Which logic analyzer for beginners? - Page 1
Forum section: electronics / beginners

author: Watth
author_rank: Frequent Contributor
timestamp: February 10, 2022, 03:32:45 pm
content: Hey EEVPeople,As I'm starting to implement serial communications (I2C and SPI), I'm thinking of buying an entry level USB logic analyzer. 8 ports should be more than enough for me.I've seen on Aliexpress and Amazon that prices start in a range from 10 to 20 € for what seem to be a generic design. I guess it relies on free softwares, open source for some. I've seen that Sparkfun offers its own branded version.For a little more money, I've seen the BITMAGIC-BASIC-V1, but as far as I know, it doesn't provide better features.After that, prices go higher with features I don't think I need.Do these entry level perform adequatly for hobbyist's use? Are there brands to recommand?Thanks for reading this message!

author: daveho
author_rank: Newbie
timestamp: February 10, 2022, 04:28:00 pm
content: The cheap Saleae Logic clones (which I assume is what you're seeing based on the price range you mentioned) work quite well with Sigrok. For the price it's pretty hard to go wrong.

author: isometrik
author_rank: Regular Contributor
timestamp: February 10, 2022, 04:40:57 pm
content: I have used a cheap Saleae Logic clone at some point, but quickly found out they are very limited (no voltage level adjustment, limited sampling rate, etc).I ended up buying a DSLogic Plus from DreamSourceLab, and although it's more expensive than what you have budgetted, it's a more serious tool. Seehttps://www.dreamsourcelab.com/product/dslogic-series/for more details.The original Saleae Logic 8, Logic 8 Pro, etc. would also offer better characteristics, at a higher price however. Seehttps://www.saleae.comfor more details.

author: fourfathom
author_rank: Super Contributor
timestamp: February 10, 2022, 06:05:23 pm
content: I've also used the $12 Saleae clone with Sigrok, and it works fine for reasonably slow logic and standard logic levels (I assume, I've only used it for 3.3V logic). But I eventually wanted to use it on 100 MHz-clocked logic (FPGA) and somewhere above 10 MHz it just couldn't cut it anymore. So I spent a lot more money and got a DSLogic Pro16 (more than I needed, but that's OK with me). This definitely does the job. The DSLogic analyzer comes with "DSView" which appears to be based on Sigrok.

author: eugene
author_rank: Frequent Contributor
timestamp: February 10, 2022, 08:14:27 pm
content: If you happen to have a Raspberry Pi, you can use it as a logic analyzer withpiscope. The output is displayed on a pc (Windows or linux) via X11.notes:It's limited to 3.3V logic. If you're using 5V logic then your RPI will likely be destroyed.You need to install piscope and pigpio on the RPI.You need to install putty and ming if using a Windows machine for display.I don't know for sure what the sample rate is, but pigpio defaults to 200kHz, so I would guess that piscope does as well. That limits usable bandwidth to around 50kHz or so.If you don't already have a RPI, forget about buying a new one. Supply chain issues have made them impossible to find

author: rstofer
author_rank: Super Contributor
timestamp: February 11, 2022, 03:47:48 am
content: I think the upper limit is 400k bps for I2C so any LA that will sample at 4+ MHz should be adequate.I'm not sure what the fastest SPI link runs at but 60 MHz wouldn't surprise me. Any LA that can sample at 1 GHz would be adequate.In other words, don't run SPI at full speed and plan to probe it with a $10 LA. The thing is, not many people even try to run it that fast so it's up to the user how much they want to spend of going fast.The inexpensive LAs are a place to start. Get one and learn to work with it. I built the Sump.org LA from a Digilent Spartan 3 Starter Board and it samples at 200 MHz - pretty decent but I was running the FPGA project board at 50 MHz. Not ideal but it worked ok.https://www.sump.org/projects/analyzer/In terms of FPGAs, the Xilinx Vivado tool includes the capability of defining an Internal Logic Analyzer that runs in the same hardware at the same synchronous clock. This is on the hardware, not simply a simulation. Debugging FPGAs take a lot more creativity to find logic design errors.For a CPU, implement single-stepping either by instruction cycle (fetch through execute) or by state clock, preferably both. Also implement an address breakpoint that stops the state machine when there is an attempt to access a particular location in RAM. This will let you debug at the source code level, instruction by instruction after you hit the breakpoint.Before Vivado, I threaded a 32 bit debug bus through all of the components. It was commented out in all but the component under test. I needed a way to get signals generated 3 or 4 layers deep out to the pins.

author: Watth
author_rank: Frequent Contributor
timestamp: February 11, 2022, 11:06:47 am
content: Quote from: rstofer on February 11, 2022, 03:47:48 amI've seen I2C has modes up to 5 MHz with these new fangled FastModePlusProMega™. But I don't plan on using a LA in such fast modes. As for me it's about testing signal from sources I design (and not on existing equipment), I could simply adapt the serial speed a bit slower if needed. Same for SPI.Some repliers mentioned logic level issues, but I don't think I'll deal with anything other than 3 ~5.5 V. Silly question: if voltage is too high, wouldn't a resistor bridger do the trick?From what I gathered, this type of cheapo LA is a good start anyway; and it's totally worth the money even if one decides to upgrade later for a more sophisticated and pricey piece of equipment later.

author: rpiloverbd
author_rank: Regular Contributor
timestamp: February 11, 2022, 01:04:10 pm
content: I think Sparkfun's USB Logic Analyzer - 24MHz/8-Channel is a good choice for beginners. The price is also reasonable.https://www.sparkfun.com/products/18627

author: rstofer
author_rank: Super Contributor
timestamp: February 11, 2022, 03:25:28 pm
content: Quote from: Watth on February 11, 2022, 11:06:47 amIn theory but I haven't tried it;QuoteI have a couple of ways of cabling up a LA (my sump.org FPGA based, Analog Discovery 2, Digital Discovery) but I still bought one of the cheapos just to play with the software. It seems to work well. I'm a little fuzzy at the moment, I don't know if these cheapos have a state clock input. Having access to the internal clock of the device under test helps synchronize the samples.

author: tooki
author_rank: Super Contributor
timestamp: February 12, 2022, 10:40:24 am
content: Quote from: daveho on February 10, 2022, 04:28:00 pmAnd they also work with the Saleae Logic software, which is very easy to use, making it a great introductory logic analyzer system.

author: BBBbbb
author_rank: Unknown
timestamp: February 12, 2022, 11:09:21 am
content: Quote from: tooki on February 12, 2022, 10:40:24 amDo they still? With the 2.xx versions?2.xx is being actively improved and is a significant upgrade to the 1.xx versions, but I'm not sure those clones can still be made to work with the new SW,But Sigrok is quite OK even if the clones cannot work with Saleae.DSLogic seems (on paper) to offer even better performance than Saleae (in the price range), but I don't know anyone who could give me first hand comparison in reality, and DSLogic have been quite an assholes regarding SW development (actually breaking the Sigrok's FOSS license) so that is putting me off a bit from them.

author: Watth
author_rank: Frequent Contributor
timestamp: February 12, 2022, 12:25:32 pm
content: Quote from: tooki on February 12, 2022, 10:40:24 amThe Saleae website only features 400+ € devices. I there was a basic LA on which the clones are based, it's not there anymore.

author: Gyro
author_rank: Super Contributor
timestamp: February 12, 2022, 12:58:58 pm
content: They were the logic analysers that Saleae started the company with. They were basically the EzUSB application circuit with some input protection diodes and an expensive milled Aluminium case. They are still supported by their S/W (or at least were until recently - I don't know). All versions are on their website anyway. After Version 1.1.18, they did a partial rewrite and went to a lower contrast UI. It then took them a few releases to get the bugs out. In later versions still, they slowly added support for their newer analogue / digital models.EDIT...https://youtu.be/7OCPWCdg2ys

author: tooki
author_rank: Super Contributor
timestamp: February 12, 2022, 10:57:59 pm
content: Quote from: BBBbbb on February 12, 2022, 11:09:21 amAt minimum, the clones of the very first Saleae (the digital-only one) do. I have one of those.Some clones with analog claim to be supported too but I can’t vouch for that.Quote from: Watth on February 12, 2022, 12:25:32 pmCorrect, the clones are of discontinued models.