using your PC as an O-Scope

[Andy]

I found some software, Ozsi, but how do you interface from your circuit to the PC?  Special probes to MIDI?  Where do you get the interface?

[Rob Strand]

I've reviewed heaps of them and I can't remember if I've seen that one before.

You make your own probe by connecting some wire-ups to the line-in inputs of your sound card but there's a better way (see below).  Of course you have to set-up the sound-card mixer so it records from line-in.

I've thought about suggesting these on the group in the past but I've been reluctant for two reasons:  The first is the triggering is generally poor, and so they are very frustrating to use compared to a real CRO. You also have to make sure you aren't overloading the sound card inputs, otherwise the display is garbage.  The second is it's quite easy to blow-up your sound card.  Beginners slip-up all the time and blow stuff up, it's all part of the game, but blowing-up a $150 sound card is a lot of chips worth of mistakes.

If you want to use these I suggest not using a direct wire for the probe.  Instead connect two red LEDs in anti-parallel between sound-card input and ground, then a 4.7k resistor in series with the probe lead.  This will give a good deal of protection to the sound card- as a bonus the LED glow under severe overload.

Yet another way is to build a simple one-opamp preamp, or buffer, and place that between the sound card and the probe wire.  You can add protection to the preamp bu keep the LED protection between the preamp and the line in as well.   The idea behind using this is you at worst blow your preamp opamp instead of the sound card.

[Rob Strand]

I've drawn up a schematic for a simple probe,

http://homepages.ihug.com.au/~rstrand/yadda/PC_Line_Input_Protection_v10.png

[peterc]

There is some excellent free software over here  :

http://www.dazyweblabs.com/shannonsoft/page3.html


Peter

[peterc]

There is some excellent free software over here  :

http://www.dazyweblabs.com/shannonsoft/page3.html


Peter

[Rob Strand]

Thanks Peter, that software looks great - I'll download it and check it out.