Hi,
Just curious if keeping it simple and using a resistive voltage divider to keep an input signal below the level that will damage a sound card, followed by a buffer >> sound card, can give reasonable results when using one of the common PC O'scopes (Visual Analyser).

I intend on using this for audio frequency waveform viewing (say, 100Hz - 10 or 15kHz); very little need for actual 'measurement' in any quantitative way. I'm looking for such things as the onset of clipping, phase differences, what different filters do to changing frequencies in the real world and that kind of thing.

I've read the large post from Bill Marsden et. al. where they try to create a 'real' input section...I'd like to go much more simple than that if possible, but have no real clue what the pitfalls are (beyond killing the soundcard). Like, what are the most likely things to get 'skewed' just because of the nature of the input? How am I going to be 'fooled', y'know...

Thanks for any information!

 

The worst thing that has happened to me was a ground loop from connecting the "grounds" of two power supplies when I was using my PC oscilloscope . The grounds weren't really at the same potential and one channel of my card got zapped. I was careful on the "hot" leads but it hadn't occurred to me to protect the ground connections too. Hard-learned lesson.

Otherwise I'm thrilled to have such a cheap but useful tool (a PC sound card oscilloscope) on my bench. I can see anomalies outside the audio range, but seemingly good waveforms in range. You do have to divide down any voltages above 5V or so but I suppose that depends on your specific card. I don't see clipping at 9V so for most things on my bench it's not a concern.

 

How did you solve the ground loop issue? Just curious. I think I'm going to build a buffer to avoid impedance issues / 'skewing' and give this a try...
I've run VA and have both channels taking signal - it's just making sure that what I'm seeing is reasonably accurate, ha ha...

 

I have tried some different softwares before, and I'm interested in memory function, but I'm not going to too deep, and I saw many samples for the applications, one person even modified it to became a DC measurable equipment, he just took the capacitor away from the sound card, and he also changed the resistance, but doing this way will make the equipment more dangerous.

Talking about the buffer, I just thought about the photocouple, when we measuring the sine wave that the interface will working in the liner area, when we measuring the pulse or square wave that the interface will working in the saturation area.

The photocouple should considering the voltage and frequency, the interface should have a voltage limited part as zener to protecting the computer device even the computer itself.