Low-Cost USB Oscilloscope

[T.Jackson]

@500MHz with 2G samples / second -- that's only 4 sample points. Without black magic, how in the world could you capture much with that? (might suffice in purely the digital domain, certainly won't capture glitches though)

[Darrel Taylor]

that's only 4 sample points. Without black magic, how in the world could you capture much with that?

I don't really know. But I thought if the "Golden Rule" of 5x would work,
maybe silver was ok too.

And I guess I'm also trying to figure out what it would take to do the original post.

Assuming you want a 5Mhz "Bandwidth". Which way do you mean?
5Mhz bandwidth? Or 5M samples/sec?
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[T.Jackson]

I don't really know. But I thought if the "Golden Rule" of 5x would work,
maybe silver was ok too.

And I guess I'm also trying to figure out what it would take to do the original post.

Assuming you want a 5Mhz "Bandwidth". Which way do you mean?
5Mhz bandwidth? Or 5M samples/sec?
<br>

When I say x5 -- I generally mean that, if you consider 100MHz to be your highest point of measurement, then ideally you'd probably be best of with a 500MHz scope. I think though however, this old saying is more applicable to analogue scopes than anything.

5MHz bandwidth for a DIY scope? -- personally, I'd be chasing 20M samples / second or more.

[T.Jackson]

But without complex software algorithms (that I don't know enough about yet) -- I estimate the usable bandwidth to be about 1MHz @ 20M samples / second.

[T.Jackson]

This statement has a lot to do with it I feel ...

The fundamental AC waveform is the sine wave, a square wave is made up of a multitude of many, many, sine waves. We certainly have a square wave @ 500MHz w/ 2g sample / second.

Question is; how do we extract it?

[T.Jackson]

Qualified engineers like; Melanie & Jerson should have little difficulty in answering this.

[T.Jackson]

Maybe trade secret? :|

[Jerson]

Qualified engineers like; Melanie & Jerson should have little difficulty in answering this.

Trent,

I got into this thread a little too late. However, I do not understand the question you're asking here.
BTW : I have used a Parallax USB based scope in one of my designs and more recently a Velleman scope. Their bandwidth was stated to be 20MHz, but the highest frequency we could reasonably see would be around 100KHz IIRC. Its been a while since I did this, so my information may be of the mark. The 20Msamples/sec happened to be the sample rate. For repetitive signals, it becomes easy to reconstruct the waveform with higher resolution by staggering the sample points wrt the zero crossing of the waveform. However, the low cost PC scopes that I have used did not seem to have this feature and just took snapshots.
This seemed to be the pattern for acquisition
Pre Samples -> Trigger -> Samples -> Ready is signalled -> display is refreshed -> repeat the cycle