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Thread: About buying a (not too expensive) logic analyzer

  1. #1
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    About buying a (not too expensive) logic analyzer

    As a hobbyist (and an electronic noob) I'm wondering if having a logic analyzer would help me to better understand digital/analog signals and identify problems

    I don't want to spend too much money as I'm not a pro, and found these analyzers from a French company (could be better for customer service, as this is the country I live in)
    https://www.ikalogic.com/pages/logic...ator-sq-series

    The SQ50 is around 100$ (89), what do you think about this model ?

    And another question : are the standard probes provided with any logic analyzer "compatible" with breadboards hole format ?

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    The SQ50 seems fine. Of course a logic analyzer is useless without a good companion software. Theirs is open source which is a plus, but I would still try it in demo mode (all l.a. softwares I know of have a demo mode with sample data), to see if you like it.

    I have two cheap l.a., which are more or less SalaeLogic clones; they fit my purposes quite well. Very useful to learn, debug stuff, reverse-engineering etc. Both have breadboard-compatible cables.

  3. #3
    Senior Member+ KurtE's Avatar
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    Depending on what it is you wish to do, having a Logic Analyzer can help a lot in understanding things and debugging stuff.

    I too am a hobbyist, and I personally own a couple of the Saleae logic analyzers and they have helped me a lot, and I use them for lots of different thing, like trying to understand exactly what Serial data I am generating and/or receiving, likewise for several other different protocols. I also use it to help debug other things, like I might use one or more unused IO pins, to help debug some code. I sprinkle in some digitalWrites into key areas of code and I can then detect when/if this code ever executes. Example two days ago used it to detect where the T4 beta code EEPROM write was hanging.

    As for these versions, I have never heard of them, but if it does what you want, I would try it out. Personally I would probably get one of their more expensive ones, as it gives you more speed and more sample depth. But then again my debug way is the simple easy one with my Saleae, I often set as high a rate as I can go (example with 2 channels enabled I can go 500mhz) and I sometimes setup samples to be up to 10 seconds... And then I start trace, and do what is needed to get the code to do what I am wanting to trace and then stop the capture... But that is my lazy way to do things. One can often setup to have something in the code that triggers the logic analyzer to start the capture...

    But again it depends on your needs.

  4. #4
    Senior Member PaulStoffregen's Avatar
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    I usually prefer to use my oscilloscope so I can see signal quality issues, but I do use Saleae when I need a long capture. My scope's 4M memory just isn't enough sometimes. The Saleae software also makes sweeping through a massive data set fairly easy.

    Sadly, the newer Saleae hardware (with analog channels) is very expensive. If you can find one of the older ones used, get it. Their very oldest products are also widely cloned (since they were just a Cypress FX2 chip). As with all cheap clones, you might expect quality issues or other problems, but it might be worthwhile as a stepping stone to later buying the real hardware.

    But something to keep in mind is digital-only sampling can hide signal quality problems. You also can't connect 2 resistors to a signal and see when it's "tristate" or floating. Logic analyzers are great tools when you know your signals are good, where the problem is the data itself. Issues like slow rise times and high speed effects like crosstalk between signals are usually invisible when using a logic analyzer.

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    As a beginner, my needs are a bit fuzzy but there are some use cases I can see
    - checking a clock signal I generate (is it the right frequency ? what is the duty cycle ? rise and fall time ?)
    - checking incoming digital signals from an 8 bits cpu I'm struggling with (when does this pin changes, and how over time)
    - checking how a push button bounces
    - checking what this rotary encoder produces
    and so on

    The question is, should I buy a second hand oscilloscope before a LA ? Is an oscilloscope a useful tool for the cases above ?

    Having both would be better but I've many things to buy : parts, connectors, another teensy, 2/3 breadboards, good wiring cable, some tools... and I need to make choices ;-)

    EDIT : was writing this post while Paul answered the question about oscilloscope or LA.

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    Foreword: a modern digital oscilloscope usually has basic logic analyzer functions too.

    Quote Originally Posted by Tactif CIE View Post
    - checking a clock signal I generate (is it the right frequency ? what is the duty cycle ? rise and fall time ?)
    A scope is way more appropriate for this

    - checking incoming digital signals from an 8 bits cpu I'm struggling with (when does this pin changes, and how over time)
    A logic analyzer would suffice, to a point

    - checking how a push button bounces
    Oscilloscope. Logic analyzer won't do.

    Now, a usable entry-level digital oscilloscope costs, new, about Eur 300. Lot of fun, extremely useful.

    But... an entry level logic analyzer (cheap chinese clone) costs only a few euros!
    Example (I think it's one of mine, works quite well):
    https://www.aliexpress.com/item/3296...3-8deb3c59ac4d

    Those cheap clones run with open source software (sigrok + PulseView):
    https://learn.sparkfun.com/tutorials...-pulseview/all

    It's not that I endorse purchasing cheap chinese clones, but still... I have one (two, actually, the other being a more sophisticated model) and works well.

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    Mmmm, seems that I could go the chinese clone LA route (which I can find easily on amazon) + open source software and try to buy a second hand digital oscilloscope, 40MHZ minimum in good shape (this point is obvious but as a newbie I'm unable to check if an oscilloscope is ok or not, if he can be calibrated or partially broken)

  8. #8
    Senior Member PaulStoffregen's Avatar
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    Rigol 1054Z is the cheapest "real" scope you should consider. Otherwise, hack a USB sound card for DC (costs almost nothing) and use PC scope software. Don't waste money on stuff between these. Almost all the USB scopes on the market are junk. Ancient analog scopes aren't really useful for modern microcontroller projects.

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    For what it's worth, I found my Analog Discovery 2 to be quite handy. It's an entry level scope, function generator, and a 16 channel logic analyzer. The price is alright for what you get, and the software is decent, and Linux compatible. I use the network analyzer to evaluate audio circuits quite a bit.

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    If you want to just play with a logic analyzer to see if that is what you really need all you need is a Teensy. See this thread: https://forum.pjrc.com/threads/32205...logic+analyzer. I have used it a few times and it seemed to work. Would like to eventually put it into a case etc

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    Quote Originally Posted by Tactif CIE View Post
    second hand digital oscilloscope, 40MHZ minimum in good shape
    Since "been there, done that", let me issue a word of warning: the world of digital oscilloscopes evolved at quite a speed.
    A cheap second-hand DSO from only a few years ago could potentially be far worse than an entry-level Siglent or Rigol purchased new, at not so lower a price.
    These two brands are cheap, yes, but not junk. Personally, I got a Siglent 1104 after having considered a Rigol 1054 (still very nice, at about 330 eur new).

  12. #12
    Senior Member+ Theremingenieur's Avatar
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    I'm using one of the cheapest Chinese SALEAE clones (https://www.amazon.fr/AZDelivery-Log.../dp/B01MUFRHQ2) for just 13€ (free shipping in France with Amazon prime) for 2 years now and it does its job for occasional UART, I2C, and I2S debugging very well.

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    I can confirm that. Since they are so cheap I sometimes mount them together with a small hub in the device enclosure and connect them to a few debug pins. Very convenient during development...

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    You can get those Saleae Logic clones off eBay for just a few euros/dollars. The hardware itself is basically straight clone of the older Cypress FX2LP devkit.

    I happily use one with sigrok PulseView (Download).

    It is important to realize that sigrok uses a custom open-source firmware for the FX2LP's. These devices have a minimal EEPROM, holding only the USB manufacturer:vendor identification; the firmware itself is uploaded by the "drivers" when the device is plugged in. (In sigrok case in Linux, when you select the device in PulseView; no drivers per se are installed.) Thus, the only Saleae "intellectual property" used is the hardware design of the logic analyzer -- which itself being a straightforward clone off Cypress EZ-USB FX2LP devkits and application notes, means the only way these violate Saleae rights in my opinion is mentioning them at all.

    I bought one that has no "Saleae" on it anywhere (except only in the eBay sales pitch) a few years ago for 5€ or 8€, and use it with a clear conscience in PulseView in Linux. Works well for me.
    Last edited by Nominal Animal; 06-05-2019 at 05:36 PM.

  15. #15
    Senior Member+ KurtE's Avatar
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    Note: many of these clones would actually direct their customers to use the Saleae software on their clones. Or in some cases they themselves copied down older versions of the Logic software that they would then install on their clones.

    Many of these were found and Saleae was able to get Ebay and/or Amazon or... to remove those products. Personally I consider them in the same light as those who clone things like Teensy 2 boards...

    Now if they instead point their users to open source software then great!

  16. #16
    Senior Member+ KurtE's Avatar
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    Just an FYI - Saleae does have a discount for hobby people... https://blog.saleae.com/saleae-discounts/
    Example you can get a logic 8 for: $199

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    KurtE: Definitely agreed! I have never used the Saleae code, only sigrok myself; I don't want to exploit Saleae. I even contacted the eBay seller that sold it to me, to suggest sigrok PulseView in the eBay product page instead.

    Since I happen to have a dev board and a logic analyzer clone, I took a picture of the two, so you don't need to take my word for them being basically the same:

    Larger here. The logic analyzer enclosure just snaps open/closed, there are no screws in mine.

    Both boards have the CY7C68013A microcontroller. The Atmel chips are two-wire serial EEPROMs (AT24C128 marked ATMTC169 on the dev board, AT24C02N marked ATMEL401 24C02N on the clone). The extra chip on the logic analyzer clone is an NXP LVC245 octal bus transceiver, used to buffer the logic signals. It looks like each signal has a voltage divider and a filter cap, too. My point is that considering the sigrok fw2lafw firmware works on both, the Saleae clones could be considered clones of the devkit instead, as the devices are that simple. It is the software that counts, and I definitely tell everyone I've mentioned this to use sigrok PulseView.

    Oh, and I also definitely recommend the hook-type probes with this.

    FWIW, I got an Analog Discovery 2 for 183€ via the Digilent Academic Discount and Kamami.com in Poland.

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