Q:

How to measure a dc or ac signal using PC as oscilloscope?

I want to measure for ex a battery 0.7V dc using a program like Visual Analyser/Soundtrack Oscilloscope/jDTF/Scope/xoscope. I connect the negative pole of the battery to sleeve and the pozitive to ring 

But I dont see any changes on soundtrack oscilloscope. I tested it with microphone on the same plug in and it was respondign to my voice, but when I plug in the dc voltage nothing is changed, there is only noise. Do you know what am I doing wrong?

A:

There are differences, you can't get DC into a sound card as everybody is telling you. Hopefully you can see the differences here. 
Oscilloscope probes also have a much better bandwidth than a 3.5mm cable. The oscilloscope also has an "amplifier" to gain the signal.

simulate this circuit – Schematic created using CircuitLab

