Since you are limiting your range to between +5V and GND, you aren't going
to
get too decent a scope.  I would at least generate a -5V supply so the
signal
is centered around zero as audio is.

I would use the parallel port and a resistor divider network to ensure the
input signal stays well within your opamp rails.  Your mic input already has
a high impedance circuit, so you could probably just get away with the
resistor
divider network anyway.

Craig


> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Adam Bryant
> Sent: June 24, 1999 8:30 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [OT] Sound card input electrical specifications
>
>
> 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
>
> ___________________________________________________________________
> Get the Internet just the way you want it.
> Free software, free e-mail, and free Internet access for a month!
> Try Juno Web: http://dl.www.juno.com/dynoget/tagj.
>