
Ultrasound Networking (2014) - funspectre
https://www.anfractuosity.com/projects/ultrasound-networking/
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dheera
Is this protocol significantly different from what 56K modems do over an
analog phone line? How would the bandwidth compare to taking the 56K modem
protocol and upping the frequency to whatever band is used here?

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smaddox
I'm going to guess this guy doesn't have any dogs :-D

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raverbashing
It would be fun to try this with a 96kHz audio card (audiophiles, this is your
moment!) and trying this with a large band like 20kHz-40kHz (you would need an
ultrasound transducer and amplifier, of course)

You could probably get, I dunno 200kbps?

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namibj
Actually, there are 192 kHz sound cards.

As an example, I just picked the first microphone from mouser who's datasheet
includes ultrasonic spectral response. In this case it's a roughly 3 _2_ 1 mm
package with the acoustic port in the middle of the annular ground pad, likely
requiring a hole/via below. [https://www.mouser.de/ProductDetail/PUI-
Audio/AMM-2738-B-R?q...](https://www.mouser.de/ProductDetail/PUI-
Audio/AMM-2738-B-R?qs=zhx2xqPtQQyuc2nfUlDL7A%3D%3D)

Here's the datasheet:
[https://www.mouser.de/datasheet/2/334/AMM-2738-B-R-1761381.p...](https://www.mouser.de/datasheet/2/334/AMM-2738-B-R-1761381.pdf)

It is not nearly as flat above 8 kHz as below, but it's between -35 and -28 dB
(V/Pa) in the 20 to 80 kHz range. Nominal sensitivity is -38(+-1) dB (V/Pa)
between 20 Hz and 8 kHz. What this means, is that a 24bit 192 kHz ADC with
relatively flat response and no extra pre-amp should recover most of the SNR
(specified at 64 dB(A) SNR 1kHz 94 dB @ 50cm).

I expect it to work well with a normal TRRS "smartphone" jack, just connecting
the output via a decoupling capacitor to the sleeve and using the phantom
power. The TRRS compatibility guess is based on the numbers given in this
comment: [https://www.epanorama.net/blog/2014/09/15/android-device-
ext...](https://www.epanorama.net/blog/2014/09/15/android-device-external-mic-
wiring/comment-page-1/#comment-1460917)

Assuming one could exploit 60 dB SNR over the 60 kHz wide band, the
Shannon–Hartley theorem says there'd be a ceiling of 1.2 Mbit/s. Spectral
efficiency would be 20 bit/s / Hz, and for the SNR range above ~10 dB, (dB
SNR)/(bit/s /Hz) equals 3.

Your 20 kHz to 40 kHz band would actually give a nice 400 kbit/s with 60 dB
SNR, or 200 kbit/s with 30 dB SNR. The ultrasonic speaker for these
frequencies can be just a normal piezoelectric horn with either a crude
class-A audio amplifier who's low-pass filter was suitably adjusted/removed,
or a more efficient class-D device that can handle the relatively high
frequencies. Considering the rather high lower end of the required band, a
simple digitally-fed bipolar current source with pulse-density modulation fed
to the tweeter should be sufficient.

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yourad_io
Great demo using GNURadio, which I personally find daunting.

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canada_dry
A more recent use of ultrasonic is how cheap wireless cameras get their
initial configuration i.e. ssid/pwd.

Cheap and clever method for short range, low throughput. I'm surprised makers
haven't found creative ways to utilize it.

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Causality1
Networking that doesn't use ethernet cables or Wi-Fi is always fascinating.
I'm reminded of the way some labs in the pre-wifi days used infrared beacons
and transceivers on laptops to create local wireless networks.

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cerberusss
Oh gosh, I remember in college, playing with PCMCIA cards in laptops, and
you'd have to kinda point them at each other. Can anyone confirm if that could
be correct, or that I'm actually misremembering something?

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rasz
I wasnt familiar with any dedicated IRDA PCMCIA cards ever existing. But
apparently IBM made one :o

[https://www-01.ibm.com/common/ssi/ShowDoc.wss?docURL=/common...](https://www-01.ibm.com/common/ssi/ShowDoc.wss?docURL=/common/ssi/rep_ca/6/897/ENUS194-436/index.html)
or [https://groups.csail.mit.edu/mac/ftpdir/thinkpad/old-
archive...](https://groups.csail.mit.edu/mac/ftpdir/thinkpad/old-
archive/HTML/tp-1994/msg01797.html)

only picture I could find of one: [https://www.ebay.com/itm/0934340-IBM-
INFRARED-WIRELESS-PCMCI...](https://www.ebay.com/itm/0934340-IBM-INFRARED-
WIRELESS-PCMCIA-ADAPTER-NOS-0933878-/142052774528)

Still you wouldnt be aiming whole computers with pcmcia cards in them, there
was a dongle, most likely with a clip or velcro to slap in on the back of
laptop screen.

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voz_
I wrote something like this for Uber, except for Android and iOS. It was very
fun.

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dang
Discussed at the time:
[https://news.ycombinator.com/item?id=7255035](https://news.ycombinator.com/item?id=7255035)

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jaybna
Whatever happened to that company trying to transmit power via ultrasound?

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namibj
Dave Jones from EEVBlog made a debunking video on uBeam. They apparently tried
to to do ultrasonic wireless charging, which seems to fit your description.
Here's the video, it's mostly about efficiency/coupling loss (beam forming has
it's limits) and IIRC also about being potentially harmful for humans:
[https://www.youtube.com/watch?v=A8dqzVlhFkA](https://www.youtube.com/watch?v=A8dqzVlhFkA)

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jaybna
Yep. UBeam. Wonder what is left of all that money?

