MS05000 Budget Logic Analyzer Probe Set Design

[electricMN]

How about option 1 but just offer the board blanks for sale if someone wants to assemble the boards themselves.

[thmjpr]

AZ23C3V6 seems to have a capacitance in the ~100pF range, which is not too high but definitely much lower capacitance diodes are available.

Its hard for me to see why you wouldn't want the high value pulldown resistors. If the pins are floating in the air and reading 0V thats one thing, but what if you are probing a broken trace or similar? It could give misleading levels if its not lightly loaded.

Input clamp current is stated as 50mA max, so if you can stay under that it would be good. 5V -> 200R -> (3.3V + 0.6V) = 6mA, seems alright.
You might consider a 3.3V TVS on the supply rail so the ICs ESD diodes have something to dump to (I'm assuming here they are present, but datasheet only mentioned Vi < 0 so not sure). If the individual line zeners are not used. I know I've said it before, but I fully expect 5V to be applied on those inputs.

[Gandalf_Sr]

I'm struggling to pick the right voltage for a TVS diode to protect the 3.3V supply rail (Vccb).  I found the PESD4V0Y1BSF but, although the min breakdown voltage is 4.2V, the typical is 6.2V, and the max is 8V.

Any comments on what a suitable TVS diode should be?

[MarkL]

...
One thing I haven't found yet is where in the menus I can align the analog and digital signals in time - I thought that was somewhere in the menus?

I don't have this scope, but according to the User Manual it's in the channel menu.  Their example for Channel 1:

Press 1 --> More --> Ch-Ch Skew, rotate the multifunction knob or use the numeric keypad to set the desired delay calibration time. The available range of the delay calibration time is from -100 ns to 100 ns.

[Gandalf_Sr]

OK, I'm close to ready to order the new PCBs although the Connector PCB is unchanged.  Attached are new pictures and I'll follow up with another post with the BOM and schematics for both PCBs.

I took out the pesky protection diodes on the input lines and placed new 10k resistors to ground on each input line.

[EDIT] I added a protection diode on the 3.3V side of the voltage level translator as requested.

I have 4 people who've asked me for PCBs, tv84, lodkolven, and electricMN - you guys will each need a Connector PCB but let me know if you want something different from the basic just 2 probe PCBs; you will need 2 to have 16 channels and you may want 3 so you can have 2 x 3.3V versions and 1 x 5.5V version.  Let me know by PM.  To cover my costs is going to be something like $20 for 3 PCBs including shipping - have ordered extras to cover the inevitable late-comers.

[Gandalf_Sr]

BOM and schematics attached in zip file

[EDIT] If anyone wants changes, speak now or forever hold your peace.

[Gandalf_Sr]

I have decided that I will define a PCB set as 1 Connector PCB and 3 Probe PCBs and I will order them in that ratio 1:3

You can still add extras but the main idea is that, if you mainly work on low voltage stuff, you can make 2 x 3.3V Probe PCBs and 1 x 5.5V Probe PCB.  Remember that any Probe PCB can be connected to either of the 24 pin headers on the Connector PCB as the 8 channel signals coming out of the Probe PCB are the same i.e. 8 pairs of 3.3V LVDS.

The 3.3V Probe PCB can handle any logic voltage level between 0.65V and 3.6V, the 5V Probe PCB can handle any voltage between 1.6V and 5.5V but, if you want to run a 5V Probe PCB at >3.9V, e.g. 5V, you will need to feed the logic voltage into the Vext pin and set the switch to Vext; the current drawn from Vext is almost zero i.e. low single digits uA.

There are only 3 components different on a 5V Probe PCB and they are all detailed in the schematic and BOM attached a couple of posts above.

[Gandalf_Sr]

I'm going to make 2 small changes to the probe PCB before ordering...

1. The test point marked Vref that is fed by J2 pin 1 does not carry Vref from the Connector PCB (which I was originally intending to do), it's just ground so its incorrect to label it 'Vref'.  I think it would be useful to have a +3.3V test point (the output from U4) which is capable of supplying 0.3A or the limits of the MSO5000 4.1V supply - a kind of fixed +3.3V mini power supply.  So the test pin marked 'Vref' will change to '+3.3V' and J2 pin 1 will be connected to the ground plane.

2. I'm going to add a do-not-populate resistor from Vcca of U3 to ground; I've found that U3 mysteriously seems to operate even when the switch is set to Vext and there is no Vext connected!  I suspect that this is because the switch is cheap and has an open resistance of maybe 1M (I've tested it) and the AXC version of U3 draws so little current from Vcca (1uA ish) that it gets enough via the open switch to operate!  My design intent was to use the feature of U3 that, if either Vcca or Vccb is <0.6V, the IC goes into disabled, high impedance mode so a 100k resistor from Vcca to ground should cure this issue even though it would draw an additional current of approx 10 uA.

Any other ideas or requests?  Need them PDQ guys.

[ebclr]

I'm interested in a full kit including ALL components, Can you do that?

[Gandalf_Sr]

I'm interested in a full kit including ALL components, Can you do that?

Not really, I could but it would be way more work for me than it's worth.  I had thought about the major components, ICs, connectors, and ribbon cables, so there could be at least the economy of buying 10s instead of 1s but I don't want to be messing around putting 3 x 0.1uF 0603 capacitors in a marked bag on their own.

[Gandalf_Sr]

About to place the PCB order, here's the (slightly) updated probe PCB

[joeyjoejoe]

Not really, I could but it would be way more work for me than it's worth.  I had thought about the major components, ICs, connectors, and ribbon cables, so there could be at least the economy of buying 10s instead of 1s but I don't want to be messing around putting 3 x 0.1uF 0603 capacitors in a marked bag on their own.

For a while, with megadesk (https://github.com/gcormier/megadesk) I would use masking tape to tape the components to a piece of paper that had the values printed out. But these were 1206. Resistors would all be together since you can read the values, but caps would be taped separately with their own text/header.

In the end, now people are only ordering fully assembled boards, I think I've probably only sent 5-10 kit orders. I still have the listing up for parts-kits but I might just take it down, as I always try to have 5 sets of loose parts on hand which is just a waste.

I think if you offer all but the jelly beans parts in a kit, that might still have some value - anyone building this for an above entry level scope should be comfortable ordering the jellybean parts from wherever

[Gandalf_Sr]

I'm setting up a BOM in the Digikey system for all the parts needed, I think there's a way to allow people to order the BOM, I will check with Digikey tomorrow.

I ordered 100 Connector PCBs and 300 Probe PCBs and made them all blue and ENIG (Electro-plated Nickel Gold) finish as it was not much more, it never goes bad, and it's much easier to solder.  It's also EU compliant as far as ROHS is concerned. Also, because ENIG is going to be put in with higher-end orders, I've noticed that the finish tends to be better e.g. legibility of the silk screen.

[electricMN]

I'm setting up a BOM in the Digikey system for all the parts needed, I think there's a way to allow people to order the BOM, I will check with Digikey tomorrow.

....

You can put all of the items in a cart and share the cart with anyone via a link to the cart. When I was still working I did this all of the time. Fill up the cart with the parts needed and send the link to the buyer. It worked out really well for both of us.

[Gandalf_Sr]

OK, here are some Digikey cart share links. These DO NOT INCLUDE THE PCBs NOR DO I GET ANY MONEY FROM DIGIKEY.

1. Share for the parts to build 1 Connector board.

Notes: this cart includes the ribbon cables and has some choices that you need to address...

There is a PTC for P1 which should work fine but, if you want to load the 3.3V supply much (>150 mA), you should consider the ALT P1 part instead which is a ferrite bead.  BOTH are in the cart. They are not much money so you can leave both in the cart or just delete the one you don't want.

You need to pick whether you want 6" or 18" ribbon cables, BOTH are in the cart.  I've only used the 6" ones so far in my testing and they are the ones in the pictures.

2. Share for the parts to build 1 x 3.3V Probe board [Edited] There were 2 U5's in cart, now fixed

3. Share for the parts to build 1 x 5.0V Probe board [Edited] Two U5's and D1 now Red, R12 330R

I think that what you will have to do is create multiple carts and then go to their combine cart feature (Google it).

Remember you will need 1 set of parts for the Connector PCB and a Probe set for each Probe PCB; you need to choose what voltage you want each Probe PCB to be, 3.3V or 5.0V.  I made the 0603 LED Green/Red for the 3.3V/5.0V probe PCBs and this is reflected in the Probe cart links plus R12 is 270/330 .

The designation of the components will be printed on the bags you receive e.g "J1,J2", if it's prefixed by "CONN_" it's a part for the connector PCB eg "CONN_J1"

Let me know if it's broken or something is missing or wrong.

[Gandalf_Sr]

I have ordered some spare PCBs so, even if you didn't contact me before, PM me and tell me what you need.  I'm suggesting $20 to cover costs plus shipping and handling for one set which I define as... 1 x Connector PCB and 3 x Probe PCBs (so you could build 2 x 3.3V probe PCBs and 1 x 5.0V probe PCB - the PCB is the same for both voltage variants).

I also ordered enough components to build 5 Connector PCBs, 8 x 3.3V PCBs, and 2 x 5.5V PCBs and I may build some up because, well, Coronavirus lockdown.

[Gandalf_Sr]

Here's an update.

The PCBs are in production now, the 4-layer Connector PCB is stated as 8 days to build (the Probe PCB is 6 days) and I paid for DHL shipping so I'm estimating April 6 for the boards to arrive with me.  They are blue soldermask with white silkscreen and ENIG (gold plated) finish - i.e. lead free.

Both the Connector and Probe PCB have a few components on the underside.  This was done with the assumption that they would be hand-built so apologies to those intending to make solder screens.  The Connector PCB has 1 x 1210 component on the underside and the Probe PCB has about 9 resistors and 1 capacitor, all 0603, on the underside.  I think it would compromise signal integrity if I tried to put all components on one side for the boards; I have tried hard to have signal lines running with nothing but a clean ground plane on the next adjacent layer.

I will do a full write up on hand-assembly with tips.

[Gandalf_Sr]

OK, I'm getting multiple requests for PCBs via PM which is fine but I need to clarify and simplify things for you guys and me.

There's only 1 Probe PCB design, you put slightly different components on it (e.g. an LVC voltage level translator) to make it into a 5.5V version vs a 3.3V version.  The voltage range that each version will handle is as follows:

3.3V version handles logic Vcc voltages of 0.65V to 3.6V (absolute maximum Vcc is 3.6V and a '1' can be Vcc+0.2V max)
5.5V version handles logic Vcc voltages of 1.65V to 5.5V (absolute maximum Vcc is 6.5V and a '1' can be Vcc+0.5V max)

There is only 1 Connector PCB design; it has no active components but is 4-layer to handle the LVDS signals as well as possible

To have a complete setup to analyze 16 channels you would need 1 x Connector PCB and 2 x Probe PCBs, these are bare PCBs and you will need to buy and solder the components to them (see post above with Digikey cart links). You also need ribbon cables to connect the Probe boards to the Connector PCB and these are included in the BOM/cart link for the Connector PCB (note 2 x 6 inch and 2 x 18 inch cables are in the BOM, unless you want both, you should remove one pair to save cost).

So I've been asked for various combinations of PCBs so I need to set some standards... I have defined a 'SET' as 1 Connector PCB and 3 Probe PCBs - Why 3 you ask?  Because, if you mainly work with 3.3V and low voltage logic, you could build 2 x 3.3V Probe PCBs and be able to run 16 channels at low voltages e.g. 1V plus you could build 1 x 5.5V Probe PCB and mix that in when you wanted to analyze 5.5V logic.  If you really want to, you can build 2 x 3.3V and 2 x 5.5V Probe PCBs giving you the ability to analyze 16 channels at any voltage within specification so I have defined a SET+1 which is 1 x Connector PCB and 4 x Probe PCBs but, for most people, I suspect that 3 Probe PCBs is fine.

So here's what you can ask me for...
A SET =  1 x Connector PCB (the one that plugs into the scope) 3 x Probe PCBs (the ones that have all the ICs on them)
A SET+1 = a SET + 1 extra Probe PCB

I am not trying to make a business out of this, it's a sort of Covid-19 project that killed time for me (lots of time) and I'm already $100s out of pocket with orders for prototypes, shipping, components etc.

I will sell a SET for $20US shipped to the USA. I will sell a SET+1 for $25US shipped to the USA.  You can also buy the following multiples:
Two SETs
Two SET+1s
One SET and one SET+1

And I will reduce cost by $7US for the combined shipping e.g. two SETs will be $20+$20-$7=$33.  If you want more/different than these offerings, please PM me and I will try to help.

I will ship overseas but it will be the actual cost of shipping + cost of PCB sets required and, if there's no tracking, it will be sent at your risk.  In the US I will use Priority Mail which come with a standard $50 insurance coverage.

PM me what you want and I will respond with cost estimate and PayPal info.  I do not expect to receive the PCBs from the manufacturers until around April 6th.

[Gandalf_Sr]

I spotted errors in the Probe PCB Digikey saved carts which I've corrected in the previous link, the biggest error is that there were 2 x U5s LDOs.  The LT3060 is expensive but it's one of the few LDOs I could find that went down to 0.6V output.

Some here have asked for the stencil files for the new PCBs so they are attached below.

[electricMN]

I spotted errors in the Probe PCB Digikey saved carts which I've corrected in the previous link, the biggest error is that there were 2 x U5s LDOs.  The LT3060 is expensive but it's one of the few LDOs I could find that went down to 0.6V output.

Some here have asked for the stencil files for the new PCBs so they are attached below.

Shouldn't item 6 in the connector board cart be a right angle connector? I believe this is the connector that plugs into the MSO5000 LA port. Or am I mistaken?

[Gandalf_Sr]

I spotted errors in the Probe PCB Digikey saved carts which I've corrected in the previous link, the biggest error is that there were 2 x U5s LDOs.  The LT3060 is expensive but it's one of the few LDOs I could find that went down to 0.6V output.

Some here have asked for the stencil files for the new PCBs so they are attached below.

Shouldn't item 6 in the connector board cart be a right angle connector? I believe this is the connector that plugs into the MSO5000 LA port. Or am I mistaken?

No the part specified is correct.  It fits like the pictures show, you have to bend the pins towards each other very slightly.

[TK]

you can specify a different thickness of the PCB before ordering to match the separation of the pins to avoid bending them and have a tighter fit.

[Gandalf_Sr]

you can specify a different thickness of the PCB before ordering to match the separation of the pins to avoid bending them and have a tighter fit.

Thanks but the PCB would have to be 2mm thick, just 0.4 mm more so the pins only need to be bent down 0.2mm per side.  As you can see from the pictures, it's not really even noticeable and has been tested at 50 MHz.  I just used a ruler to bend the pins in ever so slightly.

I suspect that would be doable if I was ordering 1,000s but I wasn't - plus my impedance calculations were based on the standard stackup for a 1.6 mm thick 4-layer PCB.

[Gandalf_Sr]

Both boards are in production and show progress

Attached is my first cut at the build notes.

Newer V2 build notes are here

[Gandalf_Sr]

Status update.

The 4-layer Connector PCBs are showing 12% completion.
The 2-layer Probe PCBs are showing 60% completion, they are at the ENIG stage.

I'm writing a user guide for a running system.

I'm considering a 3D-printable CAD design for a small plastic shield that will clip to the underside of the Probe PCB so they don't short against each other when there are 2 plugged in side by side; I might also do one for the connector PCB.

I've been checking some things too.  The absolute maximum Vcca or Vccb that the 3.3V version (AXC chip) will take is 4.2V and the Vadj should never exceed 3.9 so that looks pretty safe.

Also I've been giving some thought on 3.3V vs 5.0V versions of the Probe PCB; which one should you build?
If you think you will never want to test logic at less than 1.6 volts but want to test 5.0V stuff then you should build the 5.0V version of the Probe PCBs.
If you think you will want to test logic at less than 1.6 volts then you should build the 3.3V version of the Probe PCBs but probably build a 5.0V version too - both can handle 1.6V - 3.3V which is 99% of what I do.
On paper, the 3.3V (AXC) voltage level translator can go up to 200 MHz but the 5.0V (LVC) is limited to 50 MHz (I tested it yesterday and it works fine at 50 MHz).
A small downside of my 5.0V design is that the vn1b3 Probe PCB can't supply more than 3.9V to the board under test so a 5.0V logic board has to feed Vcc into the Vext pin of the logic header - this isn't really that big a deal and the current consumed by this pin is almost zero (a couple of uAs) so it's more a voltage reference than a supply. This could be 'fixed' by adding a small step-up regulator but I think that's taking things too far.