the light of the laser is modulated with a signal directly from the audio source, making it an analog transmission. The laser is a 250mW diode laser bought from eBay. It’s powered through a 5 volt 7805 voltage regulator fed by a 12V battery. The signal from the sound source enters the circuit through a step-up transformer, isolating it so that no DC from the source enters. The laser’s side of the transformer feeds the base of a transistor. They included a switch so that the current from the regulator can either go through the collector and emitter of the transistor that’s controlled by the sound source, giving a strong modulation, or the current can go directly to the laser while modulation is provided through just the transistor’s base and emitter. The schematic for the circuit is given at the end of their video, which you can see after the break.

They receive the beam in their friend’s apartment using solar cells, which then feed a fairly big amplifier and speakers. From the video you can hear the surprisingly high quality sounds that results. So check it out. It also includes a little Benny Hill humor.

And when have we seen laser communication before? Why yours truly demonstrated a shorter range transmission using a dollar store pet toy laser sending to a solar cell and homemade amplifier. If you want to dig deeper, Gigabit laser Ethernet is the one for you.

47 thoughts on “Sending Music Long Distance Using A Laser

  1. Reasons you might want to dick around with this… get some long distance laser experience for when quantum networking gets DIYable… send the paired photon to buddy across town and data teleport between systems faster than a machine accessing it’s own RAM.. (Quantum onboard interconnects SHOULD replace all system buses, but we’ll see) .. providing of course that your method of interfacing doesn’t slow it down, USB 3.0, external SATA, 10 Gbit ethernet or whatever other slowass antiquated shit you’ll be using that pushes actual electrons down actual conductors.

    1. Though speed of light limits causality to within the light cone, none of this quantum entangled FTL(simultanious across town) data we were all hoping for, not a big deal to you or me harassing a cat with a laser dot, but light speed gets syrupy slow when you factor in modern computers and fast data speeds and modulations with protocol timeouts and such. Not to say you can’t do the q-bit shared processing thing though once we are better at it.

          1. Garbz – Here in the STATES we get a lot of aircraft bird strikes. Mainly geese. We have a new movie based on one in Hudson River NYC called SULLY (2016). A commercial airliner had geese fly into turbofans and they had to ditch the aircraft in the river. All souls survived.

    1. Agreed and then some. There are people in the area, too. This is a Class 3B laser. Blink reflex is way too slow to be safe, and at visible red (633nm I’m guessing) the damage is via retinal burn, so that’s permanent with no hope of repair.

      I’m all for clever experiments and trying out new things, but this gets a bit too close to the old saying: “Your freedom to swing your fist ends before the tip of my nose.”

      1. Considering light scatter, they get less dangerous over the distance. At 20 meter they should be safe as a 5mW laser, but divergence of the laser has a big impact on distance.
        At a safe height i’d see them no different than high kV power transmission lines.

  2. I didn’t expect a sound that clean from a solar panel: they once were quite slow to respond to light variations. Using a photodiode/transistor paired with a preamplifier with sub 20 Hz filtering (to save woofers) would improve things a bit, but then it couldn’t be done with parts salvaged from toys or garden solar lamps:)

  3. Canon has used a laser as a “Network Interconnect” between two buildings divided by a highway.. Cheaper than paying the city to dig up the street and run fiber. Works great.. It even cancels out the distortion of wind/smog/rain etc. I’ve even seen the demo while attending Interop in Vegas.
    The send/receive units even cancel out building sway..

  4. That toroid has very poor low frequency response. The thumping in the speakers is not bass but DC air distortions. There is no DC coming out of whatever audio source you are using. Just be sure to put a 100 ohm load on the output and then couple it to the driver. A FM carrier would eliminate the DC problem, and allow for stereo.

      1. There is a cap already in the audio output, it’s in the source. Just put a light resistive load on to bleed off any DC. Any DC on the output would ruin headphones on any player. The cap you want to add needs this done anyway. There is often a DC path to ground in the load (resistance) but not always if it’s to work with DC levels.

      1. RW – Except the “angle of the dangle” principles means the listener must be in a straight line directly across the street to get the bounce back. Not everybody can purchase optical-metamaterial reflectors on Ebay. Nor have the nerve to trespass on someone’s property at night to plant (glue) it on the target window. Also double plane windows are a challenge.

  5. One thing about running this via Amplitude Modulation… it tends to overdrive the laser-diode on peaks. It’s best to modulate the laser with PCM to avoid this. You could get pretty good range with a jumbo LED and photo-diode and Fresnel lens than a LASER. See the link below for verification of that.

    Also the long range record for a laser QSO was 118+ mile (>190km) in 1963.
    [Mike Szczys] did a HaD article on this May 14, 2013 – “Retrotechtacular: First laser transmitter built 50 years ago”. (It wasn’t actually the first laser transmitter, but it was one of the earliest.)

      1. Hirudinea – Too late. Ask your FILP’s (“friends in low places”) about the once classified USN S.L.C.* system. It uses a B-G LASER system and can penetrate a few feet of seawater. I’m pretty sure it’s a geosync and not LEO. The Japanese have one too. You can see one in mobile land-based mode operation in the movie The Objective (2008). It’s jam proof and pretty much 100% high bandwidth 2-way comm from anywhere on the planet (there’s obviously more than 1 geosync SLC bird). Notice in the video I posted how NASA’s version can find the source ground-based LASER and aim back at it for return.

        * Note: Please tell your FILP’s it’s plausible existence has been open-source since 1983 when B-G LASERS were invented. And DARPA was asking milindcmplx for a working airborne prototype in 2010. In 6-years it must be 100% operational by now.

          1. citrusfizz – I am not sure. Are you talking about the NASA video I posted? In that LASER COMM system, the ground-based source LASER is aimed at the target spacecraft with a diverged LASER (i.e. wide beam). The spacecraft’s omnidirectional LASER detector see’s it and a monopulse tracking system tracks the source for the strongest signal in that general direction. When that is achieved the spacecraft’s return LASER turns and illuminates in that direction. It too has a diverged LASER so that it probably has a large circle on the target rather than a pinpoint one. The initial response time must be into the several minutes area versus fractions of a second. But after that initial lock-on phase the video response time is at the speed of light through a mixed medium (i.e. vacuum and atmosphere).

            The several minutes response time is because the source LASER could be from anywhere on Earth the spacecraft is visible. So the monopulse tracking system would have to turn through several degrees of az-el to lock-on the source LASER. And then the return LASER has to turn to those bearings. However the monopulse tracker and the RETURN LASER could be mounted on same turret which would reduce the time to lock-on.

        1. citrusfizz – Also, since ISS is in LEO (low earth orbit) and not geosynch (geosynchronous), the monopulse tracker has to keep moving to keep the two LASER systems in synch. A monopulse system is a tracking system that moves in azimuth and elevation (az-el) on a gimbal-turret mount automatically to keep a source signal in focus. Monopulse RADAR tracking system was invented by USN in the 1943.

    1. Yep, I hear what you’re saying. We don’t have an “audio hacks” category so I generally put all of those in the “digital audio hacks” category. I think that’s way too specific for a category but it’s been around forever so… legacy. At some point there will be a great culling of superfluous categories. But it’s not as trivial as you might think. If you’re going to do it, the category set you end up with needs to be well thought out. Also, any categories that go away or change names need redirect rules set up.

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