Thanks dillonjerry. Might there be any data present in the signal on the headphone jack if I am not putting out an audio waveform? ie. by virtue of the circuit passing through some of the data processing elements of the motherboard.
For instance in a way similar to the paper published here...
I'm playing around with an oscilloscope and my laptop's headphone jack. I get the tip/ring/ground and measure between them. I also measure between them and an external reference ground. I notice I can see when the battery is charging. That is, if the battery is not in the laptop but the AC is...