Traditional Scope versus PC-based Scope - Page 1
Forum section: electronics / testgear

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: April 02, 2014, 08:54:18 pm
content: I'm looking for a new oscilloscope and, as always, the choices seem to be wide and varied.Is there any disadvantage of going with a PC-based scope, such as a Picoscope 6000 series instead of a traditional stand-alone scope such as an Agilent or Tek?Since PC-based scopes don't make knobs, buttons, and displays, they are less expensive than standalone scopes for the same specs. For example, the Agilent DSOX3024A scope is 200 MHz, 4 GS/s, 2 Mpts buffer for US$4200. The Pico PS6403C is 350 MHz, 5 GS/s, 512 Mpts for US$4500. The equivalent Agilent 350 MHz DSOX is US$7800.

author: w2aew
author_rank: Super Contributor
timestamp: April 03, 2014, 02:19:00 am
content: Quote from: Sal Ammoniac on April 02, 2014, 08:54:18 pmFor me, a PC based scope is too inconvenient to use to justify the lower cost. I don't want to have to have my computer on the bench when working on something. When poking around a circuit, I want to be able to quickly spin a few knobs to adjust the scope rather than grab a mouse or keyboard. Maybe I'm old fashioned (well, I know I am), but I'll never have a USB scope brick on my bench.

author: EEVblog
author_rank: Unknown
timestamp: April 03, 2014, 02:41:03 am
content: What Alan said.Plus the fiddling around with the app, using the mouse etc, having your virus scanner pop up in the middle of it, harder to move around to your job etc. A PC based scope is just not the right tool for a general purpose job that needs a scope.

author: miguelvp
author_rank: Super Contributor
timestamp: April 03, 2014, 03:21:15 am
content: This PC based scope surely is nice 160GS/s 62GHz BW and you can watch Netflix on ithttps://www.eevblog.com/forum/testgear/video-demo-experiments-with-the-world's-fastest-oscilloscope!-(the-signal-path/Of course I kid.

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: April 03, 2014, 05:55:36 am
content: All good points. Thanks. I'll probably stick with a traditional scope with knobs.Just how much scope bandwidth is "enough" for working with microcontroller projects? I mainly use ARMs running at around 100 MHz. Most of the peripherals are a lot slower (I2C, SPI, CAN, etc.) however. Sure, I'd love to have a 1 GHz scope, but my hobby budget won't allow it.

author: Mark_O
author_rank: Frequent Contributor
timestamp: April 03, 2014, 06:50:35 am
content: Quote from: Sal Ammoniac on April 03, 2014, 05:55:36 amObviously, "enough" will vary from user to user. But if your ARM processors are anything like the ones I work with, that 100 MHz is all internal. These are primarily controllers, after all. I think the fastest signal I've seen on the outside of the chip has been 50 MHz SPI, which turned outnot to actually work(25 MHz was the real Max, and the vendor had to errata it).Then it depends on what it is you want to be able to see. If you just want to verify presence of a signal, and its frequency, you may be able to get away with a bandwidth twice as high as the signal itself. If it's just a sine, 1x may be enough, since at the BWL the amplitude will have dropped by only 3dB. But if it's a square/pulse wave of some type (what you'll be working with 99% of the time), you probably want to see something where the edges are visible, and not looking like a sine wave.In that case, you want at least 5x for a good idea of the shape. But 10x to really be able to evaluate where the edges truly are.That may be important when tracking down timing issues, where the transition point is dependent on where something happens on a leading or falling edge. Less than 10x, and you'll only be guessing (which sometimesmaybe good enough, and sometimes, given financial constraints,has to begood enough).So the short answerwould be, 10x if you can afford it, and 5x if you can't. Based on the signals you'll actually be examining, NOT the internal clock speed of the chip.(Unless it brings out address and data lines to external memories... then we're talking about a different $$ context, though the same rules apply.)

author: David Hess
author_rank: Super Contributor
timestamp: April 03, 2014, 08:55:08 am
content: My workbench is cluttered enough without adding an extra mouse, keyboard, and display for a PC based instrument. I use carts for my oscilloscopes as it is now.Maybe the Picoscopes are different but the PC based instruments I have tested in the past had poor user interface performance.I would also be concerned that the lack of galvanic isolation between the instrument and PC places more hardware at risk in the case of a serious ground loop failure.As far as bandwidth, consider the probing difficulties. Up to 100 MHz, standard inexpensive x10 probes are easy to use. At higher frequencies, passive probe loading becomes significant (10pF at 200 MHz is 80 ohms) and ground lead length becomes an inconvenient limitation. Unless you are probing low impedance circuits coaxially, it becomes easy to spend as much on probes as on the oscilloscope itself to take advantage of high bandwidth.

author: jpb
author_rank: Super Contributor
timestamp: April 03, 2014, 10:39:24 am
content: The following is an interesting read if you're looking for a new 'scope (though it is getting a little old now) :http://www.embeddedrelated.com/showarticle/117.phpI read it before buying my 'scope and ignored most of the advice (I ended up with a 350MHz WaveJet which does not have high res - but I've been very pleased with it apart from a noisy fan and the fact that my model doesn't have the USB port to talk to my pc).The above article doesn't consider Rigol who probably offer the most bang-for-buck either.

author: TiN
author_rank: Super Contributor
timestamp: April 03, 2014, 10:59:04 am
content: QuoteWhen I first read topic title first thought was about "PC-based" Tek 7000, which ain't exactly less expensive, and have knobs, buttons and display.Need portable unit to check signals or do basic debug? Get USB dongle scope. Need something for lab bench - get real scope.

author: EEVblog
author_rank: Unknown
timestamp: April 03, 2014, 11:07:30 am
content: Quote from: Sal Ammoniac on April 03, 2014, 05:55:36 amNothing external on that micro works at 100MHz. Maybe 10MHz tops.Any regular 70/100MHz entry level scope will do you just fine.

author: HKJ
author_rank: Super Contributor
timestamp: April 03, 2014, 12:31:17 pm
content: I prefer the PC based solution and have used it for many years (I went directly from CRT to PC scope).I like the small footprint (The PC is not extra for me, it has always been on my workbench).The PC scope do have limitations, some are due to the limited speed of the usb connection, but you do also get function with PC scopes that are extra for stand alone scopes. I am using two pico scopes and they have added functions over time, without extra cost of me. A few years back pico scope did not have protocol decode function, but due to software update all pico scopes now has, including old models.

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: April 03, 2014, 03:43:12 pm
content: Quote from: HKJ on April 03, 2014, 12:31:17 pmThanks for the comments. Since all of my projects are MCU based, I've always had a PC on my bench to run the IDE/debugger (Rowley Crossworks for ARM), so it wouldn't be a stretch to also run the scope software. I use a PC-based logic analyzer (Saleae Logic and LeCroy LogicStudio), so I'm already running some PC-based tools on my bench.The Pico 6000 series is USB 3, so that should give it an edge over USB 2 devices. The Pico 6000 has lots of internal memory (512 Mpts), which is much more than the typical Tek or Agilent scope in the same price range has, and this memory is inside the box.From what I've read, it seems that many of the things that come standard on the Pico, such as protocol decoding, mask testing, etc., are add-ons that cost big bux from the traditional scope makers.

author: David Hess
author_rank: Super Contributor
timestamp: April 03, 2014, 06:05:41 pm
content: I wonder what the waveform acquisition rate is for the Picoscope 6000 series. The specifications are not very clear.

author: jpb
author_rank: Super Contributor
timestamp: April 03, 2014, 08:15:17 pm
content: Quote from: David Hess on April 03, 2014, 06:05:41 pmAs a USB scope it doesn't work quite the same way. It obviously can't display many waveforms per second as they have to be transferred via USB, but it does have a large amount of memory so it grabs a large chunk and then software can search for glitches.The PicoScope 6000C states that it can grab 10,000 waveforms in under 10 msecs at its peak so I guess that is about a million waveforms persecond. Quote below:Digital triggering also reduces re-arm delay and this, combinedwith the segmented memory, allows the triggering and capture ofevents that happen in rapid sequence. At the fastest timebase youcan use rapid triggering to collect 10,000 waveforms in under 10milliseconds. The mask limit testing function can then scan throughthese waveforms to highlight any failed waveforms for viewing inthe waveform buffer.This is perhaps not as convenient as say the Agilent continuously displaying at that rate but then it does have up to 2GB of memory in the top model.The reason I didn't go for the picoscope when I was looking was the less convenience, the fact that the sample rate drops as you use more channels (though it is still quite high) but perhaps mostly because the input voltage is rather limited compared to a traditional scope (though this probably isn't that important with x10 probes).

author: David Hess
author_rank: Super Contributor
timestamp: April 03, 2014, 09:43:25 pm
content: Quote from: jpb on April 03, 2014, 08:15:17 pmBut a USB oscilloscope could work this way. If waveforms are accumulated in the instrument and only the display updates are sent then the later does not affect the performance of the former. There is no conflict with having millions of waveform acquisitions per second even if the display is on the far side of the USB connection. Updating the display faster then the frame rate does not help anyway. DPO style oscilloscopes operate this way in some form or another in contrast to oscilloscopes that use segmented acquisition memories.Quote10,000 waveforms in 10 milliseconds matches the 1 microsecond rearm time of the trigger.What about over a period of 10 seconds? I am not usually looking for rare events within 10 millisecond time frames.Going by the streaming data rate, the waveform acquisition rate will be about 6000 per second across all channels.QuoteI am used to using short record lengths for maximum waveform acquisition rates anyway.QuoteYou could think of it as the sample rate getting better as you use fewer channels.

author: Neganur
author_rank: Unknown
timestamp: April 04, 2014, 03:16:29 pm
content: there is also the option to use one of the rack-versions of Agilent's scopes. I was thinking of something like this:http://www.ebay.de/itm/171081178220It's essentially an Agilent DSO6014, 4-Ch 100 MHz oscilloscope but without the display.

author: AndersAnd
author_rank: Frequent Contributor
timestamp: May 04, 2014, 10:31:36 am
content: Quote from: w2aew on April 03, 2014, 02:19:00 amAre PC scopes really cheaper though?When I bought a Rigol DS1052E 50 MHz scope some years ago I was also considering buying aPicoScopeUSB scope orTiePieUSB/Firewrire scope instead, but they actually all seemed more expensive for similar specifications. Even more so if you hack the Rigol to higher bandwidth.And there's still the possibility to connect a stand-alone DSOs to a PC for and control it from there and get a larger screen.On a related note, what's best bang for the buck?PicoScopescope,TiePieor a another PC-based scope?

author: echen1024
author_rank: Super Contributor
timestamp: May 04, 2014, 07:33:28 pm
content: For the $3K+ you would be spending on this scope, you might want to look at the new Tektronix MDO3000. They are now running a promotion with a free 3GHz spectrum analyzer, as well as a protocol decoder of your choice.

author: Galenbo
author_rank: Super Contributor
timestamp: May 04, 2014, 10:38:10 pm
content: Quote from: Sal Ammoniac on April 03, 2014, 05:55:36 amMaybe the best for you is to save money and buy the cheapest Rigol 50Mhz (for testing inputs, filtering, signal conditioning) but also buy a PC based logic analyser/protocol explorer/bus pirate.The reason for choosing pc-based here is the ease of data transfer to HD, integration with other software, better representation, more storage options,...Don't forget without a signal generator, possibilities are limited with a scope. You can make your own, or also buy a Rigol cheapass one (with amplifier/buffer) It works fine.