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LaPOD: Low cost Logic Analyzer probe for MSO5k, DHO900 and more!

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ebastler:
Congratulations on solving that puzzle -- nice job!

EDIT: Looking again at the layout, I think there is a bit more puzzling to be done. The orange traces in general don't look length-matched to me; the traces for IN9 in particular are much shorter than any of the other pairs?

On the silkscreen, and also when you create a new thread about this, I would not call it an "MSO5000" LA board. The new DHO900 series (low-cost 12 bit scopes) uses the exact same pinout for the LA probes, and will certainy get a lot of attention. So be sure to let those users know about your probe too!  ;)

If you could take a moment to address my earlier question? Thanks!


--- Quote from: ebastler on October 26, 2023, 12:38:56 pm ---Could you point to those designs you used as a starting point? I had come across a thread once which aimed to do a full-spec replica of the Rigol probe, but it is not this thread here, right?

Also, could you restate the comparator part numbers please? Are they LMH732x?

--- End quote ---

tooki:

--- Quote from: UK on October 07, 2023, 11:34:09 pm ---Okay, now it makes sense. But why not a Mini DisplayPort, it's smaller but has all the same.
Or even a full-size DisplayPort, since it has a fixing feature.

--- End quote ---
The full-size DisplayPort is possibly the least-reliable connector I have ever encountered. Because of how the plugs are implemented (a PCB with the contacts soldered to each side, and the wires from the cable to that PCB, but not overmolded because of the latching release button), they are extremely susceptible to damage from bending. Literally every DP cable I’ve encountered in the wild has had to be replaced at least once. Mini-DP is a far more robust connector.


--- Quote from: oliv3r on October 15, 2023, 09:02:03 pm ---Those thoughts crossed my mind too, but mini-hdmi connectors are much harder to source; but what's worse, mini-hdmi cables are much harder to source :)

also, as you can see, from a size point of view, it doesn't matter much.

same goes for displayport. HDMI you can get for a couple of € from action or poundshop or what not. They are 'ubiquitous'. Even when the HDMI consortium is evil ;)

--- End quote ---
They didn’t say mini-HDMI, they said mini-DisplayPort. They are available.

The biggest risk with using popular connectors like HDMI for some other signal is what happens if someone connects a cable with an actual HDMI signal to it. (Not entirely crazy, given how modern scopes have HDMI outputs.) Will it damage your device? Will it damage the HDMI device?

In this regard, a more obscure connector — or one which was not designed specifically for a common consumer use — is a better choice.

ebastler:

--- Quote from: tooki on October 28, 2023, 01:45:45 pm ---The biggest risk with using popular connectors like HDMI for some other signal is what happens if someone connects a cable with an actual HDMI signal to it. (Not entirely crazy, given how modern scopes have HDMI outputs.) Will it damage your device? Will it damage the HDMI device?

--- End quote ---

At least oliv3r is in good company there: Siglent use an "HDMI" connector for their proprietary S-BUS interface to an external logic analyzer module. It's right on the front panel of various entry-level scopes.  ::)

Looking at the renderings above again, I have a different concern about the full-size HDMI connectors though: @oliv3r, is there enough room for the HDMI plugs' plastic bodies? Looks like the jacks are spaced very closely together.

UK:
And I think so too, there isn't enough space between the ports... especially for standard cheap cables.

As a possible option to solve the problem with the PCB dimensions is to swap the current HDMI sockets to the upright/vertical version.



ebastler:

--- Quote from: ebastler on October 26, 2023, 12:38:56 pm ---Could you point to those designs you used as a starting point? I had come across a thread once which aimed to do a full-spec replica of the Rigol probe, but it is not this thread here, right?

Also, could you restate the comparator part numbers please? Are they LMH732x?

--- End quote ---

Answering my own question, since oliv3r seems to drop in only sporadically:

The thread on analyzing and replicating the original MSO5000 logic probe (PLA2216) is here: https://www.eevblog.com/forum/testgear/rpl1116-active-logic-probe-pod-for-1000z-series-teardown/. And the comparators are indeed the LMH7322 (dual comparator) and LMH7324 (quad). Both are available from Mouser etc., and both are on the expensive side.

Regarding the form factor of a logic probe, I am not sure whether I prefer Rigol's approach (all 16 channels routed to a large external pod) or oliv3r's (4 pods with 4 channels each). Rigol's design clearly limits flexibility, requiring all 16 probed channels to be relatively close to each other on the PCB under test; and it has the bulky, broad flat cable connection. But four HDMI cables can get a bit messy too...

And it's worth mentioning that Rigol tells you not to hot-plug the logic probe connector! Having those individual HDMI-style jacks on the front may just be too tempting?

The other thread has one version with 4x4 channels, but using USB-C connectors -- debatable, since inserting the plugs the wrong way round will swap the channels, it seems.  It also includes a design for 2 pods with 8 channels each, connected via narrower flat cables. That one might actually hit the sweet spot for me -- but I am not sure whether it was fully polished and tested.

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