Although it "sounds" weird... it is possible: http://www.freepatentsonline.com/6931231.html Application: http://jumpjack.wordpress.com/2008/06/10/turn-your-phone-into-an-universal-remote-control/ You can convert an audio file into an infrared signal which can control your TV set! But I've a couple of questions, don't know if this is the best place to ask them: - why can a phone with "symetrical audio output" (???) reproduce a 38000 HZ signal, knowing that any audio device can usually reproduce only up to 20000? - is it possibile to reproduce a 38000 Hz signal using a MONO audio output rather than a stereo one? I did some studies, and the result is "yes"... but when I do it, I don't ger results I waited! Excel spreadsheet Image I think that the opposite parts of the audio wave get "summed up" when they're converted into light, thus doubling the output frequency. But actually I see only ONE led transimitting light. Why?!?