Author Topic: Cheaper Logic Analyzers  (Read 4839 times)

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Offline bobdabiulder

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Cheaper Logic Analyzers
« on: March 17, 2018, 10:51:37 pm »
Hi!  I was watching some OpenTechLab videos recently (please check out his channel, it's somewhere between Julien Illet and EEVBlog in terms of quality).  OTL knows a lot about these analyzers, and he effectively demonstrated a $6 LA in use.  I will probably get one of those SUPER cheap analyzers as a starter, but I also want a slightly better one.  I am looking at the DSLogic lineup.  Quick questions: Is the Pro or Plus model newer?  And, is the newest DSLogic the ONLY one to have USB-C & 256mb of RAM (for buffering)?  Also, what other similar LAs would you recommend for <$150USD?  Thanks!
 

Offline Stray Electron

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Re: Cheaper Logic Analyzers
« Reply #1 on: March 17, 2018, 11:28:33 pm »
  I see that you're in the US.  I don't know why you would even consider one of those TOY analyzers when E-bay is full of good high quality LAs from companies like Hewlett Packard.  I tried to sell an extra HP 1670D that I had a couple of years ago for $100 and no one even looked at it. This LA was like new and had all of the original manuals and paper work, grabbers, special socket adapters and was used less than one year. If you're smart you'll buy a good instrument like HP and it will serve you well for the next 20 or 30 years. Shipping can be expensive so if you're really smart you'll look for one in your area and drive over and pick it up in person. Not only will it save you money but you can be sure that it works and that everything is there.
 

Offline bobdabiulder

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Re: Cheaper Logic Analyzers
« Reply #2 on: March 17, 2018, 11:54:46 pm »
Thanks for the reply!  Good luck finding an LA in Wisconsin...  Anyway, I think i'd rather have one of these "toys" just for their simplicity, even if they will never compare to a quality HP LA.  And besides, I don't have that kind of bench space ;)
 

Offline TK

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Re: Cheaper Logic Analyzers
« Reply #3 on: March 17, 2018, 11:57:00 pm »
If you need to decode different protocols, Zeroplus LAP-C 16032 for around $150 is a good option.  It can decode over 100+ protocols.  16 channels, 32K per channel, 100MHz sample rate.
 

Offline nctnico

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Re: Cheaper Logic Analyzers
« Reply #4 on: March 17, 2018, 11:57:20 pm »
  I see that you're in the US.  I don't know why you would even consider one of those TOY analyzers when E-bay is full of good high quality LAs from companies like Hewlett Packard.  I tried to sell an extra HP 1670D that I had a couple of years ago for $100 and no one even looked at it. This LA was like new and had all of the original manuals and paper work, grabbers, special socket adapters and was used less than one year. If you're smart you'll buy a good instrument like HP and it will serve you well for the next 20 or 30 years. Shipping can be expensive so if you're really smart you'll look for one in your area and drive over and pick it up in person. Not only will it save you money but you can be sure that it works and that everything is there.
I don't agree with this for several reasons. Older doesn't mean more reliable. Older means big case, parts which run hot and fans which make noise.
Also the 'older' logic analysers are made for entirely different problems compared to the current digital circuits. Back in the old days you'd have a board filled with chips. Nowadays you have busses like DDR, PCIexpress, USB, I2C and SPI running between chips on a board. There is not much logic analysis needed for that. What is needed is stuff like protocol decoding and that is typically missing.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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Offline bobdabiulder

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Re: Cheaper Logic Analyzers
« Reply #5 on: March 18, 2018, 12:10:51 am »
I don't agree with this for several reasons. Older doesn't mean more reliable. Older means big case, parts which run hot and fans which make noise.
Also the 'older' logic analysers are made for entirely different problems compared to the current digital circuits. Back in the old days you'd have a board filled with chips. Nowadays you have busses like DDR, PCIexpress, USB, I2C and SPI running between chips on a board. There is not much logic analysis needed for that. What is needed is stuff like protocol decoding and that is typically missing.

Thanks for that help.  I agree, not having a usb interface is NOT a feature thanks to all these new protocols, etc.  Also, older can mean more reliable, just not *always* more reliable.  Old things can be cheaply made and therefore less reliable, just like any "new" thing.
 

Offline CustomEngineerer

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Re: Cheaper Logic Analyzers
« Reply #6 on: March 18, 2018, 02:34:05 pm »
The DSLogic Plus is the newer model. If you order the pro model directly from dreamsourcelabs, they don't even list a plus model on their site (just really out of date info on their site), you will receive the newer plus model, with the USB-C and coax leads. Can't believe they can't be bothered to update the info on their site, I'm sure the uncertainty of what you will receive drives a lot of people to just order from ebay instead of through them.
 

Offline rhb

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Re: Cheaper Logic Analyzers
« Reply #7 on: March 18, 2018, 03:29:21 pm »
Make sure you look at the voltage limits on the inputs.  The Digilent Discovery allows thresholds from 1.8 to 3.3 V, but *is* 5 V tolerant.  The inputs are straight to the FPGA.   The probes for my Instek MSO-2204EA have ADCMP561 comparators, adjustable trigger levels and are 40 V tolerant.
 

Offline bobdabiulder

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Re: Cheaper Logic Analyzers
« Reply #8 on: March 19, 2018, 01:04:24 pm »
The DSLogic Plus is the newer model. If you order the pro model directly from dreamsourcelabs, they don't even list a plus model on their site (just really out of date info on their site), you will receive the newer plus model, with the USB-C and coax leads. Can't believe they can't be bothered to update the info on their site, I'm sure the uncertainty of what you will receive drives a lot of people to just order from ebay instead of through them.

Thanks!  I’ll probably order it off of their website, since other people agree with you.  It is definitely odd that they don’t update their website!!
 

Offline kony

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Re: Cheaper Logic Analyzers
« Reply #9 on: March 19, 2018, 01:20:23 pm »
http://www.asix.net/dbg.htm
Is supported even in Sigrok, 512Mb buffer w/ HW compression, stackable.
 

Offline plazma

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Re: Cheaper Logic Analyzers
« Reply #10 on: March 19, 2018, 01:36:59 pm »


  I see that you're in the US.  I don't know why you would even consider one of those TOY analyzers when E-bay is full of good high quality LAs from companies like Hewlett Packard....

My work place discarded some HP LAs. No one wanted them. I saved the cables and grabbers. They are big and bulky and not good for modern embedded work.

I use a Saleae Logic16 clone. It works as specified and also works in Sigrok. Good unit for 30$.
 

Offline Bob Sava

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Re: Cheaper Logic Analyzers
« Reply #11 on: March 19, 2018, 01:41:35 pm »
Maybe it's obvious, but anyway, if you want inexpensive logic analyser you should start with Sigrok's supported hardware page:

https://sigrok.org/wiki/Supported_hardware#Logic_analyzers

Note about DSLogic  - there are a lot of different variants floating around (some with not very robust leads/connectors)  so the best is to get one directly from the manufacturer if you decide to get one.
 

Offline GigaJoe

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Offline free_electron

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Re: Cheaper Logic Analyzers
« Reply #13 on: March 21, 2018, 05:28:04 pm »
DDR, PCIexpress, USB, I2C and SPI running between chips on a board. There is not much logic analysis needed for that. What is needed is stuff like protocol decoding and that is typically missing.
apart from i2c and some spi you have NO chance of even sniffing the others. Those low cost usb bitstreamers
- don't have the bandwidth ( even a fast SPI bus is out of range for these streamers. try a 20MHz SPI ... or a 40 MHZ spi or QSPI... like an SD card . fat chance...)
- input level range ( modern busses use diff signals with very low swings and levels. these streamers are 5 or 4 volt ( if you are lucky) )
- load the bus ( a couple of picofarads extra on a pci-x bus and you inject errors.... )

and for real analysis
- they can't do eye patterns ( you need analog sampling for that)
- they can't do timing ( nowhere near fast enough )
- they can't do jitter
I know, some people will say : oscilloscope .. but the real logic analysers like a 16900 series board can digitize that ! They have that on-board.

so yeah. you can sniff an i2c bitstream. and some low speed spi.. ( try sniffing a 80Mhz qspi with those streamers .... )

But you are right : the packet decoding is also missing !

Get a Saleae 4 or 8 bitter.

Or a used 167xx or 169xx with a couple of fast boards if you must do REAL analysis on ddr, usb , and the faster beasts. ( 99.99 % of people don't do real analysis. they just sniff bits in a hobby project using an arduino. For that you don't need these machines)
« Last Edit: March 21, 2018, 07:29:44 pm by free_electron »
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Offline GigaJoe

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Re: Cheaper Logic Analyzers
« Reply #14 on: March 21, 2018, 05:58:55 pm »
I think, my clone 100M (samples) - 1 channel; 40M - 3 channels. It has some small buffer, so depend on timeframe capture the speed can be faster,  but honestly I never did any faster then 1Mbit ...

 

Offline carl0s

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Re: Cheaper Logic Analyzers
« Reply #15 on: April 26, 2018, 10:48:01 pm »
I just picked up a DSLogic Plus from eBay in the UK. I made sure I was paying £86 instead of £56. The £56 ones don't have the 256MBit buffer as far as I can tell.

It think it's OK.

Couple of things: Need 100MHz bandwidth to properly sample a 32MHz SPI bus. Need 50MHz to sample 16MHz SPI, otherwise just get garbage.

I think the Basic one, can't do >50MHz with more than 3 channels, because it can only do Stream mode as it has no buffer, however for SPI you could leave off MISO or EN/SS or something depending on what you're doing.

Other thing, and this is something the $999 Saleae can't do. Trigger on serial packet. Again, it needs to be in buffer mode as it's done on the FPGA (so the Basic edition is out), but the DSLogic Plus will trigger on up to 16 bits of serial data, like this:



The DSLogic, despite using a USB type-C connector, is only USB2 though. That may explain the limited bandwidth when not using Buffer mode of the Plus version. So in summary, get the Plus version with buffer. Thanks to a third party contributor, RLE compression has increased the storage capacity of the onboard memory greatly. DSLogic themselves don't seem to have done much work on the kit in the last few years, and you can't even register to their forums without emailing them with your transaction ID to get a code. No wonder it appears dead on there.

I'm quite happy so far I think. It came with the coaxial leads as well, in the separate bundles of 4 each. Again I think the cheaper Basic version doesn't come with those nicer leads. I had to connect up a few more grounds to get a good signal, but then my setup is pretty rough.

« Last Edit: April 26, 2018, 11:03:38 pm by carl0s »
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Offline mos6502

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Re: Cheaper Logic Analyzers
« Reply #16 on: April 26, 2018, 11:35:44 pm »
Is that one of them antistatic carpets?
for(;;);
 

Offline carl0s

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Re: Cheaper Logic Analyzers
« Reply #17 on: April 26, 2018, 11:43:24 pm »
Is that one of them antistatic carpets?

:D :D :D
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