| Author |
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Davide
Guest
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 Posted:
Thu Dec 08, 2005 4:02 pm Post subject:
Re: USB digital scope |
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I'm sorry, I'm not sure that the DLL works in this envronment. I
checked the DLL only with delphi and Visual Basic. I think this can
work also with Visual C++.
The A/D is the ADS805 or ADS807 from TI. (the price is the same and the
second has 50 MSPS smaple rate).
hi,
Davide
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Rene Tschaggelar
Guest
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| Posted:
Thu Dec 08, 2005 5:06 pm Post subject:
Re: USB digital scope |
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David L. Jones wrote:
| Quote: | Check out the cleverscope for a nice USB scope that has 4MB of sample
memory (SDRAM). It trys to compete with the Agilent mixed signal scopes
and actually doesn't do too bad a job:
http://www.cleverscope.com/
The software (Labview) lets you do lots of clever custom programmable
maths directly on the waveforms too.
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Labview is the killer. Did you ever spend a month
trying to bring the wires through some silly walls
while knowing with some decent compiler it would
have been a matter of minutes ?
Rene |
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David L. Jones
Guest
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| Posted:
Thu Dec 08, 2005 5:35 pm Post subject:
Re: USB digital scope |
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Joel Kolstad wrote:
| Quote: | "Marte Schwarz" <marte.schwarz@gmx.de> wrote in message
news:dn4qtr$jov$1@news2.rz.uni-karlsruhe.de...
The PCB is intended to mount also two 12 bit 50MSPS A/D converter (I do
not yet tested this A/D converter but I hope this works fine...) in
place of the two 12 bit 20MSPS; The PCB has an "expansion port" for a
daughter board for:
3. To stack multiple board in order to have 4,6 or 8 channel scope.
I've thought about doing something like this myself on and off, but there's a
couple of challenges with the approach:
-- Aligning all the paths from one box to the next pretty much implies that
you need to generate a common clock somewhere and distribute it to all the
individual boxes with some known relation from box to box. If you do restrict
people to physically plugging one box into the other (or connecting them only
with cables of known lengths that you've provided), this is not difficult.
-- You need to distribute a high speed "trigger" signals to all the boxes so
they know when to stop capturing. That's not too hard, but what's harder is
that you have to consider whether or not you want every box to be able to
trigger or whether you just want to have a specialized "trigger" box... the
problem is that, while repetitive random-time sampling is great (with
repetitive signals), your trigger circuitry has to operate at the "equivalent
time" rate, i.e., much faster than the ADCs themselves.
-- With digital (logic analyzer) boxes, it becomes challenging to start
coordinating triggers when the trigger event is something like, "bit pattern
1010xxxx on box #1, then 00xxxx00 on box #3, back to xx0xxxxx on box #1,
etc..." (And this is a very simple trigger event compared to what contemporary
logic analyzers can do.)
At the end of the day I figured it's be easier just to design one big PCB and
populate it differently based on the options a user wants, just like the big
boys do. :-) I think there's a huge market out there for a USB-based
instrument that implements most of what something like a Tektronix TDS3054
does -- 4 analog channels, 500MHz analog response, 5GSsp. With '3054s going
for $10k, if you could profitably sell a USB-based version for, say, $2500,
you'd have more orders than you could fill, I imagine!
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I suspect not.
Those after that sort of performance would most likely not want a USB
based scope, they want a "real" scope they can play with on the bench.
500MHz analog bandwidth is incredibly difficult to do, and at 1GS/s+
you need to roll your own ADCs which is what the big scope
manufacturers do. That takes massive R&D time and $$$$$$$
You can't just slap together a bunch of parts from Digikey and get
anywhere near that performance.
| Quote: | The Bitscope guys (www.bitscope.com) out of Australia have been quite
successful, even though their products are nowhere near as fancy as a TDS3054
(they're basically 100MHz/100Msps with ONE channel and something FAR less with
two channels).
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They aren't as fast as the real scopes because you can't go much above
that with off-the-shelf parts.
Dave :)
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David L. Jones
Guest
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| Posted:
Thu Dec 08, 2005 5:35 pm Post subject:
Re: USB digital scope |
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Davide wrote:
| Quote: | You're perfectly right. My goal was a 100$ instrument and not 1000$
instrument!!! The comparison is not from instruments in the same
"segment".
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Yes, you are right.
It is a great design for the price, although the lack of memory really
cripples it, regardless of how cheap it is. I suspect more people would
happily pay double or triple the cost for say a 1MB scope, or even 10KB
worth of sample memory.
How much does a few MB of SDRAM cost in order to get a vast improvement
in functionality?
I've seen inside the CleverScope, and it is not much more than 2 SDRAM
chips, an FPGA, and the input circuitry. Pretty pricey, but volumes are
low and it fills a niche.
Dave :) |
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David L. Jones
Guest
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| Posted:
Thu Dec 08, 2005 5:35 pm Post subject:
Re: USB digital scope |
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Rene Tschaggelar wrote:
| Quote: | David L. Jones wrote:
Check out the cleverscope for a nice USB scope that has 4MB of sample
memory (SDRAM). It trys to compete with the Agilent mixed signal scopes
and actually doesn't do too bad a job:
http://www.cleverscope.com/
The software (Labview) lets you do lots of clever custom programmable
maths directly on the waveforms too.
Labview is the killer. Did you ever spend a month
trying to bring the wires through some silly walls
while knowing with some decent compiler it would
have been a matter of minutes ?
|
Yup!
I love it how supposed "specialists" can't even explain how their
Labview "code" works, nor can they fix the damn thing 12 months later
because they can't understand what they did. Love it how you can't
readily "peer review" it either.
And NI push it like it's the greatest thing since sliced bread and what
wonderful benefits it has for our organisation, all we have to do is
send every one of our programmers on the Labview BASICs course and
we'll all be instant experts :->
Dave :) |
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Joerg
Guest
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| Posted:
Fri Dec 09, 2005 1:35 am Post subject:
Re: USB digital scope |
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Hello Riscy,
| Quote: | I think it do need 12 bits, it give better range and resolution to do
some post calculation.
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Yes, if you want to do FFT and stuff like that. But I thought this
thread was more about the scope nature of a digital scope. When you want
to use it to track down runt pulses, phase jitter, setup and hold
violations and the other usual stuff the ADC needs to be as fast as can
be. Even if that comes at the expense of bits. I have done quite some
work with 6-bit digitizers because that's all we had in them days when
you needed more than 100MSPS. We actually needed 400MSPS. The ENOB up
there had probably been 4 bits or less but it did the job.
Regards, Joerg
http://www.analogconsultants.com |
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