Electronics > Beginners

Which logic analyzer?

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Nominal Animal:
I got an Analog Discovery 2, being in a roughly similar situation. With the academic discount, I paid a total of 200€ including shipping (from Kamami).

The clincher for me was that it has two true differential input channels, max. ±25 V, at 100 Msamples/s with a 14-bit ADC. (The inputs are protected up to ±50 V.) It has an arbitrary waveform generator, 16-channel 100 Msamples/s logic analyzer, and other goodies; check the specs. The Waveforms suite has an SDK you can use to interface your own programs to the device.

I do also have a cheap Saleae clone that works really well in PulseView (part of Sigrok); Sigrok uses its own firmware for it, so there's no issue in using the cheap $7 clones with it.

tggzzz:
Things to look for in logic analysers...

Cheap logic analysers: probing and how many grounds there are? They are vital for signal integrity. Don't be fooled into thinking "I am only looking at a 10kHz clock" or "you need sampling/bandwidth of 5* the clock frequency" - even at 10kHz modern jellybean logic can have risetimes of <1ns and harmonics into the GHz region. FFI, see https://entertaininghacks.wordpress.com/2018/05/08/digital-signal-integrity-and-bandwidth-signals-risetime-is-important-period-is-irrelevant/

Triggering and filtering capabilities. There's little use in having megasamples if you can't find the ones you need! Triggering allows you to wait (hours if necessary) for the problem to manifest itself. Filtering allows you to ignore irrelevant data - most digital circuits are synchronous, so only capture the signals when the circuit will "look at" them: the clock edges.

0xdeadbeef:
For the record: you can use Zadig under Win10 to install a WinUSB driver that works with the newest version of DSView. So even the older versions of DsLogic can be used under Win10 without circumventing driver signature certification. Did this today in the company (where disabling driver certification would trigger the BitLocker password) and it worked like a charm. I couldn't tell any difference to the official driver. Bad news is that even the newest version of the SW doesn't let you change the color presets to something more eye/printer friendly.


--- Quote from: 0xdeadbeef on October 27, 2018, 10:22:45 am ---So my typical recommendation at this point would be to look out for a DSLogic Plus. Note that only the Plus version has the local RAM and only the newest HW revision has a certified driver for Win10. eBay sellers will typically try to sell the Basic version without SRAM or an older version of the Plus which doesn't have a certified Win10 driver.

--- End quote ---

rstofer:
For $150, you are in the realm of a logic analyzer of some kind.  References given above...

If you are just starting out with electronics and don't have any test equipment, the Analog Discovery 2 is the way to go.  16 digital pins with input or output and usable as a logic analyzer.  Dual channel arbitrary waveform generator, a dual power supply (current is limited, may want an external wall wart) and software to create an entire lab of instruments.  But still closer to $300 than $150.  Download and play with the free Waveforms software in Demo Mode.

Finally, the Rigol DS1054Z is less than $400 (but nowhere close to $150) and it will decode SPI, I2C and Serial on the screen.

The thing about logic analyzers is that they are just logic analyzers and almost useless for anything analog - like amplifiers or filters.  They are also questionable when timing is tight and you really do want to see that SPI CS* goes high after the last bit is shifted out.  I have a logic analyzer (https://www.sump.org/projects/analyzer/) but I use a scope much more often.

One thing to look for in a logic analyzer is external clock input (called state clock).  This is just about required to troubleshoot digital circuits with any kind of logical state and state transition.  Typically the logic will set up some next state and change to that state on the clock edge.  That's what you want to see, the current state changing to the next state.  The state value is usually a fairly wide set of digital signals.  If this doesn't seem important now, it might not be.  But it will!

tggzzz:

--- Quote from: rstofer on November 10, 2018, 01:03:53 am ---For $150, you are in the realm of a logic analyzer of some kind.  References given above...

If you are just starting out with electronics and don't have any test equipment, the Analog Discovery 2 is the way to go.  16 digital pins with input or output and usable as a logic analyzer.  Dual channel arbitrary waveform generator, a dual power supply (current is limited, may want an external wall wart) and software to create an entire lab of instruments.  But still closer to $300 than $150.  Download and play with the free Waveforms software in Demo Mode.

Finally, the Rigol DS1054Z is less than $400 (but nowhere close to $150) and it will decode SPI, I2C and Serial on the screen.

The thing about logic analyzers is that they are just logic analyzers and almost useless for anything analog - like amplifiers or filters.  They are also questionable when timing is tight and you really do want to see that SPI CS* goes high after the last bit is shifted out.  I have a logic analyzer (https://www.sump.org/projects/analyzer/) but I use a scope much more often.

One thing to look for in a logic analyzer is external clock input (called state clock).  This is just about required to troubleshoot digital circuits with any kind of logical state and state transition.  Typically the logic will set up some next state and change to that state on the clock edge.  That's what you want to see, the current state changing to the next state.  The state value is usually a fairly wide set of digital signals.  If this doesn't seem important now, it might not be.  But it will!

--- End quote ---

I agree with the above, and will note...

I am told the Rigol will only decode what is on the screen. I suspect that makes it of little use with long data comms and/or for triggering on a specific message.

Grounding is important, something that is missed in a lot of cheap amateur stuff.

For high speed signals every signal should have an associated ground, but that almost certainly isn't necessary in this use case. But good enough grounding is important to ensure the signal integrity of the voltages that the logic analyser "sees". That is especially true for any external clock signal, since if that is unreliable then all the captured data is unreliable.

I have seen some cheap LAs with an external clock but without an associated ground; I would never buy such a thing.

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