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

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A single audio channel can theoretically produce a 38,000 Hz signal for infrared (IR) transmission, but traditional audio devices typically cannot reproduce such high frequencies. The discussion references a Griffin patent that suggests using two audio channels to sum frequencies, which has been confirmed to work on a PC but not on a phone, where only one LED emits IR light. The distinction between symmetrical output and standard left/right channels is highlighted, raising questions about waveform outputs at various pins when playing a 38,000 Hz signal. The conversation also clarifies that amplitude modulation of an IR carrier signal occurs at frequencies higher than audible, making it challenging for standard audio devices to achieve this. Overall, while the concept is feasible, practical implementation varies significantly based on the device used.
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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.
 
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