anyone got source code for this one they would share ?
I really wanted to do a hardware solution, but damned if I can't find a source in North America for any of the ICs for this purpose.
On the surface this seems simple so maybe everyone is doing it in software now and hence the lack of hardware solutions.
I figure if I AC couple the audio to the analog comparator in one of the AVRs, and use that to detect zero crosses, that is all the hardware needed. I would use a couple clamp diodes as well just to make sure the levels stayed reasonable.
Then as far as software I am not quite sure - I can figure out how to detect the sum frequencies if they were the only thing present, not sure how the difference frequencies will affect the zero crosses. Possibly I should incorporate a highpass filter as well ....