Interface Circuit for PC Soundcard Oscilloscope

For simple electronic circuits, it may be sufficient to get a qualitative insight on dedicated electrical signals. This interface circuitry allows to use the line-in input of a standard PC soundcard to be used as a 2-channel oscilloscope. This setup does not allow for exact measurements, however for some applications, a qualitative insight on dedi

cated timing or signal characteristics may be obtained. The interface limits the signals from input channel 1 and 2 to a maximum amplitude of 1. 2 V (over-voltage protection circuitry). At the left side of the schematic below, the two input channels for signal measurement and the common ground are shown. At the right side, next to the protection diodes, the connections for the 3. 5 mm stereo jack to the soundcard (line-in) are drawn. The height of the signal amplitude shown within the OSZI can be adjusted with the two trimmers with signal of known amplitude (e. g. a rectified 5V signal). Since most line-in are AC-coupled, pure DC signals are not suitable for calibration of the voltage levels. Note: There exist now very nice software tools for your PC soundcard (Windows XP) from Sebastian Dunst: AudioAnalyzer & MultiSine. See the software section.

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