DIY Logic Analyzer Probe and Pods for Siglent (and LeCroy) scopes

[AVGresponding]

Calling something "compatible" implies a matching of capabilities.

When one finds oneself at the bottom of a deep hole, it is usually advisable to cease digging.

[tautech]

@Johnny B Good

I was pondering this for a bit and decided to take a look at the original files. I think I know where the confusion came from.

In his (oz2cpu's) original design there was no ground fill on the top and bottom. If this had been made by simply omitting the inner layer gerber files then it would have not worked. When I edited the files I added a ground pour to the top and bottom to add a continuous ground throughout. If this was a microwave circuit then it would have not been appropriate to do so without net via shielding and recalculating the width of the traces. But for the frequencies involved I feel like it was appropriate and the coupling between the sides is insignificant compared to the input impedance. The only concern you should have is about the ribbon cable. But I do mention in the listing that it was designed for 120 ohm cable and that I did not include it, so I feel like I was being fair by mentioning that.

I don't want to get into an argument about international law here. Suffice it to say, I am well within my rights to reproduce a non-patented hardware design or take inspiration from one. Your concern should only be if I am attempting to defraud you, which I'm not. I have tested this and it works. That's all I can say to convince you. Really, all you had to do was test it and talk to me. I have had to work with people who have burned PCBs with a torch and want a refund. If you buy it and it doesn't work then deal with me that way. Starting with accusations is not productive between a buyer and a seller.

You're advertising: Siglent SPL2016 Compatible DIY Logic Probe
That it certainly isn't ! ! !

While it may fit a SDS2000X+ DSO and behave similar to SPL2016 it can in no way challenge the original performance.
Best you have a squiz at the specs here:
https://siglentna.com/wp-content/uploads/2021/05/Digital-Probe-Datasheet-V20E201912.pdf

FYI, original SPL2016 are supplied with 20 quality grabbers and not some POS grabber that falls of if you sneeze on it.
Offering a cheap low level substitute DIY MSO probe that fits a SDS2000X Plus would be well advised rather than mention of SPL2016.

Siglent SPL2016 Compatible DIY Logic Probe

Think please.

I think NOT !

This same PCI-e design is used by Tek, LeCroy, Rigol and probably others too, all with specs that your DIY version cannot duplicate.
Yes, it's a DIY MSO probe that fits SDS2000X+ models for the purpose of this thread but SPL2016 is in a totally different class.

[rogersstuart]

@Johnny B Good

I was pondering this for a bit and decided to take a look at the original files. I think I know where the confusion came from.

In his (oz2cpu's) original design there was no ground fill on the top and bottom. If this had been made by simply omitting the inner layer gerber files then it would have not worked. When I edited the files I added a ground pour to the top and bottom to add a continuous ground throughout. If this was a microwave circuit then it would have not been appropriate to do so without net via shielding and recalculating the width of the traces. But for the frequencies involved I feel like it was appropriate and the coupling between the sides is insignificant compared to the input impedance. The only concern you should have is about the ribbon cable. But I do mention in the listing that it was designed for 120 ohm cable and that I did not include it, so I feel like I was being fair by mentioning that.

I don't want to get into an argument about international law here. Suffice it to say, I am well within my rights to reproduce a non-patented hardware design or take inspiration from one. Your concern should only be if I am attempting to defraud you, which I'm not. I have tested this and it works. That's all I can say to convince you. Really, all you had to do was test it and talk to me. I have had to work with people who have burned PCBs with a torch and want a refund. If you buy it and it doesn't work then deal with me that way. Starting with accusations is not productive between a buyer and a seller.

There is no confusion. You took well made board and fiddled with it making it worse. Designer is an engineer and several others made the copy and verified design. It is good. Proven.

Removing inside ground planes completely destroyed AC return paths underneath the signals. Pouring ground on top did nothing except added DC return path. Sampling frequency and repetition frequency of signals on DUT doesn't matter. Only rise/fall times matter and even with Arduino pins you can get frequency spectra up to 1 GHz, believe it or not.. Raspberry PI has sub nanosecond edged on it's pins, it's even faster. This induces ground bounce, crosstalk and ringing. Thomas spent time designing this with good signal integrity, and did a decent job of it.  There were some other attempts and they could see spurious pulses and noise that is not there. Not with oz2cpu though. It works well.

Designer doesn't mind you making boards and selling them for those who cannot be bothered to order them by themselves. All you needed to do was make them EXACTLY how they were designed, and somewhere in text give design credits to him... And they would work really well.. And I bet you that someone would mention it here as an good purchase option and you would get additional sales..

I understand the harmonics of a square wave. I think 1 GHz is a bit far out and this isn't a narrow bandpass filter or anything where a high degree of accuracy is needed. If you read the listing I mention that the original design was for 120 ohm cable and that I have included an alternative ribbon cable that worked for me. The component values are as the designer specified.

No one is reading and interpreting. There is just an onslaught of people making assumptions and not testing the reduced cost design. It was too expensive for my tastes to include the inner layers on that tiny board. I don't mention that the extra copper is or isn't included, say where I got it, or provide any implied warranty. Furthermore, I'm not advertising. Don't buy it. It takes up my time. I just like selling things on eBay. It gives me something to do sometimes.

With all that being said, I'm not the kind of guy who won't listen. If you buy one and see that it doesn't suit your needs then just say so. And that's it. It won't damage your scope. If you feel like the signal integrity is bad then what option do I have other than offer you a refund and investigate your claims?

[rogersstuart]

Calling something "compatible" implies a matching of capabilities.

When one finds oneself at the bottom of a deep hole, it is usually advisable to cease digging.

Compatible means that you can plug either into your scope and it will function. I think it's unreasonable to expect identical performance for $20 but if you do, well there are more than 7 billion people out there and everyone is free to have their own opinion.

[Johnny B Good]

@rogersstuart

 I was prompted by oz2cpu's sneaking suspicion that the main PCB may not have been an exact replica of his original 4 layer board and the great importance he places on it meeting this requirement, to verify whether it was a 4 layer board or not. You answered the question honestly and I thank for clarifying that point.

 I sought further advice from oz2cpu before making any decision to cancel the order since your stated eBay policy is "no returns", denying me the opportunity to 'buy and try' as you've just suggested. Cancelling the purchase whilst this was still possible seemed the best option all round and I thank you for deferring to my cancellation request and the speedy refund.

 Since the Belden ribbon cable undoubtedly accounts for most of the high levels of crosstalk shown by the graph you took the trouble to publish, it's impossible to say how much of a problem the lack of the inner groundplane shielding layers would be in this case.

 Since oz2cpu had stressed the importance of a 4 layer PCB, I deferred to his judgement over your claim that this wasn't really that important after all. You may be right but there is no way to prove this, short of actually testing using twisted pair or coaxial cabling between the main PCB and the pods.

 One way around this issue with your version of the main PCB, would be to wire up a pod using twisted pairs or coaxial cables and generate a new crosstalk graph for comparison against the Belden cable you're supplying as a courtesy to those with a more modest initial performance requirement.

 Provided you've made it clear up front that the main PCB is only a two layer version of the original design and spell out your reasons for this cost cutting choice, backed up by the new graphical evidence obtained using twisted pair or coaxial cables, I should think you wouldn't have any further problems in this regard.

 Supplying only a single 'starter pack' of test clip leads isn't such a bad idea since the quality and price of these test clips can vary considerably and it's best to economise here and allow the end user to make their own choice in the price/quality equation.

[rogersstuart]

@rogersstuart

 I was prompted by oz2cpu's sneaking suspicion that the main PCB may not have been an exact replica of his original 4 layer board and the great importance he places on it meeting this requirement, to verify whether it was a 4 layer board or not. You answered the question honestly and I thank for clarifying that point.

 I sought further advice from oz2cpu before making any decision to cancel the order since your stated eBay policy is "no returns", denying me the opportunity to 'buy and try' as you've just suggested. Cancelling the purchase whilst this was still possible seemed the best option all round and I thank you for deferring to my cancellation request and the speedy refund.

 Since the Belden ribbon cable undoubtedly accounts for most of the high levels of crosstalk shown by the graph you took the trouble to publish, it's impossible to say how much of a problem the lack of the inner groundplane shielding layers would be in this case.

 Since oz2cpu had stressed the importance of a 4 layer PCB, I deferred to his judgement over your claim that this wasn't really that important after all. You may be right but there is no way to prove this, short of actually testing using twisted pair or coaxial cabling between the main PCB and the pods.

 One way around this issue with your version of the main PCB, would be to wire up a pod using twisted pairs or coaxial cables and generate a new crosstalk graph for comparison against the Belden cable you're supplying as a courtesy to those with a more modest initial performance requirement.

 Provided you've made it clear up front that the main PCB is only a two layer version of the original design and spell out your reasons for this cost cutting choice, backed up by the new graphical evidence obtained using twisted pair or coaxial cables, I should think you wouldn't have any further problems in this regard.

 Supplying only a single 'starter pack' of test clip leads isn't such a bad idea since the quality and price of these test clips can vary considerably and it's best to economise here and allow the end user to make their own choice in the price/quality equation.

No returns is just a psychological thing and part of doing business on eBay. I do not want to pay for shipping to Europe. There is no such thing as no returns on eBay once someone opens a dispute. I would prefer to leave people feeling satisfied even if that means a loss here or there.

I feel like I should not have responded because the thread has been derailed now. I saw mention of opening a dispute and you sounded upset, so I said something. I was worried that someone might act maliciously assuming that I'm a bad actor out to scam people.

I agree with you about the high level of crosstalk. I'm not sure what it should be. At best it is -15 dBm below 100 MHz, at worst it is -8-7 dBm. Though, I have to admit that I'm not sure if I measured it correctly. I soldered female DuPont connector pins to SMA connectors and measured S21 using my 75 OHM VNA that was calibrated with 50 OHM Rosenberger "standards" in a 50 OHM system impedance to the end of the cable. I had to bend the pins a little and jam them in there. It was pretty sketchy. I have been told by the designer of the 8753E that it is acceptable to mix impedances like this. Recently I have found that adding pads can clean up a trace and improve accuracy. I would measure it that way now and might see a slight improvement.

I also normalized the data from 50 ohms to 120 ohms based on the 120 ohm cabling that is specified. I'm not sure if it was correct to do so.

As someone had mentioned, the clips that I include are the cheap kind. You know, I wish I could provide good ones but I couldn't find a supplier for them at a low enough price. I say that you get 8 but you would actually receive 10 in case 2 are bad. I count out 10 for each bag and inspect them all. It's really just tacked on so someone can immediately test their build. It's just as cheap for you to buy more on Aliexpress as it is for me to. I don't have a specific markup for this product. All I can say is that I'm selling it for at least half of my calculated price so I'm trying not to add extra things or make it more complicated.

[natman69]

I am interested in building the logic probe for Siglent SDS oscilloscope based on this thread project (many thanks to oz2cpu and other forum members for their amazing work  ).
So if someone it is also interested, I suggest to group buy PCB assembled with SMD passive components from JLCPCB or other suppliers.  Maybe also 3D printed enclosures and cables.

[rogersstuart]

I kept thinking about this so I decided to go back and see if I can find better answers. It appears that oz2cpu's design (and the HP design his was inspired by) are meant to form a voltage divider. I used a VNA to generate a model of the digital input to use as termination. I would have preferred to know exactly what components are used internally but I couldn't find a picture of both sides of the scope PCB. It's 10k DC which leads me to believe there's more to it than TVS diodes and the comparators.  I also used measurements of 24" of the ribbon cable I have on hand in a GSG order. All connected by co-simulations of the PCB layouts. I was able to select a reasonable set of values to get a 1/10 voltage divider action and the waveform looked okay. Since this was based on my own measurements and I only have so much confidence in my setup and skills, I admit that there is probably some error. The values provided by oz2cpu produce a squarish waveform in the simulator with a close to 1/6 voltage division which is (for me) good enough to back my assertion that this is meant to be a voltage divider.

As expected, there was some coupling between the top and bottom traces. I isolated a segment from where the 120 ohm resistor is to the card edge. At worst you can expect 6.2% voltage coupling (700 MHz) with a 10k load and near 1.3% at 1 MHz. The amount of signal that makes it through decreases with increasing frequency which affects that number (increase).

I tested swapping the 8.2p capacitor for a 20p capacitor and swapping the 120 Ohm resistors for 100 Ohm resistors. With my function generator referenced to a 10 MHz square wave being generated by my scope I saw little to no difference between the original or either modified component selections. With the 20p capacitor maybe there was a moment of jittering while handling the probe. Of course, this was best case since the sampling should have been fully synchronized with the waveform generator. All this tells us is that the waveform was not distorted enough to be unusable. I did not try swapping the 86.6k resistor. My simulations indicated that a wide range of values (as low as 20k) would work.

To further verify functionality for basic logic analyzer tasks I fed low rate (11520 bps) serial data into the probe. This signal was generated by a FTDI UART. I measured the rise and fall time to be near 10ns. I repeated "hello" 100 times, triggered off of it, and counted the trigger pulses. There were 100 triggers. I followed this by inserting a 200k potentiometer. Across the entire range the scope was able to decode the signal (less reliably at 200k) which is a point where my simulation drastically departs from reality. No glitches or false triggering. This seems to be acceptable.

Every choice you could make has a tradeoff. oz2cpu's design seems pretty flexible. If you are trying to cut costs I can't find a reason why picking a different cable, using slightly different passives, or even making some changes to the layout would prevent this from working. The only way I could break it was by selecting a wildly different set of component values. The voltage divider action or at least some compensation for the reactance seems necessary for this to work properly.

[Slartibartfast]

Calling something "compatible" implies a matching of capabilities.

Not really. Unfortunately that word is far too corrupted by marketing people to mean anything like that specifically.

[gtube]

Hello oz2cpu,
Thanks a lot for your great work and sharing! I just tried to order a couple PCBs from JLC. I just noticed that POD PCB is missing in the thingiverse link below. Only scope plug in PCB is there.  Could you please upload the POD PCB?

Thank you!

ALTIUM AND GERBER FILES ARE NOW IN THE ZIP FILES HERE:

my 3D design files : https://www.thingiverse.com/thing:4784443

[gtube]

I was thinking, instead of twisting and soldering those interconnect wires between POD and PLUG IN PCBs,  how about use CAT8 shielded Ethernet cable which already has 4 twisted pairs inside? Just install two RJ45 ethernet jacks on both PCBs.

[oz2cpu]

the POD files are in the link
try to look at this file
Production_Data_SDS_1.zip

[nall]

Thanks to oz2cpu and others for this design. I finished building my set last night and it seems to be working great!

I have extra PCBs if anyone wants them for cost of shipping -- just PM me. all gone

[Coder69]

Hi,

I have started to check the Gerber-files for the plugin board. I think the board thickness should be
1.6mm and the surface finish ENIG. Especially for ENIG you can choose the gold thickness between
1 U" and 2 U". What do you you recommend ? Is 1 U" enough ?
BTW: Thanks a lot for this project ! 

[oz2cpu]

i ordered my PCB's from JLC and asked for 1.6mm
i also asked for enig, just the cheapes is fine for me,
do you expect to pull it in/out 3 times pr week, the whole year ?
then order the thicker gold :-)

[mnementh]

   

After considerable reading on eevBlog and some time in Frustion360, I've devised an alternate solution which leverages TK's adapter PCB to connect directly to the HP logic probe pods; tautech seemed to quite like the project and suggested I post in here about it, so here's the link:

https://www.eevblog.com/forum/testgear/diy-logic-probes-alternate-approach-using-tks-adapter-pcb/msg4326775/#msg4326775

Cheers!

mnem
 

[rogersstuart]

I recently purchased a 2pF active probe and compared measurements with that to a simulation using VNA measurements and an EM simulation. I found that with an FFC a value of 5.1 pF at the input of the scope leads to a nearly perfect 1/10 voltage divider. There is a little overshoot but not much ringing. The VNA measurement shows almost no ringing which leads me to believe that any ringing is simply a grounding error. The biggest variable in regard to voltage level at the scope input is how much the cable loads the signal. If you intend to use the full range of 10V then I suggest decreasing the value of the capacitor. The quality of the cable does matter but this isn't really the most high speed logic analyzer out there and you will find that the signal jitters around a bit as the specs state in the datasheet regardless of the "quality" of the cable used. 

[aystarik]

Hi,
I've desided I want my own design of the PCB for RF1.37 (https://aliexpress.ru/item/1005003601266058.html) coaxial cables (1 ground pad for each input) :   and also make it more "equal". I think I'll try to have input-end 120 ohm resistor directly on the cable, without additional boards -- like here: https://community.element14.com/technologies/test-and-measurement/b/blog/posts/building-solderable-in-circuit-oscilloscope-probes

github repo with kicad project is here: https://github.com/aystarik/siglent-la

[Wahyueko]

I want to make it for my MSO5000

[tautech]

I want to make it for my MSO5000

It has its own thread dedicated to DIY logic probes.
Use the forum search.

[Wahyueko]

yes I've tried searching, I want to try to assemble this logic probe. now I have printed the pcb to the pcb manufacturing factory.

[tautech]

yes I've tried searching, I want to try to assemble this logic probe. now I have printed the pcb to the pcb manufacturing factory.

It will not fit MSO5000.

Please go here:
https://www.eevblog.com/forum/testgear/low-cost-logic-analyzer-probe-for-rigol-mso5000-easyeda-project/

[Wahyueko]

Big thanks sir,
I used the Tektronix mso5204 logic probe which is compatible with p6616, but the price is quite expensive.
not rigol mso5000

[Wahyueko]

I have already printed the PCB, I hope you can, sir.

[rogersstuart]

I have already printed the PCB, I hope you can, sir.

Did you make it 2 layers without adding a ground pour? If so, you would need to reorder them anyway. The probe in this thread is not designed for the MSO5000. The Siglent scopes have all of the digital probe active electronics inside the scope. The MSO5000 series needs (at the bare minimum) external LVDS line drivers to work properly. Get on chat with JLCPCB and see if they can dispose of the PCBs you ordered and refund your shipping. There are multiple people on eBay selling the MSO5000 probes. Just go order one of those.