Help Choosing a Logic Analyzer? - Page 1
Forum section: electronics / beginners

author: clansd99
author_rank: Contributor
timestamp: May 20, 2023, 02:40:19 am
content: Hey folks,I'm looking to do some low-frequency (<1MHz) debugging of a 12 channel digital system (5V). I would like to use this as an opportunity to buy a logic analyzer. Any recommendations?Can I get away with something for $25? Or is it better to go $200-250? I am a student so keep in mind I can get student discounts.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 20, 2023, 03:49:47 am
content: the Kingst brand as good ones not costing a fortune ... but rise rapidly if you go on the high specsSaelae is a know one but huges prices ...and on Fleabay or Aliexpress you can find some for cheapIt depends of your voltages inputs tough, many offers added decoding in the software

author: barshatriplee
author_rank: Regular Contributor
timestamp: May 20, 2023, 04:46:47 am
content: Sparkfun's USB Logic Analyzer - 24MHz/8-Channel is good. But from your question, it looks like you need a 12-channel one.https://www.sparkfun.com/products/18627Here is a design of a 16-channel logic analyzer. You may consider making this too.https://www.pcbway.com/project/shareproject/16CH_Logic_Analyzer_de399909.html

author: EPAIII
author_rank: Super Contributor
timestamp: May 20, 2023, 05:01:54 am
content: Logic probes come in many shapes and capabilities from simple devices that can display a single circuit point as HI or LO and usually with an additional pulse light. I have a simple one that which I built a number of years ago. Or they can have multi-channels, again with just LEDs to display their state.You might look into the USB scopes. I have one, which is probably not the best, but which has two channels with 10 bit resolution and another 16 channels with single bit resolution. You can connect to a total of 18 points in a circuit and see two of them in great detail. And the software can provide a number of measurements on the two 10 bit channels. That can include things like decoding data streams. I also have a two channel digital scope which has great capabilities. But it does not have those 16 single bit channels so I can only see two circuit points at a time with it.Read the descriptions. Most will analyze digital signals. They are probably better than a simple logic probe. But perhaps just a bit more expensive while being at least only 25% of the cost of an entry level digital scope (which would also be a good choice). Of course, you do need a computer or pad to use them but you probably already have that.https://www.google.com/search?client=firefox-b-1-d&q=usb+oscilloscope+for+pc

author: tggzzz
author_rank: Super Contributor
timestamp: May 20, 2023, 05:21:08 am
content: Quote from: clansd99 on May 20, 2023, 02:40:19 amDepend on what type of debugging you need to do.In digital circuits the frequency is often a misleading metric; digital circuits specifications are in terms of timing. Thus violating setup and hold times is just as easy and problematic on a 1Hz signal as a 1MHz signal - the nanoseconds countIf you suspect intermittent "corruption", then you may need to assure signal integrity, i.e. that the setup and hold times and the voltages are within limits specified for the logic family. The voltages require an oscilloscope, the times require either a scope or a fast logic analyser.If you want to catch occasional problems, then you would benefit from having good arm/trigger/filter mechanisms. Those can be muchmuchmore powerful than anything available with a scope.If you are debugging a synchronous system, then you would benefit from being able to treat one signal as a clock, and only capture information on the rising edge. Being able to use another signal as a "chip select" will enable you to only capture information related to one device on a bus.If you want to see messages being passed, then a protocol analyser may be the instrument of choice.

author: golden_labels
author_rank: Super Contributor
timestamp: May 20, 2023, 05:33:45 am
content: Caveat emptor. Be aware, what are the limitations.A 24 MHz logic analyzer will be able to read signals at that rate, but signal timing will be completely off in the higher range. That will not affect timing between synchronized channels, but will miss differences between unsynchronized channels and timing accuracy will be limited to the maximum clock rate. For analyzing well-behaving logic this is enough, but any timing or signal integrity issues or spurious spikes will go unnoticed.Not a problem by itself, but buying your first logic analyzer you may be not aware of that limitation. Similar to how people buying their first scope may not be aware, that a 100 MHz scope will not let them see a nice 100 MHz square wave. Obvious, when you already know it, but not so clear before that.In the past I was usingOpen Bench Logic Sniffer, but no idea about the current state of the project. Their forum seems inactive.

author: EPAIII
author_rank: Super Contributor
timestamp: May 20, 2023, 07:02:56 am
content: To the contrary, many entry level digital scopes have most, if not all of the features you describe:Frequency: Even my USB scope has spectrum analyzer software. In a 45+ year working career I dreamed of having a spectrum analyzer. Now, with software, the algorithm seems to be out there and commonly known. Most, if not all digital scopes have it and it does not appear to increase the price.Timing: Of course timing is of great importance in digital circuits as well as having a great history of importance in analog ones. The key here is TRIGGERING. Scopes, all the way back to the first, tube type one I used 50 years ago, had triggering. Now, an entry level digital scope has triggering options beyond my wildest dreams. You just need to learn to use them. Trigger with one channel and observe the timing on the others. That's a simple sentence that glosses over decades of scope experience.Logic analyser: This can be a stand-alone instrument or some software in a probe or scope. But today it is software and fairly easy to include in any of them. Even most entry level digital scopes will have various forms. READ the specifications to see if any particular one has what you want/need.Treat one signal as a clock: This falls under triggering. You trigger from a "clock" and observe things in their time relation to that clock on other channels.Protocol analyser: Again, my entry level scope has this, but there are MANY, MANY protocols. As I said above, READ THE SPECS. to be sure you get the ones you want/need.Buying any electronic test equipment is an exercise in READING the SPECIFICATIONS. And they are available on line. If a piece of equipment does not have DETAILED, published specifications, then LOOK ELSEWHERE!On the practical side, entry level digital scopes (under $300 USD) will have most, if not all of the features that an undergraduate student will ever use. I am not familiar with the prices or exact features of current logic probes or analyzers so read the specs. (Oh, I said that before, didn't I?)Quote from: tggzzz on May 20, 2023, 05:21:08 am

author: tggzzz
author_rank: Super Contributor
timestamp: May 20, 2023, 10:07:53 am
content: Quote from: EPAIII on May 20, 2023, 07:02:56 amTrue but irrelevant to the point I made.You repeatedly make statements to the effect that a scope is sufficient. Not so for the OP's requirements and many others; my guess is the OP's system has an 8-bit data path plus up to 4 control signals. For that you would need a 12+channel scope! OTOH you are meaning a mixed signal scope then you should state that, because MSOs aren't entry level scopes.QuoteThat's fine for signal integrity issues, but insufficient for the complexsequencesthat occur in digitalsystems, especially where firmware is involved.QuoteFor many problems with digital systems (with assured signal integrity) the detailed timing isirrelevant noisethat obscures the problems. Often what you want is a simple list of values read/written to onespecificdevice, with their timing quantised in clock cycles (not ns). A logic analyser in state mode filters out that noise, presenting just the important signal in the form of alistof values.A decent logic analyser will also enable far more triggering and filtering, so that nothing is captured/stored/displayed until the one specificsequenceof events has occurred, and then only theinteresting subsetof information is stored and displayed.One easy-to-explain example of such filter+capture: I used an LA to capture the instruction sequence in a microprocessor-based system, thus enabling me to demonstrate a fault in a third party professional RTOS. Basically I showed that my code gave a value to the RTOS, but the RTOS returned a different value back to my code. Based on theshortevidence I produced, the vendor quickly fixed their bug. That would not have been practical with a scope.Many similar things frequently occur in digital systems where there are multiple cooperating subsystems, probably made by different companies.If you have only used cheap logic analysers, you won't have appreciated how much crap they can prevent you seeing.Once you get to the protocol analysis state, never underestimate the value of a printf() statement and/or keeping your own internal log of important information (especially sequences of events/states of an FSM).QuoteThat is easy to say and isnecessary, but in practice it isn'tsufficient.For a complex tool, such as an MSO or decent logic analyser, the datasheetcannotgive sufficient detail. You have to read the entire user manual. And you have to understand the significance and limitations. That's very difficult for a beginner - but a little easier for someone that has previously run into the limitations of a tool and become aware of what they really need.That is a good argument for trying something cheap and simple,plusbeing aware of general facilities offered by more capable tools.Quote

author: tatel
author_rank: Frequent Contributor
timestamp: May 20, 2023, 05:42:38 pm
content: Perhaps this would be good enough. There are now faster models with USB3. DSLogic Plus model in the attachment.https://www.dreamsourcelab.com/shop/logic-analyzer/dslogic-plus/Clones un peut partout, make sure you get one with coaxial fly wireshttps://es.aliexpress.com/w/wholesale-dslogic-plus-logic-analyzer-5-times.html

author: langwadt
author_rank: Super Contributor
timestamp: May 20, 2023, 05:51:37 pm
content: if you are on a budget this will do 16 channels,https://www.ebay.com/itm/373762362969I believe the IC is 5V tolerant

author: mwb1100
author_rank: Frequent Contributor
timestamp: May 20, 2023, 07:01:26 pm
content: These other videos by OpenTechLab are also worth watching, but keep in mind they're 5 years old:--The guy who did these OpenTechLab videos had significant involvement in the sigrok tools.

author: tggzzz
author_rank: Super Contributor
timestamp: May 20, 2023, 08:00:26 pm
content: Quote from: tatel on May 20, 2023, 05:42:38 pmThat's overkill; even my 64 channel 800MS/s Agilent 682AD uses flat "IDC" cable. Good quality and presumably with a specified impedance, but not coax.https://www.axiomtest.com/documents/models/Keysight%201680A%20Data%20Sheet.pdf

author: tatel
author_rank: Frequent Contributor
timestamp: May 20, 2023, 11:59:01 pm
content: Quote from: tggzzz on May 20, 2023, 08:00:26 pmNot going to get into any argument, but did you watch the video I linked? There is a comparison and, well, I would call it an improvement. YMMV.

author: tggzzz
author_rank: Super Contributor
timestamp: May 21, 2023, 09:21:14 pm
content: Quote from: tatel on May 20, 2023, 11:59:01 pmI very rarely watch videos because the information transfer rate is usually too poor: I can speed read 10* faster than people talk. My remaining life is too short.I will watch a video that (1) needs moving pictures and (2) I have strong reason to believe I will learn something and (3) I can skip the useless crap and go straight the useful bits.That filters out 99.99% of YouTube vids.Now, in what way as the moving pictures in that vid more beneficial to me than still images?

author: tatel
author_rank: Frequent Contributor
timestamp: May 22, 2023, 12:02:16 am
content: Quote from: tggzzz on May 21, 2023, 09:21:14 pmIDK & IDRC. All I know is, if you can't be bothered, there's no point in going further, don't you think so?That said, about 25:00 that video shows a 100 MHz square signal, LA connected to DUT, first with coax wires, then with normal wires: signal is really worse the later case. There's like a 3x difference in amplitude. One would think decoding errors would be more likely with a so distorted signal.Of course the guy says "200 MHz",which is impossible with an entry-level Rigol. Moreover it can be seen "100 MHz" on the screen. Maybe he's speaking about sample rate?Comparison is made at equal conditions anyway. Both DSLogic models can go up to 400 MHz when using 4 channels, so I thought the sensible option was to get the one with coax fly wires. It also has more memory. I got a clone from Ali: €75. I don't think it's overkill.For more static details, please seehttps://www.eevblog.com/forum/testgear/recommended-cheap-logic-analyzer-for-37mhz-frame-sync-spi-buses-(16ch)/msg3588526/#msg3588526

author: MathWizard
author_rank: Super Contributor
timestamp: May 22, 2023, 06:27:56 am
content: I want to get something like the Hantek 4032L PC USB Logic Analyzer 2Gbit Memory Depth 150MHz Bandwidth 32Channels 400MSa/s Sampling Ratehttp://hantek.com/products/detail/14I can do a bit of LAing on my oscilloscope, it might even have a LA add-on. The Hantek is ~170US on amazon anyways.I'd spend that much for a PC based LA. IDK how fleshed out the software is. I think the next level LA's are 400-600USD.I was wondering how suitable a VGA or DVI cable is for making some LA probes?

author: pdenisowski
author_rank: Super Contributor
timestamp: May 22, 2023, 10:49:55 am
content: Quote from: tggzzz on May 21, 2023, 09:21:14 pmExactly this. Even when I find videos that meet those 3 criteria, I watch them at 2X

author: tggzzz
author_rank: Super Contributor
timestamp: May 22, 2023, 11:59:05 am
content: Quote from: tatel on May 22, 2023, 12:02:16 amOK, that cut 45mins of my time (i.e. >> "30s elevator pitch") down to a couple of minutes.Firstly that couple of minutes was "talking head" and could have been better presented as a picture plus text. That reinforces why I rarely bother with videos. Better presentation would have meant more work on behalf of the talking head and wouldn't have been so much of an ego-boost. I prefer authors that think of their audience first and themselves second.Secondly i always have problems with someone using sine wave measurement/characterisation for digital signals. The relevant tests are logic waveforms and looking at the risetime (and eye diagram if relevant). I'll bet if he has changed the sine wave frequency slightly the scope would display completely different results - probably including "amplification" at some frequencies. Note that the waveforms seen by the probewon'tbe those seen by the LA input - basic transmission line theory.Thirdly, the video doesn't show any "coax wires". It does appear to show signal-ground pairs (i.e. a narrow ribbon cable) presumably with a hidden RC network equivalent to a *10 scope probe. See the attachments for the HP medium speed LAs.Note my statement that started this sub-thread...Quote from: tggzzz on May 20, 2023, 08:00:26 pmSummary:all probes become part of the UUT. Poor probing techniques lead to poor resultsa controlled impedance doesn't require coax. Ribbon cables are usually sufficient.

author: pdenisowski
author_rank: Super Contributor
timestamp: May 22, 2023, 01:59:18 pm
content: Quote from: tggzzz on May 22, 2023, 11:59:05 amWe (R&S) use ribbon-style cables to connect to logic pods on all of our oscilloscopes.(Edit: one on the left is the "new" style and one on the right is the "older" style)

author: rstofer
author_rank: Super Contributor
timestamp: May 22, 2023, 02:37:18 pm
content: I would also look for LAs with a 'state clock' input. Rather than use the unsynchronized internal LA clock to sample, the external 'state clock' synchronizes the LA with the logic. This is useful for things like state machines where you know when signals change because the 'state clock' takes the sample at the instant it changes state.Search for 'state mode' here:https://articles.saleae.com/logic-analyzers/how-to-use-a-logic-analyzerSometimes you have to give up an input channel so you don't wind up with 16 channels, just 15 plus a clock input (which might have been the 16th input anyway).

author: rstofer
author_rank: Super Contributor
timestamp: May 22, 2023, 02:58:19 pm
content: I like either the Digilent Analog Discovery 2 or, more to the point, the Digital Discovery.QuoteIt's 5V tolerant on inputs but outputs just 3.3V (or 1.8V) but 3.3V may be adequate for most 5V logic inputs. Yes, it is also a pattern generator for driving project inputs.It has UART, SPI, I2C and CAN bus protocol analyzers in the Waveforms software which you can download and play with using a 'Demo' device without having to spend anything.Check out the Reference Manual linked on this page:https://digilent.com/reference/test-and-measurement/digital-discovery/start

author: tatel
author_rank: Frequent Contributor
timestamp: May 22, 2023, 07:03:56 pm
content: Quote from: tggzzz on May 22, 2023, 11:59:05 amNot really sure what are you speaking about, but, hey, I'm not a native enplish speaker. So I'm missing some reasoning perhaps... Anyway:1) We are talking about these coax wires used on DSLogic Plus, which is the LA I suggested. Please see attachment. DSlogic Basic, wich seems to be unavailable now, used fly wires more like DuPont wires. What I said was about making sure that, should a DSLogic model be purchased, better to have the model with coax wires. Don't know about old boat anchors; just that they would have hardware triggers.2) Not seeing the video makes you miss quite a bunch of context. That makes quite difficult to have a common understanding and makes any comunication effort almost improductive. Of course nothing compels you to loose your valuable time, but I have to remember you this is a beginners thread and, being here, will always by definition make you waste your time. In this case, we are all wasting our time here it seems.3) I'm not sure what you mean with "talking head". I can't see any guy appearing on screen. Video shows a teardown of the device. Speaks about stream and buffer operation.Shows the input front end ofthisdevice we are speaking about, including protection. Compares it with the previous Basic model, which does have RC networks at the input, absent in the Plus model. Explains how this could induce ringing and applies a reactive load to the DUT and why getting rid of these RC networks seems to be a good idea to him. At the 11:12 mark probing arrangement can be seen, with coax fly wires that doesn't look at all like any IDC cable I could know about. Then a tipycal Salaeaeaeae clone is shown. It doesn't have any IDC cable either. Just a bunch of DuPont wires. Explains how these are in some way inductors and will probably distort the signal in some way. Says how using coax for most of the fly-wire should reduce the size of any inductive loop, which would get worse the higher the frequency goes. So response will be flatter at any frequencies. But there are also some downsides so he shows how DSLogic Plus tries to cope with it. Not optimally, it turns out. So to explain it in more detail a simulation is shown. Then a experiment (we will have a closer look at that experiment later) Then he speaks about the DS-sigrok drama, which is something some of us care about. Then DSWiew shoftware can be seen in action and he explains why, even after giving due credit, to integrate it into sigrok is not an easy task. Last, he explains why even him, being the guy that worked on the ripped-by-DS Pulseview sigrok app, likes the device and thinks it's great. I claim this is a really good educative video and that any newbie looking into LAs will probably find the time watching it well worth, not wasted.4) Now that I --due to you being too near to death-- wasted my time --which is as valuable as yours-- in a comunication effort, now I have to ask you to try and be of any help, which you so far don't have been so much on this thread. I'm pretty sure OP will get more knowledge watching that video than listening anything you said so far. I for one can really say that's the case. I do it respectfully, and asking you to be respectful too.5) The guy isn't measuring any sine wave, but a 200 MHz square one. I guess it's some of that missed context, but I mentioned it by writing. Didn't you noticed it?6) About probing techniques, I don't know he could have done it any better, and I would be really interested in learn something about it. I can be bothered to read anything, but I often find videosareuseful7) About ribbon cablens being good enough, that's not the point. Point is, coax is better than DuPont fly wires. OTOH, if coax is better than even ribbon cable, and can be in a €115 device, why not?

author: tatel
author_rank: Frequent Contributor
timestamp: May 22, 2023, 07:28:52 pm
content: Quote from: rstofer on May 22, 2023, 02:37:18 pmDSLogic devices have it.Of course there will be other devices better than these chinese things, but when I look at the prices, I run tail between legs. I find DSlogic can't be beaten for the price, and can't justify going to dearer machines. OTOH, a friend of mine got one of these €8 Saleae clones so often recommend, and it doesn't work. It's crap. So, pretty happy with what I got. I could only ask for it being fully integrated into S¡grok-Pulseview

author: tggzzz
author_rank: Super Contributor
timestamp: May 22, 2023, 08:21:31 pm
content: Quote from: tatel on May 22, 2023, 07:03:56 pmA bunch of points...The video shows a 200MHz sine wave. I didn't spot that he was feeding it with a square wave, because I would never have thought of looking at a 200MHz square wave with a 200MHz(?) scope. A PRBS plus eye diagram would reveal problems that occur at the range of frequencies in arbitrary/typical digital signals."Talking head" is shorthand for a TV programme (etc) that has a monologue with no moving visuals that emphasise the speech. Usually it shows the presenter's mouth moving and arms waving, and no other information. In the youtube video's case the only moving thing was the cursor. That information could have been put across faster in words plus still pictures (possible annotated).I do find some videos useful, those that show things that cannot adequately be expressed in words and still images. Excellent examples are the (old) Pace videos that show soldering techniques including how the soldermovescorrectly and incorrectly. In general the USP of videos is showing how things change over time. If there is no change over time, they lose their unique advantage.In a private conversation MarkL has demonstrated that thespecificLA I mentioned does use coax - unlike the R&S LA mentioned by pdenisowski. MarkL has found the part numbers of the cable and other information not previously available to me. More embarassingly he has pointed out that if I "count the bumps" on the "ribbon cable", there are too few bumps for it to be ribbon cable with alternating signal-ground connections. I should have done that. Mea culpabut it is pleasing to learn something.Thus my position isnowthat ribbon cable is sufficient for signals up to a few hundred MB/s, but beyond that coax has advantages.We both agree that Dupont cables are simply not good enough. Having said that,shortones are used in the HP/Agilent diagrams I showed, between the encapsulated RC network and the gripper/gnd.Overall I hope the OP picks up that probing techniques are vital with signal containing RF energy - and that the system clock rate is irrelevant; what matters is the transition time. That, to me, is the really important point.

author: tatel
author_rank: Frequent Contributor
timestamp: May 22, 2023, 09:26:41 pm
content: Quote from: tggzzz on May 22, 2023, 08:21:31 pmI can agree also on that. But got bad news: young people seems to think reading is anachronic? Last week I encountered a long time unseen old friend of mine that was with his youngest kid, a girl perhaps 10-12 years old. I was presented to that girl with this statement: "Look, Nerea, did you said nobody reads? This guy is able to read 800 words/minute". The girl looked at me like if I was one of these invaders from Mars H.G. Wells wrote about.So I'm afraid we are on dinosaurs path.I didn't asked what's wrong with the girl.Best regards

author: tggzzz
author_rank: Super Contributor
timestamp: May 22, 2023, 09:51:40 pm
content: Quote from: tatel on May 22, 2023, 09:26:41 pmYesKurt Vonnegut's "Harrison Bergeron" springs to mind. Widely available online, there's no need to read more than the first page or so.

author: robca
author_rank: Frequent Contributor
timestamp: May 22, 2023, 10:52:12 pm
content: One more vote for the DSLogic analyzer. Really good software based on Sigrok (they had problems at the beginning trying to hide the origin), plenty of protocol decoders (even more than Sigrok).I have a U2basic which I upgraded to Plus changing the RAM and the device ID (https://www.eevblog.com/forum/testgear/upgrading-dslogic-basic-to-plus-without-eeprom-modification/). Unless you are comfortable with SMD soldering, I would not attempt the upgrade, though. The Plus costs as much a Basic+separate fly wires, so it's a better deal these days (was more than twice as expensive when I did my upgrade)The U2basic does everything the OP asked for and more for ~$70. The Plus is better but I rarely need to go above what a U2basic would do. The shielded fly wires are better than the basic ones, but only meaningful at vey high frequencies (and DSLab sells the shielded fly wire as an upgrade)I would not buy a standalone Logic Analyzer or a scope with LA functionality these days. When you are doing analysis on logic signals, having a computer that can visualize on a bigger screen and save files easily it's a plu. Also, Sigrok and the DSLabs software can use stacked protocol decoders that allow to decode, for example, an SPI EEPROM directly, extracting the data (vs capturing the SPI traffic and then looking the EEPROM commands to extract the data)

author: tggzzz
author_rank: Super Contributor
timestamp: May 23, 2023, 12:00:07 am
content: Quote from: robca on May 22, 2023, 10:52:12 pmThose are interesting and useful concepts.Personally I have found it is usually possible to use advanced arm/trigger/filter/capture configurations to usefully reduce the amount of information I have to look at. Where only simpler.config are available, it may or may not be possible to have deeper capture buffers and then post-process the buffers.Once you have to look at a lot of information, it is often more comfortable looking at it on a standard computer.