Depending on the transfer function of the audio output system, it may be possible to simply shove moderate rate non-return-zero encoded data through it by delivering PCM samples to the audio driver, and recover it with an appropriate receiver circuit on the other side.
What is certainly possible is to implement a low rate modem using frequency shift keying between two audio tones, or more complicated phase and audio modulation constellations, and recover that. For a limited set of discrete functions, sending DTMF type tones and using a DTMF receiver IC or algorithm is another possibility. On Mar 1, 7:24 am, Earlence <earlencefe...@gmail.com> wrote: > but playing sound is different from controlling a device right? > or they just send data bytes which are control signals for the > external device :) (instead of sending pcm data) > > Cheers, > Earlence > > On Mar 1, 12:38 pm, Stefan Schake <caytc...@gmail.com> wrote: > > > Hey, > > > because user space apps are allowed to play sound? You certainly don't > > get a perfect digital signal but its apparently good enough. > > > Greetings > > > 2011/2/28 Earlence <earlencefe...@gmail.com>: > > > > Hi, > > > > I have seen from this app (http://www.squareup.com) that they are > > > driving an external device thru the headset jack with just a userspace > > > app. > > > I have checked the kernel sources and seen htc_35mm_headset.c and > > > htc_headset.c which contains driver code for the HTC 2 Wire protocol. > > > Its my understanding that to drive a custom device, a custom driver > > > would be needed. and to replace a driver, root access is required. How > > > is that app then able to drive a device on the headset jack from java > > > userspace? > > > > Cheers, > > > Earlence > > > > -- > > > unsubscribe: android-kernel+unsubscr...@googlegroups.com > > > website:http://groups.google.com/group/android-kernel > > -- unsubscribe: android-kernel+unsubscr...@googlegroups.com website: http://groups.google.com/group/android-kernel
