Low end logic analyser/scope - Page 1
Forum section: electronics / testgear

author: NickS
author_rank: Unknown
timestamp: October 23, 2013, 02:56:14 am
content: I'm looking for my Christmas present at the moment which needs to be cheap (sub $300) that will primarily be used to measure AVR kind of speed digital signals, and maybe check for bad ripple or some minor analog stuff as an optional.I'd ideally go for a nice DS1074Z but it didn't get wife approved.Dave reviewed the Saleae but you don't get an awful lot for $150.Then I came across the Bitscope BS10 (http://www.bitscope.com/product/BS10/) which is $245 but includes 2 analog channels, a basic sig gen and can read at double the digital speed of the Saleae.Basically all its specs are somewhat better than the Saleae from what I can see. The software looks better as well.Plus it is Aussie made so shipping is dirt cheap for me.I can't find much information about it from other sites however. There doesn't seem to be many reviews.Are there any other PC based logic analysers/scopes (Linux software prefered) that I should check out?If I get the Bitscope I might shoot it down to Dave so he can do a review/teardown/comparison vid. He isn't too far away.

author: dfmischler
author_rank: Frequent Contributor
timestamp: October 23, 2013, 12:46:35 pm
content: The problem with that BitScope model 10 is that it claims 100 MHz analog bandwidth, but it only samples the analog inputs at 20 MSa/s. So it might work OK on repetitive signals, but the fastest one-shot signal you can capture on that scope without aliasing might be a 10 MHz sine wave, or perhaps as much as a 4 MHz square wave. Also, where do you plug in the standard BNC oscilloscope probes? My conclusion is that it is a toy.

author: Unknown
author_rank: Unknown
timestamp: October 23, 2013, 01:11:05 pm
content: 20 MS/s is indeed lousy (the Rigol DS1052E varies between 250 MS/s and 1 GS/s, and even 250 MS/s is low for a 100 MHz scope), enough for about 2 MHz of real-time bandwidth (the only useful kind of bandwidth for many digital signals which you typically capture in one-shot mode). It looks like memory depth is only a few kpts, compared to 1 Mpts for the DS1052E and hundreds of Mpts for the Saleae.In general PC-based scopes suck compared to bench scopes for most applications. PC-based scopes that can do at least 500 MS/s with two channels,have a few hundred kpts of memory and a decent dynamic range (few mV/div to a few V/div), you're likely paying more than a low-end bench scopes with similar specs. How about just getting a DS1052E (or other sub-$300 scope like the Siglent, Hantek or Owon scopes) and saving for a LA later? Or the other way around. Two channels is usable for most serial buses, so you could probably get by without a LA. It's also good to start troubleshooting with a scope since it will also show analog problems that a LA would miss.

author: NickS
author_rank: Unknown
timestamp: October 24, 2013, 12:40:22 am
content: Haha yes the analog part of it is a toy, but I generally don't work with analog circuits so it is ok for my purposes.I did notice that the 100MHz is only going to ever work on a highly repetitive signal.It beats the Saleae and similar products though which don't have any analog capability.Check out the waveform that it captures from a 20mhz crystal starting up (towards the bottom).It actually looks surprisingly good given its capabilities. I won't be monitoring 20mhz signals anyway.No BNCs. 2 of the IO pins are analog inputs. More expensive models have BNCs.

author: rolycat
author_rank: Super Contributor
timestamp: October 24, 2013, 01:35:04 am
content: The Bitscope was a nice idea when it was created fifteen years ago, but it really hasn't moved with the times. The 1998 original could do 25MS/s with an ADC which was an old design even back then.That 20MHz waveform is mostly fiction.

author: Unknown
author_rank: Unknown
timestamp: October 24, 2013, 01:37:10 am
content: For the crystal startup they must have rigged the circuit to cycle the oscillator every 10 ms or so, since crystal startup is generally not a periodic signal. Expect the signal to be much worse (approximately one point per period) in any real-world circuit where you'd capture the signal in single shot mode. The frequency of the apparent (heavily aliased) signal would be the difference between the sampling rate and the crystal frequency, and could be as little as a few Hz if you're 'lucky'.Double check the memory depth, especially for the logic analyzer. USB streamers like the Saleae and Usbee generally have almost unlimited memory (hundreds of Ms). The Intronix LogicPort has only 2 kS, but has compression and better triggering to alleviate this problem. It looks like the memory depth of the Bitscope with 8 channels enabled is only 6 kS without compression and what looks like only basic triggering. This can be severely limiting, especially if you have a part that receives a command at a relatively high frequency, then waits a few ms or longer, and then responds. For exampe the full initialization sequence of a display. Or need to find a certain command in a long datastream. Sample compression can help with the former, advanced triggering (especially based on the address or contents of a packet) can help with the latter.If you've got your heart set on the Bitscope go right ahead, nobody here is going to stop you.

author: NickS
author_rank: Unknown
timestamp: October 24, 2013, 01:52:06 am
content: Quote from: alm on October 24, 2013, 01:37:10 amI'm not 100% convinced about the BitScope yet, I just haven't seen much else in the same price bracket.Looks like the LogicPort and the Usbee are both around $400 which for my purposes seems somewhat higher for not a massive amount of improvement in the specs.

author: Unknown
author_rank: Unknown
timestamp: October 24, 2013, 01:13:10 pm
content: My advice would be to not pay too much attention to the toy 'oscilloscope' in the Bitscope. You're probably barely going to use it once you get a real scope (even a 20 MHz analog scope would be superior for most applications).Some other alternatives in your price bracket:Asix Sigma2(has been discussed on this forum)ChronoVu LA-8 or LA-16Hantek 4032L(review)The various Zeroplus logic analyzers(have been repeatedly discussed on this forum, including hacks to get more memory on lower models)Most offer software that you can download and try without owning the hardware, this should give you some feel for UI and features.

author: R_G_B_
author_rank: Frequent Contributor
timestamp: October 24, 2013, 06:16:01 pm
content: In general PC-based scopes suck compared to bench scopes for most applications.Try telling that to companies like National Instrument's.It all depends on the application. Yes for asynchronous transfers high sampling is a must. For low frequency stuff that requires a high resolution such as low frequency data aquasition then a high speed scope proberbly won't do you much justice if your sampling low frequency weak signals. That's the compromise between high bandwith vs high resolution sampling.

author: Unknown
author_rank: Unknown
timestamp: October 24, 2013, 07:25:37 pm
content: Quote from: R_G_B_ on October 24, 2013, 06:16:01 pmNote the quote link in the top right corner of every post.Quote from: R_G_B_ on October 24, 2013, 06:16:01 pmFor years NI has been proclaiming the death of the stand-alone bench instruments and that they would be replaced by an NI mainframe with scope and DMM cards. Last time I checked even most engineers at NI had a standard Tek/Agilent scope and Agilent DMM on their bench. Also please name an NI instrument that can compete with the Rigol DS1052E on price/performance. Or the DS2072, or even the Agilent DSOX2002A. NI instruments are great for complex automated setups with a high degree of integration between the instruments. Not so much for an engineer making a wide range of measurements.Quote from: R_G_B_ on October 24, 2013, 06:16:01 pmFor low level signals you just need amplification, not more resolution. There are some applications where a higher vertical resolution is useful, which is why I wrote that bench scopes are better 'for most applications'. Note that the scope discussed in this thread only has 8 bits of vertical resolution. It only goes down to 10 mV/div, while most 'real' scopes go down to at least 5 mV/div, and sometimes 1 mV/div or 2 mV/div. So it has neither fast sample rate, nor high resolution, nor high sensitivity.

author: R_G_B_
author_rank: Frequent Contributor
timestamp: October 24, 2013, 08:48:04 pm
content: Yes your correct amplification is important for weak signal detection. More bits post amplification and detection allows you more detail on the display. This it also depends on the screens vertical resolution.As for NI, yes they create application interfaces for other manufacture.Things that you mention are as important than bandwidth alone. The analogue front end is a major factor and not just the sampling rate.

author: jmcdonald
author_rank: Contributor
timestamp: October 24, 2013, 11:09:03 pm
content: You went about it the wrong way you need to see if you can get approval for an Agilent MSOX2014A ($3000+) than when rejected ask adout the DS1074Z.

author: NickS
author_rank: Unknown
timestamp: October 24, 2013, 11:53:35 pm
content: Quote from: alm on October 24, 2013, 01:13:10 pmYeah I still aim for a real scope maybe in 12 months. I'm slightly interested to find out how much I use the toy scope.Thanks for that list. Quite a few other possibilities to think about now.

author: madshaman
author_rank: Frequent Contributor
timestamp: October 25, 2013, 05:18:04 am
content: I know "used" might be a faux-pas for a christmas present, but how about a used HP1650 or Tek1240 logic analyser?Then ask the wife to set aside budget to save up for that Rigol?If you want a "good" usb-based scope, you're going to pay for it :-(

author: madshaman
author_rank: Frequent Contributor
timestamp: October 25, 2013, 05:22:21 am
content: P.S. Even for digital, it's a good idea to have a scope with a significantly higher analog bandwidth than the signal speed you'll be working with. If you've got some kind of noise or high frequency oscillation on a data line or if the signal on the line is highly attenuated for some reason, the logic analyser won't be able to show you that.

author: Fsck
author_rank: Super Contributor
timestamp: October 25, 2013, 05:36:03 am
content: Quote from: madshaman on October 25, 2013, 05:18:04 ambut, that stigma doesn't apply to cars apparently. people really dig their classic carswe did electronics equipment so I don't understand why that exception wouldn't apply?

author: madshaman
author_rank: Frequent Contributor
timestamp: October 25, 2013, 07:19:40 am
content: Quote from: Fsck on October 25, 2013, 05:36:03 amOh, I totally agree! My honey said (half in jest, but half seriously) that if she gets her promotion at work, she'll buy me all the oscilloscopes I want. We'd probably rather send our future children to university, but maybe I'll set her homepage to this:http://savings.tm.agilent.com/index.cgi?ALIAS=MSO9104A&User:LANGUAGE=en;-)

author: jmcdonald
author_rank: Contributor
timestamp: October 27, 2013, 07:22:56 am
content: Quote from: madshaman on October 25, 2013, 07:19:40 amTell her it you pay for itself in no time