Recently there have been discussions about using a PC soundcard as a
cheapo oscilloscope.  I have found a number of excellent looking sofware
applications for this purpose, but not wanting to take a chance at
blowing up my sound card, I was wondering what the typical specifications
for a soundcard microphone input were.

I was also starting to put together ideas for a circuit I could put
between the tested circuit and the sound card to protect it from any
nasties generated by the tested circuit.  The idea I had was as follows:

                                        +5v
                                        |
                                        |
                                      Diode
                                        |
                                        |
Input signal -------Res-----Res---+---------OpAmp--------Sound Card
                                        |
                                        |
                                      Diode
                                        |
                                        |
                                        Gnd

The OpAmp is wired as a unity gain (voltage follower).  An EE friend of
mine told me that would provide very high input impedance.  This is the
same basic circuit I was planning on using in my own DSO (whenever I get
the time to build it).

Thoughts?  Suggestions?  Is this a reasonable way to go about this?  Is
there a better way?

Thanks in advance,
Adam


Adam Bryant (age 0x23)
abryant@peaktech.com (work)
adamdb@juno.com (home)
Parker, CO, USA
Robotics, RC Airplanes, anything using a PIC

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