DIY PC Oscilloscope

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

Reply to
francescopoderico
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3Ksample/channel buffer.

and WiFi.

functionality that could make this oscilloscope interesting.

It will have 5 ns p-p trigger jitter, unless you do tricks, which would be interesting.

Are you using an FPGA? Even low-end parts usually have more memory than that.

The hard part is the front-end, attenuators and such.

You can build a scope with nasty transient response, untweaked attenuators and such, and fix the response in the PC software.

What's the cheapest comparable thing on the market now? Your parts cost might be in the $40 ballpark, maybe even at 50 MHz.

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John Larkin                  Highland Technology Inc 
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Reply to
John Larkin

On a sunny day (Sat, 9 Mar 2013 10:22:38 -0800 (PST)) it happened snipped-for-privacy@googlemail.com wrote in :

3Ksample/channel buffer.

and WiFi.

functionality that could make this oscilloscope

Add TV:

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Reply to
Jan Panteltje

this is the blog of the oscilloscope:

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Reply to
Francesco Poderico

this is the blog of the oscilloscope:

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Reply to
Francesco Poderico

width, 3Ksample/channel buffer.

hernet and WiFi.

and functionality that could make this oscilloscope interesting.

e

In theory is possible to have a 5 ns p-p trigger jitter, but only when the noise floor is less then 0.5 LSB, otherwise you need to add some form of hi steresys that will increase the jitter opening. but in theory is possible

hat.

I'm using an FPGA for triggering and buffer. at moment a small device, as I'm quite impressed with the results (tomorrow I will post a video on my bl og) next revision I'm planning a SPartan 6 with external memory IF.

Correct, I have spend 2 months or maybe 3 just to design the analog parts, I must admit I believe I have over designed, but i'm very happy with the re sults so far. My plan is to measure and publish the analog bandwidth.

s and

The scope has a compensated attenuation in the front end that seems doing a good job. Therefore there is not needed for SW tricks. I personally don't like

ight be

I think the Picoscope 200 series is the main competitor, which is around 20

0£ + VAT
Reply to
Francesco Poderico

Why only 25MHz? Yes it's easier, but the ADC probably has an analog bandwidth in the GHz. Why waste it?

My TDS460 has 100MSa/s and 350MHz bandwidth. For periodic signals, it's as good as an off-the-shelf MSO or DPO series (arguably better since it doesn't have that retarded DPO crap you can't turn off), which usually claim something ignorant like 5GSa/s and a mere 100MHz.

As John says, the attenuator is the hard part. Perhaps you could pilfer them from old analog or digital scopes, and feed the output to your ADC and trigger generator.

Tim

--
Deep Friar: a very philosophical monk. 
Website: http://seventransistorlabs.com
Reply to
Tim Williams

3Ksample/channel buffer.

and WiFi.

functionality that could make this oscilloscope interesting.

There are plenty of similar USB scopes on the market with similar specs. Use their feature list as a checklist to see if you're missing something. I presume that you're asking for advice on how to make the hardware unique in order to obtain a marketing advantage. Most of the product differentiation is in the software, so I'll comment only on the hardware. What *I* might want in a USB scope is (whether I'm willing to pay for these is another question):

  1. USB microscope camera on the probe tip so that I can see where I'm sticking the probe.
  2. IR thermometer with LED targeting on the probe so that I can simultaneously measure and record any localized heating.
  3. Replacable front end so that when I inevitably blow it out, it can be easily replaced.
  4. Built in function generator, pattern generator, arbitrary waveform generator, two tone generator, DDS generator, white/pink noise, sweep generator generator. Extra points for adding AM/FM/PM/pulse modulation.
  5. DC power output for powering active probes and assorted sensors.
  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.
  7. Switchable low pass filter on input for high RF level environments.
  8. Self test and calibration check.
  9. An accurate and readable schematic so I can fix it.
  10. Security cable to keep it from getting um.... borrowed.
  11. Built in smoke detector.
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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

Thanks Tim, good point, Actually in theory I could use the DLL inside the FPGA and changing the clock phase with a resolution of 25 ps... so in theory I have a 1 GSPS FPGA for repetitive signals! Do you think it would make more attractive to buy? Actually the maximum bandwidth is 70 MHz, I'm low filtering for aliasing.

Reply to
Francesco Poderico

bandwidth, 3Ksample/channel buffer.

Ethernet and WiFi.

functionality that could make this oscilloscope interesting.

Thnanks Jeff, I like the idea of the Cable that stop "unwanted borrowed" I will actually do this... not sure about the camera on probe :-)...

I may add a block diagram ( notthe full schematic) to show people how to calibrate the scope and some test points and hits to help people to self repair the scope.

also the function generator, could be a good sales point

Thanks

Reply to
Francesco Poderico

Nah, 25ps resolution means you can take acquisitions shifted in time every

25ps -- 40GSPS equivalent! But, do beware of the manufacture and temperature variation of the delay. FPGAs are made for worst-case timing constraints, and anything that's adjustable (like a DLL) is put inside a loop (hence, DL*L*).

Heck, make it better than a Rigol, from cheaper parts. And open source it (if it's that kind of project). Create shock waves in the marketplace! ;-)

My TDS460 says "50GS/s ET" (Equivalent Time) on 1ns/div. Looks like it's actually filling the whole screen with that resolution, not just interpolating between samples.

The 100MHz, ~10MS/s HP54600B goes down to 1 or 2ns/div or something like that, but it uses sinc interpolation on such fine scales. I don't know what a Rigol does for high sampling rates.

If you skip antialiasing filters, you get sharper displays and equivalent time sampling. If you filter, you're basically saying: "Yep, I purchased this 200MS/s ADC, and the FPGA to run it, and I'm taking both of them over to the grinder and shaving off... ohh about 80% of the silicon, because... I like the smell?"

Filtering basically negates the trigger generator, too. You could sample continuously and do the trigger digitally instead. Which...

...I think for any particular period between trigger crossings, you'd want to use some sort of interpolation to adjust the timing -- sample N is a bit below the threshold, and sample N+1 crossed the threshold by so-and-so and caused a trigger, so we know the dV/dt and can estimate where it *did* actually cross. So we can stack this sample period on top of the other, which crossed at whatever rate, by aligning it. Shift everything sideways by the calculated time difference, using a suitable interpolation (a simple quadratic spline would be reasonable, but a sinc interpolation might be more physically significant), then stack it up for display.

The "stacking" itself could be an array of buffers (so you have a memory of many traces, and can perform statistics on them to generate the display -- decimate (view only one), average (which would now be a FIR "sliding average", which AFAIK, no scope manufacturer ever does for averaging mode!), peak detect, median, RMS + std dev., etc. This display process could, of course, be done for either acquisition method (continuous or triggered).

But again, such hackery, though interesting, doesn't get your bandwidth back, it's just software diddling for not being clever enough to get the bandwidth and trigger right in the first place. :)

Tim

--
Deep Friar: a very philosophical monk. 
Website: http://seventransistorlabs.com
Reply to
Tim Williams

ndwidth, 3Ksample/channel buffer.

Ethernet and WiFi.

ent and functionality that could make this oscilloscope interesting.

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y do this... not sure about the camera on probe :-)...

calibrate the scope and some test points and hits to help people to self re pair the scope.

the first thing I would add is USB isolation (data and power) so that when using usb and/or powering it from usb the scope is isolated from the pc

-Lasse

Reply to
langwadt

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?

Reply to
Bruce Varley

bandwidth, 3Ksample/channel buffer.

a Ethernet and WiFi.

ement and functionality that could make this oscilloscope interesting.

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lly do this... not sure about the camera on probe :-)...

o calibrate the scope and some test points and hits to help people to self repair the scope.

Good point, I was thinking to use an ADuM5xxxx from AD.

Reply to
Francesco Poderico

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.

Reply to
Francesco Poderico

enthusiastic would love to have it if priced correctly.

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.

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Failure does not prove something is impossible, failure simply 
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Reply to
Nico Coesel

enthusiastic would love to have it if priced correctly.

Yeah, but it has Lecroy's name on it and that's like GOLD!!!!!!!!!!!

:) Jamie

Reply to
Jamie

enthusiastic would love to have it if priced correctly.

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.

High dynamic range (16+ bit) low noise, with arb generator.

I've got one of these, and I like it, but it is a big old slow beast of a thing:

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John Devereux
Reply to
John Devereux

electronic enthusiastic would love to have it if priced correctly.

it's challenging but not impossible. I agree...It is very difficult to compete with China, but not impossible if we point on quality.

Reply to
Francesco Poderico

electronic enthusiastic would love to have it if priced correctly.

point on quality.

If you think the Chinese can't make quality stuff then you've made your first big mistake. If its good enough for Lecroy to stick their badge on the quality bit is in order.

So re-think your competitive edge. Remember that a good DSO is 5% hardware and 95% software. So even if you get the hardware right you are still nowhere near a sellable product.

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Failure does not prove something is impossible, failure simply 
indicates you are not using the right tools... 
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Reply to
Nico Coesel

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