Side channel on the headphone jack

[keystroke]

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 in, then I insert the battery, it runs through some software or something in the battery for a few seconds and then if the battery is not full, it goes to a waveform - if it is full, it goes to another "quieter" waveform.

I am just doing this for fun. Can anyone think of interesting experiments I can do? I would like to see about extracting signal from the noise of the waveform.

Thanks!

 

[dillonjerry]

You can download a signal generator program. That would let you output various waveforms from the computers audio card. Depending on the type of scope you could also try to pick up the RGB sync signals from the computers VGA output. There are a lot of things you could look at.

 

[keystroke]

You can download a signal generator program. That would let you output various waveforms from the computers audio card. Depending on the type of scope you could also try to pick up the RGB sync signals from the computers VGA output. There are a lot of things you could look at.

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:
https://www.defcon.org/images/defco...on-17-barisani-bianco-sniff_keystrokes-wp.pdf
or
http://cs.tau.ac.il/~tromer/acoustic/ (Here the noise comes from a bank of 1500µF capacitors).