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Comment by vluft | Hacker News Reader

On a related note, the excellent DIY Perks youtube channel recently replaced toslink leds with lasers to do a wireless surround system https://www.youtube.com/watch?v=1H4FuNAByUs

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What happens when your sub starts kicking so hard that your walls start to vibrate causing the line of sight to go intermittent?

Then the audio drops out, so it's a self-correcting problem!

Also, the beam is a bit divergent, even if it vibrates the beam could still cover the sensor.

Not necessarily. The sub is not usually attached to a wall, so it wouldn't self correct like you're suggesting

I think you missed a joke there.

Loss of signal -> silence -> no vibrations -> signal resumption.

no, you're missing the point. the subwoofer is not connect to a wall that vibrates, so it wouldn't miss the signal. the surround speakers and possibly the front and surround speakers tend to be attached to a wall. The floor doesn't shake enough for the sub to loose alignment is the point.

Well, (to treat this seriously, rather than the joke it was) where's your transmitter? And are there vibration-sensitive components inside of either the transmitter or receiver? Several times a month, cars idle outside my apartment with bass loud enough to severely shake my windows, and somewhat shake my walls and floor. I imagine a receiver that's physically attached (or merely very near) to a subwoofer that loud would have trouble maintaining a steady optical link.

I was making a joke though.

Also, if you bounce the signal off a mirror on the wall like DIY Perks did, then walls vibrating even a little bit will be an issue if the beam is narrow enough.

What an excellent natural interpretation of "DROP THE BASS"

Next step, point a TOSLINK laser at the Moon Retroreflectors!

There was something posted not too long ago that bounced radio signals off of the moon that they then turned into an audio filter based on their testing on what it would do to the signal.

https://en.wikipedia.org/wiki/Earth%E2%80%93Moon%E2%80%93Ear...

I like the example audio file they have for the article, because the QSO ends with "73, bye bye" and that bounces off the moon and is received by the sender a little bit later. The moon is far away!

(I also really enjoy the distortion to SSB signals that you get by tuning the "carrier" frequency slightly wrong; more likely in this case because the moon changes the frequency of the reflected signal due to the doppler effect. Also happens with satellite comms, though you might not notice if you're using FM and not SSB.)

The dark side of the moon on continuous loop would be an interesting project.

The problem with DIY perks solution is that the manchester clock+data encoding is an amplitude modulated thing and isnt really very robust to using in free space. LED bulbs, sunlight, or all manner of other stuff can and will fuss with it. This is probably why he ended up having to go with lasers instead of just a big IR blaster against the ceiling. If he modulated the OOK signal onto some kind of carrier the entire thing would be a lot more reliable and as a bonus could probably ditch the lasers. This is more or less how the infrared wireless speakers and headphones of yore (80's and 90's) did the job.

So the problem with his solution is that he needed a solution to solve a problem?

It works but it's not going to be very robust without a carrier.

If you mean a literal “IR blaster”, those generally modulate onto a 38kHz carrier. (I built an IR blasting device out of a 555 timer and an LED once, and it worked great, and no, I did not use precision resistors or capacitors. I admit I’m not actually sure whether a standard IR blaster contains a modulator or whether the device supplying the signal is expected to pre-modulate it.). You’re not going to get anything resembling acceptable audio quantity over consumer IR tech.

> anything resembling acceptable audio quantity over consumer IR tech

I don't know what you are on about. You can go to your local walmart and get IR headphones off the shelf that work exactly this way.

Such a great video. There is a really good chance I use that technique for a remote subwoofer at some point. Really elegant solution.

A part of me wants to use his idea to set up some kind of wireless data connection just for fun.

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