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Soft Modem

2011-09-29 16:42 electronics, supercollider

This summer I build 8 small circuits that can control a bunch of LEDs (6 channels PWM) from basically any iDevice or Android phone. The circuit connects to the audio jack of the phone and uses the right channel to send data commands (in the form of a modem signal).

We use rjdj (and Pdlib, SuperCollider, etc) to generate the data signal on the phone in realtime. And it's relatively easy to connect for example the built-in accelerometer in the phone to control some LEDs, or to run amplitude/pitch tracking on the microphone and let that flash some LEDs.

The circuits will be used in the rhyme research project as well as in the upcoming e-textile workshop in Oslo (Oct 2011).

The design is based on SoftModem by arms22. Attached below are my schematics, Pd FSK abstraction and Arduino firmware.

The modem signal is generated using Frequency-shift keying and here's how to do that in SuperCollider...

c= "how are you?";
{var t= 1/1225; var m= Duty.ar(Dseq([t*100]++t.dup(11*c.size)), 0, Dseq([1]++c.ascii.collect{|cc| [0]++(cc.asBinaryString.ascii-48).reverse++[1, 1]}.flat), 2); SinOsc.ar(m*(7350-4900)+4900)!2}.play(fadeTime:0);

This will send the characters "how are you?" at a baud rate of 1225. This is of course not a valid command for the circuit above, just something to demonstrate how it sounds. Below is an MP3...


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