Can a single audio channel produce a 38000 Hz signal for IR transmission?

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SUMMARY

The discussion centers on the feasibility of generating a 38,000 Hz infrared (IR) signal using a single audio channel instead of the traditional two-channel setup. The original Griffin patent indicates that two audio channels are necessary to sum frequencies for this purpose. However, the author successfully demonstrated that a single audio channel can produce the desired IR signal when applied to a PC, but not on a mobile phone. The conversation highlights the differences in audio output configurations, particularly with "symmetrical output" phones, and the implications for amplitude modulation of IR carrier signals.

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  • Familiarity with audio signal processing and frequency generation
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  • Basic electronics principles related to LED operation and audio output configurations
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jumpjack
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Sounds weird, but it is possible: you can obtain an infrared signal starting from an audio signal, and viceversa:
http://jumpjack.wordpress.com/2008/05/20/worlds-cheapest-remote-control-replicator-just-1/

But I miss something:
the old Griffin patent states that to produce a 38000 Hz signal using a 20000Hz audio output, you need to connect two IR leds to two audio channels, in such a way their frequencies sum up. Ok, it works; but I want to understand if same task can be accomplished with one single audio channel rather than two.
Somebody says it is impossibile; but I did this study:
http://www.planetmobile.it/jumpjack/ir2audio.xls"
http://www.planetmobile.it/jumpjack/immagini/ledrem.JPG"

It looks like it should work.
Actually, it DOES work, if applied to the PC; but it does not if applied to my phone: in that case, only ONE led emits IR light, and I can't understand why.

Besides, I have a phone which is said to have "symetrical output", which is quite different from standard left/right channels output:
http://pinouts.ru/CellularPhones-Nokia/nokia_pop_pinout.shtml"

I'd like to include in my Excel sheet explanation about this phone, but I can't: any help? Which waveform results at L+, L-, R+ and R- pin upon playing a 38000 Hz sinusoidal signal?
 
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I think the jumpjack article refers to the fact that the amplitude modulation of an IR carrier signal occurs at audible frequencies. That's different from heterodyne downconversion (or upconversion).
 
Andy Resnick said:
I think the jumpjack article refers to the fact that the amplitude modulation of an IR carrier signal occurs at audible frequencies. That's different from heterodyne downconversion (or upconversion).
no, it occurs at frequency far higher than audible: almost double! (38000 Hz rather than 20000).
So, usual audio devices cannot reproduce them; but they can reproduce half the frequency (19000 Hz), and combining two devices outputs, you can obtain 38000 Hz frequency.