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[liberationtech] Efficient digital one-way communication

Yuval Adam yuv.adm at gmail.com
Sun Mar 3 06:52:22 PST 2013


I love this PoC, and I believe it might actually prove useful in certain situations.
Short-range FM transmission is certainly possible with cheap devices [1]
Modulating the FM signal should be a breeze, I'll try to hack up some code soon.
Awesome project.

[1] - http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter 

On Sunday, March 3, 2013 at 4:25 PM, Jens Christian Hillerup wrote:

> Hi,
> 
> One thing I've been thinking a lot about recently is how to make
> digital one-way communication feasible for activists, sort of sending
> digital information to the broad public. I believe that FM is a good
> medium for this because the transmitters are cheap and everybody has a
> radio. Hook up the radio to your sound card, and demodulate the audio
> back into data, and there you go.
> 
> I did a quick hack back in September, called modulera [1]. The idea is
> to exploit how pentatonic polyphony always sounds good, regardless of
> the notes picked (as long as they're within the scale). The way it
> works is that it takes three octaves of some pentatonic scale (in this
> case F# major), and silence. This gives 16 different notes. Split up a
> byte into two nibbles and you get your two tones. I realize this
> approach has a way too low bitrate, but I like the aesthetic in having
> the modulated data also be easy on the ears. For any real use, this
> would likely need to be scrapped to increase bitrate. Feel free to try
> the script, though! I've included the output of the script modulating
> itself.
> 
> I basically just wanted to throw it out here. Does anybody have
> experience in modulating data? Has this kind of digital one-way
> communication been done in an activist setting before? Does it make
> sense to kick off a project aimed at creating a easily usable system
> capable of modulating and demodulating data at modest bitrates
> (>15KB/s)?
> 
> JC
> 
> [1] https://github.com/jchillerup/modulera
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