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

[UK]

Freeze! Forum police here! 

[ebastler]

I asked the admin to split of the thread, but no reply yet

Oliver, UK and eblaster !!!!
​
You took a thread from this forum that had nothing to do with your discussion and invaded it with impunity even though eblaster warned about it several times. YOUR DESIGN AND DISCUSSIONS correspond to another thread about to mimic the original POD with a faster LVDS comparator, here in this thread ANOTHER different design was being discussed, simpler, limited but cheaper in which your ideas and designs DO NOT apply. On top of that, you introduces a lot of confusion in this thread and it is no longer even easy to follow the versions when you filled the last three pages with vanilla connector arguments.

PLEASE, next time respect the other threads that have nothing to do with what you are like to discuss!

Next time you might want to ask ChatGPT to word your message. It tends to get the tone about right.

Yes, this discussion of a "proper", comparator-based logic probe has become bigger than Oliver originally expected. So what do you propose we do about it? Users cannot move parts of a thread to a new one; Oliver asked the moderators but they did not get around to it, or did not consider it worthwhile. So what?

As threads on this forum go, I think the past pages have been one of the more productive examples. Something actually gets developed, in a joint effort, with feedback on improvement ideas. Much better than the haggling we get in some other threads. And yes, the connector discussion is highly relevant in this context. Guess what? Using a standard ribbon cable with 50 conductors to the probe sucks.

If you are interested in the cheap solution, since all you want to probe is 5V and 3.3V logic: Buy a complete LA probe on ebay for $75 including cheap grabbers; problem solved.

[Tarloth]

eblaster and UK, You can discuss all you want about the solution you are thinking and off course about the connector variants, but in the appropriate thread, a new one or the original one, not this, and the same eblaster warned about this is not the appropriate thread several times but continues writing in the wrong thread.

In this thread, having daughter boards was not even being discussed, just a simple, inexpensive and direct signal adapter between the grabbers and the oscilloscope. Many of us don't need more than that and we are interested in maintaining the original thread with the ideas from the original thread straightforward.

By the way, I have tons of original pods from HP signal analyzers with higher quality grabbers than cheap one in ebay, and even than the original from Rigol. You can say that flat cables suck but it turns out that they have been used for years by the big brands. Agilent for example still uses flat ribbon in pod's of almost 4GSa/s. It's ok if you don't like them, but for some of us, who think perhaps in more pragmatic (conservative? budget?) terms they seem sufficient for an oscilloscope under $1000 (or 10K by the way). Because of that in this thread the board keep simple.

On the other hand, I don't have to buy a $75 LA because I didn't agree with your point of view! With the same argument I would tell you to go and buy the original Rigol! It's great to discuss alternatives to commercial products, I just ask that they be done in the appropriate threads for each initiative.

The only thing I'm asking you is to respect the threads, and continues arguing in the appropriate one when you originated the discussion. This thread also has a very productive discussion, similar to the one originally proposed by Sr Gandalf but from an even simpler approach.

[Mechatrommer]

as long as discussion circling around somewhat evolution or improvement to the probe, i'm fine... btw, is there any clear diagram rev eng people made about what every single pin does on the MSO5000's 2x25 2.54mm pitch LA connection? (i guess should be the same/compatible with DHO900) all i've seen so far are finished diy probe product... what if i want to make my own LA probe? if there is diagram, i dont have to redo rev eng...

[ebastler]

btw, is there any clear diagram rev eng people made about what every single pin does on the MSO5000's 2x25 2.54mm pitch LA connection? (i guess should be the same/compatible with DHO900)

See below, for example. And yes, it's the exact same pinout on the MSO5000 and DHO900. (The DS1000Z plus has a slightly different connector. Same signals, but more GND pins and hence 68 pins in total, I believe.)

https://www.eevblog.com/forum/testgear/rpl1116-active-logic-probe-pod-for-1000z-series-teardown/msg2419002/#msg2419002

EDIT: If you want to design your own probe, don't talk about it here or Tarloth will get mad at you... 

[Tarloth]

EDIT: If you want to design your own probe, don't talk about it here or Tarloth will get mad at you... 

eblaster, you are really behaving in a way that is not only dishonest but also quite unfair.

I am NOT saying that discuss about make a version of LA is wrong, I affirm that it's quite positive, I ask only that it be done in the corresponding thread:

* Original thread https://www.eevblog.com/forum/testgear/rpl1116-active-logic-probe-pod-for-1000z-series-teardown/ (which is where someone started arguing about the USB-C vs mini connector HDMI) attempts to replicate the original Rigol board using high-speed comparators and can adapt to different logic levels. It is the most complete and expensive, and includes several improvements to the original Rigol adapter.

* This other thread https://www.eevblog.com/forum/testgear/ms05000-budget-logic-analyzer-probe-set-design/ started by Gandalf_Sr, it's based on adapting only logic signals (3.3 volt and 5.5 perhaps some other in positive low voltage) but using one board on the oscilloscope side to tidy channels and two independent pods (connected via a flat ribbon cable) with 8 channels. Each board include logic to LVDS converter and a level converter that can even use the voltage present on the analyzed board for flexibility. This design ignores the signals from the oscilloscopes that configure the logic level. Only one logic level for each daughter board,

* This thread, started by S. Pethrukin, is for those who are discussing a signal adapter PCB for 3.3/5 volt logic only, using a 5 volt tolerant digital-LVDS converter. It is a single board budget project, the grabbers go directly to the PCB that adapts the signals between they and the oscilloscope. No differential cables between boards, perhaps a flat ribbon cable from old SCSI drives to connect the board to oscilloscope for more freedom. It is the cheapest of the three threads.

Each thread has a obvious target and budget. Three different ideas with the same objective, BRAVO! But each one has its problems and targets so it is more neat to keep them organized and tidy, but that's why the threads exist in forum.

By the way, YOU notice that this is not the thread to discuss about the diferential connectors between boards in those post

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?

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/.

The present thread is the "low cost probe" one, which originally focused on the cheaper CMOS/TTL-level pods only. As mentioned a few posts above, I have found the other relevant thread in the meantime. It looks into using the original LMH732x comparators, and has a few schematics and layout suggestions for those: https://www.eevblog.com/forum/testgear/rpl1116-active-logic-probe-pod-for-1000z-series-teardown/.

[Simon]

If you can find me a thread  that 10 pages in has stuck band on topic I will devise a medal for you!

[ebastler]

@Tarloth -- you come into this thread complaining and shouting at us, then you follow up with two dissertations. You still have not answered my question in response to your initial complaint: What do you expect Oliver, UK or me to do with this thread now? Delete all our posts?

[Tarloth]

If you can find me a thread  that 10 pages in has stuck band on topic I will devise a medal for you!

Yes, the second link https://www.eevblog.com/forum/testgear/ms05000-budget-logic-analyzer-probe-set-design/

[Tarloth]

@Tarloth -- you come into this thread complaining and shouting at us, then you follow up with two dissertations. You still have not answered my question in response to your initial complaint: What do you expect Oliver, UK or me to do with this thread now? Delete all our posts?

First of all, english it's not my first language (I assume it's not yours either) and sorry if you fell agreded but I ask you for not invaded unrelated thread next time. As answer to my post accuse me of Police (I ask for rule's compliance) and you tell another user that I am against the discussion of new ideas, which is not true, I just asked you for little order and not to continue writing in this thread or in the future not to invade threads not related to their discussion . An user that are interested in the original post need's to navigate several pages unrelated to the topic and perhaps lost information that it's relevant to this low cost solution.

To put in black and white, I intend that if on October 26 you had already detected that this was not the thread to discuss this topic, at least maintain some order and go to discuss in the thread that you yourself said should be used. And if the moderators don't move the posts, at least  don't continue generating discussion pages here that belong to another thread and continue where your topic belongs. It wouldn't be relevant if with the first post hadn't realized that was the wrong thread, but you in particular detected it and reported it at least 3 times and didn't care. That's annoying.

When you just discovered that were on the wrong thread, you could have copied posts to the other thread and deleted these and everything was in order. Now that it's impossible, only if a moderator do that.

Please, respect the topic of a thread, It is a way to respect the discussions of other people and keep the forum organized. It is simply respect for the other people who are discussing other things unrelated to your discussion, that is very interesting and important, but in their corresponding place.

Have you a nice day

[Mechatrommer]

can someone re-explain how 49.9ohm and 220ohm resistors form 1/10X attenuation? i read the original rigol la probe limit is 40V, 1k ohm input impedance? this is mind boggling.
i'm referring to this post: https://www.eevblog.com/forum/testgear/rpl1116-active-logic-probe-pod-for-1000z-series-teardown/msg2088667/#msg2088667

[ebastler]

can someone re-explain how 49.9ohm and 220ohm resistors form 1/10X attenuation? i read the original rigol la probe limit is 40V, 1k ohm input impedance? this is mind boggling.
i'm referring to this post: https://www.eevblog.com/forum/testgear/rpl1116-active-logic-probe-pod-for-1000z-series-teardown/msg2088667/#msg2088667

You need to look at the input side of the comparator, with a 10k/(90.8k+10k) divider. You were looking at the termination resistors for the differential output.

[Mechatrommer]

can someone re-explain how 49.9ohm and 220ohm resistors form 1/10X attenuation? i read the original rigol la probe limit is 40V, 1k ohm input impedance? this is mind boggling.
i'm referring to this post: https://www.eevblog.com/forum/testgear/rpl1116-active-logic-probe-pod-for-1000z-series-teardown/msg2088667/#msg2088667

You need to look at the input side of the comparator, with a 10k/(90.8k+10k) divider. You were looking at the termination resistors for the differential output.

i thought the bottom side is the input, no? so that means, top side is the input?

[ebastler]

i thought the bottom side is the input, no? so that means, top side is the input?

In the schematic in the post you linked to, the inputs are on the left side of the comparator: The probed signal on IN+, the reference level (threshold) on IN-. The relevant voltage divider is on the IN+ signal.

The resistors you talked about (49 Ohm and 220 Ohm) are shown on the right side of the comparator. That's where the two differential output lines are. The resistors do not form a voltage divider; these are termination resistors.

Are you sure you should be considering your own probe design? 

EDIT: Ah, you were now talking about the photo? Better use the schematic if you want to study the circuit design... But yes, on the photo the differential outputs are on the bottom -- which is why there are twice as many connections.

[Mechatrommer]

Are you sure you should be considering your own probe design? 

i'm currently trying to understand this thing inside out while i have time and interest. including evaluating pre-existing diy and original design how and why they do it.. just now trying to find comparator replacement to unobtanium LMH7322 (LMH7324 also not available from the sources i usually buy things from), not an easy task.. currently listing as possible/cheaper replacement ACDMP 607/562/564/567 but they are equally hard to find or expensive. LT1715 is cheaper, but probably crippled and 4ns prog delay may put some people off. what i dislike about pre existing is their form factor, large IDE connectors here and there and right angle connection, i prefer if possible much compact version with nice 3d printed casing... so i'm still evaluating, no conclusion yet, just learning.

In the schematic in the post you linked to, the inputs are on the left side of the comparator: The probed signal on IN+, the reference level (threshold) on IN-. The relevant voltage divider is on the IN+ signal.

ah sorry i didnt notice there is diagram attached below that post. thanks.

[ebastler]

just now trying to find comparator replacement to unobtanium LMH7322 (LMH7324 also not available from the sources i usually buy things from), not an easy task..

I doubt you will find anything compatible and cheaper. They are available from e.g. Mouser and Digikey, aren't they?

Make sure to look not only at the input specs (levels & speed), but also at the differential outputs. You need RSPECL (Reduced Swing Positive Emitter Coupled Logic) outputs to make your scope happy.

[Mechatrommer]

just now trying to find comparator replacement to unobtanium LMH7322 (LMH7324 also not available from the sources i usually buy things from), not an easy task..

I doubt you will find anything compatible and cheaper. They are available from e.g. Mouser and Digikey, aren't they?

i'll try to find cheapest source i can get first, even from aliexpress 8pcs ADCMP576 alone will cost me $69, mouser and digikey will cost much more damage to my place guaranteed. 10pcs LT1715 is $37 though, but not look deeper on suitability. if no cheaper option, or if its not worth the effort to redesign, then i might just get the $75 probe from ebay, but then not sure what ic it is using. no prog delay spec no BW no nothing, so its shady.

Make sure to look not only at the input specs (levels & speed), but also at the differential outputs. You need RSPECL (Reduced Swing Positive Emitter Coupled Logic) outputs to make your scope happy.

not sure about this yet, limited reading resources. but isnt LA input (comparator output) directly connected to DHO FPGA? ie just logic input 0 and 1? as long as within voltage limit range it should be ok, no?

[ebastler]

if no cheaper option, or if its not worth the effort to redesign, then i might just get the $75 probe from ebay, but then not sure what ic it is using. no prog delay spec no BW no nothing, so its shady.

The low-cost probes do not use comparators with an adjustable threshold, but simpler LVDS drivers -- SN65LVDS1DBVR or similar multi-gate parts. You might be able to spot on the ebay photos what has actually been populated.

not sure about this yet, limited reading resources. isnt LA input (comparator output) directly connected to DHO FPGA? ie just logic input 0 and 1? as long as within voltage limit range it should be ok, no?

The FPGA inputs are configured for LVDS (low-voltage differential signaling), and the comparator voltages are chosen such that the RSPECL outputs are compatible with that. You will need differential outputs on the comparator; they could be LVDS instead of RSPECL, I guess.

The LT1715 you mentioned does not have differential outputs, and its output voltage might damage the FPGA's LVDS inputs? LVDS logic levels are only 1.0V and 1.4V; not sure what the FPGA can tolerate as absolute maximum ratings.

[Mechatrommer]

The LT1715 you mentioned does not have differential outputs, and its output voltage might damage the FPGA's LVDS inputs? LVDS logic levels are only 1.0V and 1.4V; not sure what the FPGA can tolerate as absolute maximum ratings.

yes noted with concern, thanks for the info... while working on another section of dho, i got stucked since some parts havent arrived yet so i start doing reading on LA section, and i managed to pop something out of my fw hacked dho804 with help from diagram you provided earlier, without needing to flow solder the 2x DDR3L RAM in, so there's interesting hope. interestingly, sampling rate and memory depth not reduced so bad when this got activated as somebody else reported/portrayed much earlier. only halved and thats not too bad, its normal imho. 625MSps still can debug 300MHz 16ch logic, yes? 

ps: i guess low cost probe for DHO800/900 and discussions should not be posted here right? otherwise police will tantrum? i prefer to call "advisor" because advisor we can ignore, police if we ignore, we will go to jail, or got banned and cannot post in forum anymore. i sometime will become nonsense advisor myself

[ebastler]

while working on another section of dho, i got stucked since some parts havent arrived yet so i start doing reading on LA section, and i managed to pop something out of my fw hacked dho804 with help from diagram you provided earlier, without needing to flow solder the 2x DDR3L RAM in, so there's interesting hope. interestingly, sampling rate and memory depth not reduced so bad when this got activated as somebody else reported/portrayed much earlier. only halved and thats not too bad, its normal imho. 625MSps still can debug 300MHz 16ch logic, yes? 

Be careful when probing around and making connections across the 50-pin connector! There are definitely voltages there which the LVDS inputs won't like, including negative voltages.

The 625 MHz sampling rate for the LA is as expected, and I agree that it is adequate. A bit inconvenient maybe that it's such an odd number. The remaining 625 MHz for a single analog channel, or only 156 MHz when using 3 or 4 analog channels, are the disappointing part. (And the part which is not "normal" -- the analog sampling rate in MSOs is typically limited by the ADC, and does not get reduced when digital channels are activated.)

That AWG board looks promising!   But yes, let's be good boys and move this scope-specific discussion to the DHO800 hacking thread.

[UK]

i guess low cost probe for DHO800/900 and discussions should not be posted here right?

A new thread will be better since many new users come here for the DHO800/900 series. They won’t think to look for information in the MSO5000 threads and may easily miss it.

[Mechatrommer]

Be careful when probing around and making connections across the 50-pin connector! There are definitely voltages there which the LVDS inputs won't like, including negative voltages.

thanks to the diagram you provided. made some probing earlier, i believe whats missing is 4V rail. but i got MPM3630 already in case i need it.

i guess low cost probe for DHO800/900 and discussions should not be posted here right?

A new thread will be better since many new users come here for the DHO800/900 series. They won’t think to look for information in the MSO5000 threads and may easily miss it.

agreed. i'll make another new sub thread when something practical achieved.

[Tarloth]

ps: i guess low cost probe for DHO800/900 and discussions should not be posted here right?

NO, THIS IS THE thread OF THE LOW COST PROBE, your posts are in the wrong place, but some people not understand 

[Mechatrommer]

ps: i guess low cost probe for DHO800/900 and discussions should not be posted here right?

NO, THIS IS THE thread OF THE LOW COST PROBE, your posts are in the wrong place, but some people not understand 

which one of my post is not about low cost probe?

[UK]

I assume he just saw a 'DHO800/900' model name in the thread of the MSO5000 probe.
Hope this dude never gets any sort of gun or police badge in real life. 

I'm a bit nervous when he starts writing in all caps.