Adam Bryant wrote:

> 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
>

It is important that you clamp the input. I do not know exactly the input
range of the mic and if it accepts negative voltages.
The diode clamps are imporant BUT they must be connected to the maximum
voltage of the mic input.

If you are really interested, send me the complete specifications of the mic
and I will try to design a good buffer input. What I need to know is the:

-- Maximum allowable voltage on the mic
-- Wether the mic accepts -ve signals

Joseph A. Zammit