[sdiy] Logic Analyzers

Michael Zacherl sdiy-mz01 at blauwurf.info
Thu Dec 28 16:29:57 CET 2017

Gentlemen, many thanks a lot for your replies, quite something I’ve to look through!

> On 28 Dec 2017, at 12:37, ASSI <Stromeko at nexgo.de> wrote:
> Am 28.12.2017 um 03:22 schrieb Michael Zacherl:
>> In the not so distant future I’ll be probably in the market for a not too expensive logic analyser.
>> Just browsed the Saleae site, looks good at the first glance.
>> What’s to have? What’s to avoid, feature-wise?
> You really need to define your objectives in more detail, make a list of "musts", "nice-to-haves" and "don't cares" and just fill that out for each of the options you come across.  

Achim, you’re right, you got me here.
I got the idea to consider getting an analyser quite a while ago and my hasty question was triggered by Jay’s response in the former thread.
And I realise, my questions are way too vague and, in fact, too early to ask.
Also I have to refresh my memory since I didn’t use a logic analyser for decades. Last time that was some very decent HP box, money-wise way above any budget I ever had. I remember trouble shooting an S-100 bus system back then.

> What's "not too expensive" for you?  

The first product I looked up yesterday was the aforementioned Saleae and the $1k of the Logic Pro 16 didn’t shock me.
So - _if_ I went for an analyser €1-2k would be feasible, I think. 
Of course I looked up a Tektronix MSO58, Jay dreams about. Well that's like 20 times+ the money I mentioned above. ;)
But I certainly think that neither the requirements nor my skills would justify acquiring such a device, even if I could afford it!

> How many channels do you want, do you need hardware buffering or hardware triggering, target synchronous sampling.  Is protocol analysis in the viewer software enough or do you need to trigger on protocol events?  What protocols do you need to analyze, do you also need to be able to inject protocol events?  How about the higher levels of the protocol stack?  Is Windows only OK or do you want Linux software also? Etc. pp.

ATM I don’t think I’d need anything protocol related - for the time being. But you know, never say never.
So maybe an upgrade option could be one criterion for the buying decision. 
Reading bus signals (I don’t think >50MHz) would be one of the, maybe _the_ target/s, so many channels would be an issue. 

> At home I have an original Saleae Logic/8, an Intronix LogicPort and a PropScope.

Apparently PropScope is going EOL … final sale for $100: https://www.parallax.com/product/32220

>  All three would somehow fit your description, but of course they are very different things even though there is overlapping functionality.  

One thing I had to realise is I’d rather often would need a Windows computer to run a particular product, which I don’t have.
So I’d depend on macos or Linux support. One thing I almost overlooked when browsing the Net for options.
So maybe looking at this sigrok software, Steve mentioned,  would be an idea.

> The LogicPort software fortunately works with Win98SE and doesn't really need much in the way of USB and CPU performance, so I use it with an old 10" laptop that already had a touchscreen at the time.  That combination is a lot more usable than some hardware LA out there and I've used a few.

> For all software based instruments you also need to consider how the necessary PC or laptop fits into your work area.  I recommend to use a dedicated box so that you can freeze the software stack in a known working state if you need to.  Keep in mind that those analyzers having no hardware buffers (like the Saleae Logic) need pretty much all the USB performance they can get if you use them at speed and won't work nicely through most USB hubs (either due to bugs in the hub or the additional latency).  

which of course would be an issue when reading many channels (busses) at higher speeds.
and yes, USB hubs are a pain … always had troubles in much simpler applications.

> Unfortunately that description includes many laptop USB ports these days, so unless you buy that laptop specifically with those requirements in mind you may end up with the only port working well in an entirely inconvenient location for instance.

I got some old hardware around - so reviving that with, say, Linux could be an option.
But then, I sense, hardware buffering/triggering would be a necessary feature.

Also, and that gets me back to the “_if_ I went for an analyser” statement, maybe I should put the money into a decent DSO to complement my old 100MHz analogue scope, which I love!

And I realise, I’ve to do quite some homework before asking further questions.
Tektronix and others have some good primers on their product ranges - that should update me accordingly.
Thanks a lot - m.

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