RPL1116 (MSO1000Z) and PLA2216 (MSO5000) Active Logic Probe teardown

[dren.dk]

Well, caps on the bottom get held on with the surface tension of the solder during reflow of the top side, so there's really no reason for glue.

... unless you have very heavy components on the bottom that is.

[felix ch]

I was noticed you ordering PCB from szjlc.com and soldering it by yourself.
Szjlc provide SMT service for one side parts in chinese. Not for every single part of course, but resistors and capacitors are supported.
I'm not sure if the service is available for you.

[dren.dk]

Yeah, I assumed that they would have that service, though I admit I didn't look into it as I assumed that the startup cost would be too high for a single prototype.

I just looked around for it, but I could not find any information on how to submit such an order from the international site, so I think the assembly service is still Chinese-only.

[johnmx]

I was noticed you ordering PCB from szjlc.com and soldering it by yourself.
Szjlc provide SMT service for one side parts in chinese. Not for every single part of course, but resistors and capacitors are supported.

Those SMT services in China are cheap, but there is a catch.
You have to choose if they use their parts or you send the parts to them.
If you send the parts, the shipping cost plus the increase of customs taxes when importing the boards will make the final price too high. So it will be cheaper to assembly by my self.
If they use their parts, the circuit quality will be extremely affected. For sure they will use the cheapest and crappest ceramic capacitors they can find. Probably they will even use counterfeit ICs.

[ebclr]

What evidence do you have of this assumptions ?

[SilverSolder]

I would love an assembly service, even if it was just for the passive components.

[dren.dk]

I finally received the updated PCBs monday and yesterday we assembled two sets.

There's a photo of the frame just before going into the the oven.

We took a flir image of the board after letting it run a little and it seems the solid ground plane does it's job and is very much needed as the comparators still got up to over 60 degrees even with the copper plane spreading the heat.

Two things of note about the boards and stencil from https://jlcpcb.com/
* One via on one of the pods was disconnected, so we had to run a wire, I checked out a couple of the other boards, but did not find the same problem, so it's certainly not a design problem. Perhaps I'm pushing capabilities by using 0.3 mm via holes and would be better served with 0.4 mm drills and larger pads in future designs.
* I wanted to have alignment holes in the stencil, but for some reason jlcpcb ignored my paste gerbers and produced a stencil from the soldermask, thus handily ignoring my alignment holes that I designed into the stencil, drilling those holes was super fiddly.

I remember reading about the stencil problem, but it slipped my mind when I placed the order; aparently the way to getting the stencil you want from JLCPCB is to order the stencil separately from the PCB with only the paste gerbers in the zip file.

[dren.dk]

Note also that the scope itself gets quite toasty, I wonder what this will do for the life time.

One of my collaborators is in the process of designing a 3d printed case which will be printed with slightly conductive filament and get lightpipes for the LEDs and a bottom covered by an 1mm silicone sheet.

[TK]

In my opinion the LEDs should be removed from your design, they don't add any information to the end user and can be distracting.  They  might be useful only after assembly if you just want a visual confirmation of the rails being there, but it is adding complexity and power consumption to your design.

[dren.dk]

I see, good thing we didn't make it for you then.

Beside your personal preference, everything you said is just plain wrong:

0: If someone wanted to build one of these pods, then it would be very easy to leave out the offending parts and the space they take up was added to be able to have proper mounting holes, so there's no disadvantage to removing the option.
1: The LEDs show the current threshold voltage, so it's easy to notice if it has been set incorrectly, without digging down to the appropriate menu on the scope.
2: IOW: the LEDs do not show the power rails are there, but rather make critical information more readily available exactly where it's needed.
3: The added complexity is 2 extra BOM items (LEDs and micro controller, the resistors and the decoupling cap are the same as other items already used) in total it's 10 extra parts, the total number of parts on a pod is around 50.
4: Seeing as how the comparators dissipate enough power to reach 60 degrees, nobody is going to notice the  extra 10 mW taken by the microcontroller and a led.

Now, if I was building a mass-market product, then bean counters might force me to drop the reference-voltmeter option or start optimizing away decoupling caps, but as there is probably never going to be built in more than 5 of these sets, then cost optimization is not at all a priority.

The most important priority is that I build what I want, especially when the cost is basically zero.

[TK]

The most important priority is that I build what I want, especially when the cost is basically zero.

I was just trying to comment on your design, as you made it public on this forum.  The idea of sharing something in eevblog is to get other's opinions, right?

[TK]

I see, good thing we didn't make it for you then.

Beside your personal preference, everything you said is just plain wrong:

0: If someone wanted to build one of these pods, then it would be very easy to leave out the offending parts and the space they take up was added to be able to have proper mounting holes, so there's no disadvantage to removing the option.
1: The LEDs show the current threshold voltage, so it's easy to notice if it has been set incorrectly, without digging down to the appropriate menu on the scope.
2: IOW: the LEDs do not show the power rails are there, but rather make critical information more readily available exactly where it's needed.
3: The added complexity is 2 extra BOM items (LEDs and micro controller, the resistors and the decoupling cap are the same as other items already used) in total it's 10 extra parts, the total number of parts on a pod is around 50.
4: Seeing as how the comparators dissipate enough power to reach 60 degrees, nobody is going to notice the  extra 10 mW taken by the microcontroller and a led.

Now, if I was building a mass-market product, then bean counters might force me to drop the reference-voltmeter option or start optimizing away decoupling caps, but as there is probably never going to be built in more than 5 of these sets, then cost optimization is not at all a priority.

The most important priority is that I build what I want, especially when the cost is basically zero.

Your eyes will be 90% looking at the scope anyways and not trying to look at some LEDs blinking on a sea of wires.  At least that is my experience debugging logic circuits.

[dren.dk]

That's fair, I probably ended up sounding much more argumentative than I wanted, sorry if that was the case.

The point of the leds is not to blink out information, but to make it clear what the threshold is set at when I'm hooking up the probe, which is especially important and easy to miss if both pods are in use as the two groups of inputs have separate threshold voltages.

The state of the leds only change when changing the threshold voltage, so there should not be any need to stare at them or to get distracted.

[TK]

Good points about the LEDs and the threshold settings

[oliv3r]

just make sure the leds are dimm enough to not be a distraction; using large resistors to reduce the current to 5mA may be just the solution Personally, I like the idea of the LEDS

[dren.dk]

Don't worry about the LED brightness I'm very annoyed by overly bright LEDs myself.

The LEDs used are these ones: https://datasheet.lcsc.com/szlcsc/Lite-On-LTST-C193TGKT-5A_C12065.pdf

From the datasheet we get a forward voltage of about 2.5-3.1 V, so let's call that 2.8 V and a max current of 20 mA.
The supply to the MCU is the -2.3/2.5 V rails, so that's 4.8 V in total.

I designed with 2x 220 Ohm resistors for a peak current of (4.8V-2.8V) / 440 Ohm = 4.5 mA.

I'm running the LEDs with a fixed rate charlieplex where each LED gets one out of ten PWM periods, so that means that the average current at 100% PWM is 0.45 mA per LED.

As I'm not a fan of bright LEDs I've turned down the PWM to 1/255, which yields an average current of 2 uA

The initial result was too bright, so I upped the resistors to 2x500 Ohm for a peak current of 2 mA and that seems about the right brightness.

I must say I'm very surprised about how much light is yielded by the charlieplexed LEDs even at a crazy low peak current.

We assembled serial number 3 last night, here's the recipient of #3 stuffing 0402 10 nF decoupling caps and swearing a lot.

#3 ended up working perfectly.

The recipient of #2 is in the process of printing cases for us.

The firmware for the voltmeter is also working perfectly, so after calibration the exact threshold voltage is reflected by the LEDs.

[Sprite_tm]

As a warning for other people that try to DIY this using an LMH7324: there are fakes of this chip on the Chinese market, as I can unfortunately tell you from experience... I built my pod, and 8 of the 16 channels refused to do anything. Luckily, I own an advanced device for looking inside of chip packages to debug this issue... Seems they forgot to put the actual silicon into half my chips, grmbl. FYI, these come from Taobao; that was the easiest source I could get them from seeing as I live in mainland China.

Images (click to embiggen):

[pmnxis]

I ordered PCB and parts with following this thread.

Thanks. I will try to assembly and test on my new mso5000.

in my case I spent 150usd more for parts and pcb. but it's interesting and cheaper than pla2216.

BTW I changed some connector and cable assembly for rapid works (there's no stock for connector, so changed little bit)

And I don't have experience about making IDC 1.27 cable by hand. so ordered already made one.

[thmjpr]

Started on the USB C probe idea from Muza giving 4 signals per probe pod, 4 pods total. Schematic is basically straight copy of dren.dk then the connectors were changed out.

Main connector: https://www.digikey.ca/product-detail/en/sullins-connector-solutions/SFH11-PBPC-D25-ST-BK/S9201-ND/1990094 $3
Type C connectors: https://lcsc.com/product-detail/USB-Connectors_Jing-Extension-of-the-Electronic-Co-LCSC-USB-3-1-C-TYPE-DIP-SMTFemale-10-0L-High-temperature_C168698.html $0.50

Board is 1.6mm, ideally would be 2mm to match the header connector pin spacing but JLC just has their cheap impedance controlled board in 1.6 (JLC7628).

In retrospect, HDMI is a much better solution in almost all aspects: you don't have the polarity issue, and proper spec cables are easier to find. Probably why we've seen HDMI on siglent scopes and on CC payment terminals, etc. But, once you realize the quirks of USB-C its not too bad, its just that there are sooo many of them. Most cables wouldn't work, flipping the cable will of course screw up your channels (if you want to be lazy you can simply mark the "up" end on your cables), and active cables won't pass through our signal or could blow from the voltages we are using.

For finding the right USB cable, what you want is a passive "super high speed" or "USB 3.1 gen 2" or "10Gbps". These, if correct, indicate that all four high speed pairs are wired inside the cable. I bought two cables and it looks like they both are suitable (very surprising given how cheap they were, about 19 wires! need to be run and cables are hand assembled for the most part). They have the labeling: "VW-1 type 2725", unsure what it refers to (related).

Cable 1: https://www.aliexpress.com/item/30cm-USB-C-USB-3-1-Type-C-Male-Connector-to-Male-Data-Cable-for-Tablet/32825241462.html $3
Cable 2: https://www.aliexpress.com/item/USB-Type-C-Cable-USB-3-1-Gen2-USB-C-Male-to-Male-Data-Sync-and/32893896190.html $6

First cable is way too short (30cm), I bought it thinking it would be fake/mislabeled, but its not, has all the right pins wired up.
Second cable appears to be very high quality, again same internal wiring. Of course I can't tell the power cable diameter inside or bandwidth of the HS pairs, so quality is purely based on physical feel.

Neither of these cables seem to have the internal 1k pull-down resistor on CC2 line, which I was expecting. Also, all multi-pin connections VBUS/Gnd/etc. are connected internally on the cables. Knowing these two things would have made layout a bit simpler. Shield is internally connected to Gnd as well, no messing around with having that connected in some strange way.
For the CC2 line, basically there are two polarity detection lines, CC1 and CC2. One is connected through the cable and one is not. So based on where that pin ends up, you can determine which one of the four orientations the cable is in.

[gizmo5418]

Hi,

I want to thank you for this great LA project. I successfully made LA to MSO5000. All channels work, but channels 1, 3, 5, 7, 9, 13, 14, 15 have a negated level, as in the screenshot of the MSO5000. Voltages -2.5V, + 2.5V, + 4V, Vref1, Vref2 are correct. I noticed the same negation of channels in the user's picture dren.dk.
It seems to me that the signals of negated channels in the LA project are reversed - one should introduce a correction on the PCB Breakout..

I am sorry for my English, I use a Google translator.

Regards,
Pawel

[pmnxis]

also i had same issue.

[dren.dk]

Sorry, I fell off the project and just came back to the thread, cool to see that people have actually built the boards!

I just did a basic smoke test and put the project on the shelf, so I never noticed that some channels were inverted, what an embarrassing mistake to make.

I wonder where the error was made, I guess I'll have to do some measuring to figure out where the signal is swapped, but the only way it could be someone elses fault than mine is if it's the pinout I used for the scope.

The best solution would be to redo the breakout board, but it ought to be possible to swap the affected pairs in the cable and put the connector back on.

[pmnxis]

Thanks for comeback and your participation for made them!.

There's another issue that some channel cannot change state or mixed remarkable noise.
I cannot sure mine was broken while connect cable with wrong angle with short time.
or cable or assemble is strange.
I will try to figure out what was problem
I hope there's no problem on my scope

BTW are there any people have same noise issue like me?

[gizmo5418]

Hi,

I have noise if I have a "PCB Breakout" attached without connected logic probes.

pmnxis, connecting the ISP programmer at the same time that LA was connected to the oscilloscope was probably not the right solution.
Preservation of my oscilloscope with "PCB Breakout" plugged in without logic probes:

[pmnxis]

thanks for you pictures.
Mine got some "too much" noisy issue on 6th channel when didn't connect cable 0to7 channel.
BTW I solved issue that channel 1ch(start from zero) didn't work.
I was soldering each only one point to 2 bypass capacitor near the MCU.
and re-soldered array capacitor. and then it works.

for now, a left issue is a known issue. some channel is inverted.
hope it would be nice fix later. but I think that's not immediately to me and enough for see extra point for change or triggering something.