Re: gEDA-user: Any DIY USB Scope project on schedule? Or somerecommmendation?

[Olgierd Eysymontt <olgierd.eysymontt@multical.cl>]

Velleman builds electronic kits including two very cheap portable
scopes, you can buy them assembled or as a kit.

I don't have at hand the manufacturer website but below you can find a
store link.
http://www.elexp.com/tst_ps40.h

Apogee kits sells them also.

Olgierd Eysymontt

El mar, 23-11-2004 a las 21:50, Daniel Nilsson escribió:
> On Tue, Nov 23, 2004 at 07:40:31AM -0800, Samuel A. Falvo II wrote:
> > On Tuesday 23 November 2004 05:00 am, Xtian Xultz wrote:
> > > this produtc says it makes 20M samples per second, but have a analog
> > > bandwidth of 250k Hz. What is the greatest (in frequency) signal I can
> > > measure with it? Someone knows?
> > 
> > If the analog bw is 250kHz, then you can expect accurate representation 
> > of waveforms up to 50kHz (square waves will have harmonics all the way 
> > out to and beyond 250kHz).  If you are just observing sine waves, then 
> > 250kHz would be your top frequency.
> 
> Regarding square waves, the frequency of the square wave doesn't
> matter from a measurement perspective. What matters is the rise and
> falltime of the signal that you are measuring. To calculate the BW
> based on the risetime a good approximation is BW=0.35/tr where tr is
> the fastest out of rise or falltimes. For example, is you signal has a
> 10ns risetime, the bandwidth requirement would be 0.35/10e-9 =
> 35MHz.
> 
> Now this 35MHz bandwidth only allows you to measure a 10ns edge
> correctly, if you are interested in any glitching/ringing or so you
> need to oversample this signal. Depending on who you ask (scope
> manufacturers are most conservative...) you get answers between 3 and
> 10 times. But somewhere in the 3-5 range i probably OK. So in reality
> you asking for 5*35MHz=175MHz bandwidth to look at a digital signal
> with 10ns edge rate (which is very slow with todays standards). The
> sampling rate then needs to be at least twice of that ( > 350Ms/s ).