Forums

DIY PC Oscilloscope

Started by Unknown March 9, 2013
On 3/10/2013 2:44 PM, John Devereux wrote:
> nico@puntnl.niks (Nico Coesel) writes: > >> Francesco Poderico <francescopoderico@googlemail.com> wrote: >> >>> On Sunday, 10 March 2013 00:16:57 UTC, Bruce Varley wrote: >>>> <francescopoderico@googlemail.com> wrote in message >>>> >>>> news:c1ad2481-696a-4257-8242-a8c92169124b@googlegroups.com... >>>> >>>>> Hi all, >>>> >>>>> I've started designing a 200 MSPS Oscilloscope with a 25 MHz analog >>>> >>>>> bandwidth, 3Ksample/channel buffer. >>>> >>>>> The oscilloscope can be connected to a PC via USB, and eventually via >>>> >>>>> Ethernet and WiFi. >>>> >>>>> The trigger is ( at moment) rising, falling... auto, normal. >>>> >>>>> >>>> >>>>> I would appreciate suggestions and or comment for possible improvement >>>> >>>>> and functionality that could make this oscilloscope interesting. >>>> >>>>> >>>> >>>>> Thanks, >>>> >>>>> Francesco >>>> >>>> >>>> >>>> Been there done that. Spent many weeks putting together a box that I was >>>> >>>> very proud of, then purchased a Rigol that does everything it does plus a >>>> >>>> lot more and a lot better. Is this really a good use of your time and >>>> >>>> energy? >>> >>> I get the point... and your are not the first one to tell me that. >>> but I believe that an oscilloscope is still an instruments a lot of electronic enthusiastic would love to have it if priced correctly. >>> Marketing will be the biggest challenge in a market so competitive. >> >> Did you look what a Siglent scope costs on Ebay? IIRC its about US >> $180 including shipping from China. How do you expect to beat that? >> BTW Lecroy sells the exact same scope for a lot more. > > I've wanted to make something like a "dynamic signal analyser" that goes > up to 1 or 10 MHz, instead of 100kHz like they all seem to.
You and me both. I'm fond of my HP 35665A, but like the rest it only goes up to 100 kHz. (It also uses a somewhat wimpy digitizer--13 bits or something--but a bit of the old HP magic makes it work very well anyway.) There have been a few FFT spectrum analyzers where you could use the IF section as poor man's DSA, but it would sure be nice to have all the features of a real one, at 100 times wider BW. (Of course I'm way too cheap to actually buy one, unless I had a real genuine customer requirement.) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
 Jeff Liebermann  wrote:
>6. Presumably, it's dual channel. If so, make it stackable via a >common bus or preferably via ethernet, so that multiple units can be >conglomerated into a 4,6,8, etc channel scope.
From my (rather narrow) point of view, where the main use of an oscilloscope is in debugging embedded software, this would make it stand out above the competition. -- Roberto Waltman [ Please reply to the group, return address is invalid ]
On Sunday, 10 March 2013 21:25:43 UTC, Roberto Waltman  wrote:
> Jeff Liebermann wrote: > > >6. Presumably, it's dual channel. If so, make it stackable via a > > >common bus or preferably via ethernet, so that multiple units can be > > >conglomerated into a 4,6,8, etc channel scope. > > > > From my (rather narrow) point of view, where the main use of an > > oscilloscope is in debugging embedded software, this would make it > > stand out above the competition. > > -- > > Roberto Waltman > > > > [ Please reply to the group, > > return address is invalid ]
Thanks Roberto, I'm not sure what do you mean with a stackable oscilloscope, do you mean... e.g. 4 oscilloscopes... 2 channel each that makes a 8 channel oscilloscope? The only problem I see with that is that between each scope you can have 20 ns max. of time offset.
On 3/10/2013 3:43 PM, Francesco Poderico wrote:
> > Thanks Roberto, > I'm not sure what do you mean with a stackable oscilloscope, do you mean... e.g. 4 oscilloscopes... 2 channel each that makes a 8 channel oscilloscope? > The only problem I see with that is that between each scope you can have 20 ns max. of time offset. >
Wouldn't it be easier to pass the trigger between modules ?? Getting one signal right would be easier then getting 4-8-12 signals right. My $0.02
Francesco Poderico  wrote:
> Roberto Waltman wrote: >> Jeff Liebermann wrote: >> >> >6. ... so that multiple units can be >> >conglomerated into a 4,6,8, etc channel scope. >> >>... this would make it >> stand out above the competition.
>I'm not sure what do you mean with a stackable oscilloscope, do you mean... e.g. 4 oscilloscopes... 2 channel each that makes a 8 channel oscilloscope?
That is what I understood from Jeff's post.
>The only problem I see with that is that between each scope you can have 20 ns max. of time offset.
That could be unacceptable in some scenarios, and not important at all in others. May be you can add a common clock or some other HW trick to synchronize several units? -- Roberto Waltman [ Please reply to the group, return address is invalid ]
Francesco Poderico <francescopoderico@googlemail.com> wrote:

>On Sunday, 10 March 2013 21:25:43 UTC, Roberto Waltman wrote: >> Jeff Liebermann wrote: >> >> >6. Presumably, it's dual channel. If so, make it stackable via a >> >> >common bus or preferably via ethernet, so that multiple units can be >> >> >conglomerated into a 4,6,8, etc channel scope. >> >> >> >> From my (rather narrow) point of view, where the main use of an >> >> oscilloscope is in debugging embedded software, this would make it >> >> stand out above the competition. >> >> return address is invalid ] > >Thanks Roberto, >I'm not sure what do you mean with a stackable oscilloscope, do you mean... e.g. 4 oscilloscopes... 2 channel each that makes a 8 channel oscilloscope? >The only problem I see with that is that between each scope you can have 20 ns max. of time offset.
If you distribute the trigger and use a global reference clock to which all the ADCs are synchronised it will work. At least that is how I planned it for my own USB scope design about 9 years ago. But then Rigol emerged so I stopped the project. -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
"Nico Coesel" <nico@puntnl.niks> wrote in message 
news:513d21d9.4118857421@news.kpn.nl...
> If you distribute the trigger and use a global reference clock to > which all the ADCs are synchronised it will work. At least that is how > I planned it for my own USB scope design about 9 years ago. But then > Rigol emerged so I stopped the project.
You still have the propagation delay of the clock (and trigger if shared) cascading between modules. You could characterize each unit's delay and adjust in the DLL, perhaps, or perform a round-trip self-calibration, or ask the user to run a BNC cable from the "probe test" connector on the master unit down to each successive input; assuming the cable remains constant during the test, this would allow the inputs to be adjusted for zero time difference. Tim -- Deep Friar: a very philosophical monk. Website: http://seventransistorlabs.com
On Monday, 11 March 2013 00:48:33 UTC, Tim Williams  wrote:
> "Nico Coesel" <nico@puntnl.niks> wrote in message > > news:513d21d9.4118857421@news.kpn.nl... > > > If you distribute the trigger and use a global reference clock to > > > which all the ADCs are synchronised it will work. At least that is how > > > I planned it for my own USB scope design about 9 years ago. But then > > > Rigol emerged so I stopped the project. > > > > You still have the propagation delay of the clock (and trigger if shared) > > cascading between modules. You could characterize each unit's delay and > > adjust in the DLL, perhaps, or perform a round-trip self-calibration, or > > ask the user to run a BNC cable from the "probe test" connector on the > > master unit down to each successive input; assuming the cable remains > > constant during the test, this would allow the inputs to be adjusted for > > zero time difference. > > > > Tim > > > > -- > > Deep Friar: a very philosophical monk. > > Website: http://seventransistorlabs.com
Thanks to everybody for the suggestions, I will think about... as it could be a good selling point... I'm a bit concerned regarding the clock syncronization between different FPGA, at 200 MHz it's not easy and you can have easily have 1 or 2 clock skews between modules... I need to think about
On Sun, 10 Mar 2013 13:17:23 -0500 Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in Message id:
<843%s.276931$J13.102560@newsfe08.iad>:

[snip}

>Yeah, but it has Lecroy's name on it and that's like GOLD!!!!!!!!!!!
I dunno... Every time I pick one up on the surplus market, they sell poorly and for low $ compared to a Tek or Agilent of similar specs. There are guys who will buy nothing else *but* Lecroy, but they seem to be a very small group compared to Tek and Agilent fans. Consequently, I haven't bought one in over a year, I end up sitting on them too long. One thing positive I will say about them, I've never seen a 93XX or LC series scope alias, where as Tek and Agilent scopes of similar vintage are very easy to get to alias.
"JW" <none@dev.null> wrote in message 
news:jhirj8h7ach6hj7nlc2fllel66n94ptf2t@4ax.com...
> One thing positive I will say about them, I've never seen a 93XX or LC > series scope alias, where as Tek and Agilent scopes of similar vintage > are > very easy to get to alias.
Not necessarily an advantage -- in the old days, of course, the analog trace simply looked fuzzy due to any modulation that was too fast to resolve, or not harmonically related to the trigger source. On digital scopes, it's best to have the option. Many times I've looked at a signal and thought, "where did it go?" Zooming in, it shows up. Tek's "high res" mode, I think, does a crude oversampling IIR effect, which looks very nice around traces with much noise or ripple (clearing away noise I would have trouble cutting through otherwise), but also misses that information. Speaking of noise, it aliases too, correct? As long as the bands are uncorrelated (to each other; correlation to the sample rate I don't think matters, as long as it's still "noisy"), it should go as V = Vo*sqrt(B / (2*Fs)), given a noise source of full-bandwidth amplitude Vo, bandwidth B, and sample rate Fs. But then, random sampling has to have the same statistics as the source signal. I seem to be forgetting something. Tim -- Deep Friar: a very philosophical monk. Website: http://seventransistorlabs.com