Author Topic: MS05000 Budget Logic Analyzer Probe Set Design (Read 54572 times)

lodkolven · « **Reply #50 on:** March 25, 2020, 01:54:14 pm »

Perhaps take the 5v supply from the USB-port on the MSO5000 ?

Gandalf_Sr · « **Reply #51 on:** March 25, 2020, 01:56:54 pm »

Quote from: lodkolven on March 25, 2020, 01:54:14 pm

Perhaps take the 5v supply from the USB-port on the MSO5000 ?

Quite a good idea. I'll add it to suggestions for V2.

free_electron · « **Reply #52 on:** March 25, 2020, 03:29:51 pm »

many level translating buffers do not like it when one of their sides is left unpowered.
last time i made a 'universal input' probe i used a simple opamp with strong output drive capability to power the input side.

essentially put an opamp like a TS921 or TS951 ( that can drive 40 or more milliamp on its output) in unity gain. the output feeds the power rail of the level shifter
the input of the opamp is protected with tvs diodes and sent to the IO_SENSE pin of your probe.
a 1 meg resistor comes from your internal 5 volt rail to the opamp input as well.

So : if you do not attach anything to the SENSE line the level shifter gets 5 volt ( the opamp sees 5 volts through the 1 meg resistor )
if you wire the SENSE line to the power rail of the circuit under test the opamp will simply follow that rail voltage , so the level shifter gets the voltage of the circuit under test.

Gandalf_Sr · « **Reply #53 on:** March 25, 2020, 03:39:20 pm »

I like the 1Meg resistor to a 5V power rail idea (except there is no 5V power rail - but I could steal one from the USB connector) idea but the datasheets for these voltage level translators (VLT) specifically say that, if either Vcca or Vccb goes below a specific voltage, they go into disabled high-impedance mode. In my latest Probe PCB revision vn1b3, the one that's being manufactured right now, there's provision for a 100k resistor from Vcca to ground to specifically disable the VLT if there's no Vcca voltage applied.

Again, good ideas for revision 2 but I guess people can easily modify vn 1b3 if they want to try that out.

Gandalf_Sr · « **Reply #54 on:** March 25, 2020, 05:35:59 pm »

Here's a 3D printable Probe PCB protective back I designed today. Enjoy

Gandalf_Sr · « **Reply #55 on:** March 25, 2020, 07:36:31 pm »

Here's a photo of two Probe PCBs fitted with the 3D-printed protective back. It snaps on and protects the underside from shorts.

Gandalf_Sr · « **Reply #56 on:** March 30, 2020, 03:42:53 pm »

Both PCBs are now at 94% on some mystery step 16... Looks likely they will ship soon.

[EDIT] They shipped today (3/31/20) and are scheduled to arrive Monday April 6th.

Gandalf_Sr · « **Reply #57 on:** April 02, 2020, 03:10:48 pm »

Update...

The PCBs shipped REALLY fast by DHL, they are on the truck for delivery to me by 8pm today April 2nd!

Still have plenty of spare if anyone wants a set.

Gandalf_Sr · « **Reply #58 on:** April 05, 2020, 04:30:26 pm »

Update. I got the new ENIG PCBs from JLC and they look great.

I wanted to make sure all was well before I shipped PCBs out so I made up a 5V Probe PCB with all the changes (10k parallel resistors, 100k pulldown on Vcca, protection Zener on 3.3V rail) and a new Connector PCB and tested at 50 MHz, all seems fine. Here's a couple of pictures. You'll see that the new Probe PCBs have a little white silk screen rectangle to write the voltage version on.

Given the state of the lock-down, I didn't want to go to the Post Office so I ordered Priority Mail padded envelopes from USPS (free) but they haven't arrived yet; as soon as they do I will ship out to those who have PMd me (and paid).

[EDIT] If you're building a set and are looking at my pictures below, be aware that the connector PCB is sitting face down in the picture of the 3 PCBs - pin 1 of the 24 pin connectors that take the headers for the ribbon cables has a square surround so, as you can see, if the Connector (top) board was flipped over left-to-right, the square pin 1 would be bottom right, matching the 24 pin headers on the Probe PCBs.

Gandalf_Sr · « **Reply #59 on:** April 06, 2020, 11:27:00 pm »

People who've sent me money were sent PCBs today by Priority mail, 2 or 3 days to get there depending on how far away from Michigan you are.

I'm going to try to figure out how to send overseas in small envelopes; bear with me.

Gandalf_Sr · « **Reply #60 on:** April 07, 2020, 02:41:51 pm »

Here's an updated (vn2) set of build notes.

[EDIT] OK, who spotted my (ahem) deliberate typo in that I run my soldering iron at 28 degrees C? It should be 280 C.

Gandalf_Sr · « **Reply #61 on:** April 10, 2020, 04:40:29 pm »

bigboss59

I am trying to send you PMs but it tells me your inbox is full. FYI, I can ship to France.

For others, I have figured out how to send to France, Sweden, Portugal, UK, Australia for a reasonable rate (with no tracking or insurance) so I can send PCBs for the prices I already stated.

The USPS web site lists countries that they will not ship to at the moment but the above are not on that list.

PM me if you're still wanting PCBs.

Gandalf_Sr · « **Reply #62 on:** April 11, 2020, 01:39:05 pm »

Some of you will be getting the bare boards soon, here's a few notes on the circuit that may come in useful...

Connector PCB
Align J1 before soldering then solder just 1 pin and check it's straight. IF IT ISN'T STRAIGHT, DO NOT TRY TO BEND IT STRAIGHT or you will lift the pad. Heat the 1 soldered leg and realign. Once it's aligned properly, solder the other legs.

Probe PCB
Be careful fitting VR1. I over-temped one and it was damaged and gave lumpy control of Vadj. Best practice is to turn VR1 upside down and tin the bottom of the leads; then tin the 3 pads on the PCB and carefully sweat it down 1 leg at a time.

Protection circuits.
PTC on the Connector PCB
There's a positive temperature coefficient (PTC) device on the bottom side of the connector PCB. The Probe boards draw all their power from the +4.1V supply via the PTC but PTCs have a fairly high resistance and using one will limit how much current you can draw from the downstream +3.3V (300 mA max limit of the LDO per Probe PCB) and Vadj (100 mA max limit of the Vadj LDO per Probe PCB) supplies - so, in theory, you could draw 800 mA total from the MSO5000 which you would never achieve using a PTC. Also, I don't know what the current limit is that can be supplied by the MSO5000 4.1V line; the PTC will limit total current to under 500 mA. However, if you put the listed ferrite bead on the connector PCB in place of the PTC, you will get whatever the MSO5000 can supply. I've tested that the LA works with both a PTC and a ferrite bead but I haven't done limit tests yet.

Probe PCB Overvoltage Protection
D2 is a 3.9V Zener on the 3.3V rail, if the 3.3V rail is taken above around 3.6 volts (should never happen) this Zener will ground the 3.3V supply.
D3 is a 3.9V Zener connected to the Vext pin via R8, a 47.7 Ohm 0.25 Watt resistor. If you're building the 5V version, D3 is a 5.6V Zener and may trip as low as 5.3 volts which may cause issues if you're using an over-voltage 5V logic input at say 5.2V (check the range in the diode's datasheet). If this is a problem, you can either put a higher voltage Zener as D3 or leave D3 off the PCB and have no protection other than the 47.7 Ohm resistor. If you want to supply the device under test with more than a few mA of current and you're using Vext to supply the DUT, be aware that R8 will reduce the supplied voltage; however, you can supply the device under test from the Vadj or +3.3V pins (device shutdown limits are 100 mA or 300 mA) on the 3-pin header just above the switch.

R21 (100k Ohms)
R21 is provided to pull Vcca down to zero when there's no power. I found that Vcca would stay on for seconds at a time without R21, probably because the voltage level translator (VLT) IC draws so little current. The ACX (3.3V) version of U1, the VLT, is most susceptible to this effect although it's not really an issue, I just didn't expect U1 to operate with no Vcca supplied.

NoisyBoy · « **Reply #63 on:** April 12, 2020, 02:25:57 am »

Hey Gandalf_Sr,

I have been watching your project since your inception during your cruise, but I did not have time to participate. Nice work and that was done really fast! Great work and thank you for all your kind contribution to the community. I am many here will benefit from it without having to pay the high price for the Rigol probe.

Gandalf_Sr · « **Reply #64 on:** April 12, 2020, 09:50:02 pm »

Thanks, that last cruise was just in the nick of time before the whole shut down kicked in. I'm still getting requests for PCBs.

ForceFed · « **Reply #65 on:** April 13, 2020, 03:44:44 am »

PCBs and Digi-Key order have arrived. Thank you again!

Gandalf_Sr · « **Reply #66 on:** April 13, 2020, 09:21:04 am »

ForceFed and others,

Ask here (or send me a PM) if you run into any problems, I think the design is good but I'm not infallible.

Gandalf_Sr · « **Reply #67 on:** April 13, 2020, 10:37:36 pm »

bigboss59 keeps PMing me asking if I got his PMs. His mailbox is full and I can't send him replies, if someone can contact him and tell him that, I would appreciate it.

Gandalf_Sr · « **Reply #68 on:** April 15, 2020, 10:46:30 am »

Apologies to those non-US people who've paid me for the PCBs; I haven't shipped them yet because the $1 stamps I ordered a week ago from the US Postal Service STILL haven't arrived and their stupid rules won't let me use the click-n-ship system to print postage from my PC system for overseas mail. I will see if I can talk my wife into allowing me out to the Post Office to buy them over the counter.

TK · « **Reply #69 on:** April 15, 2020, 01:34:36 pm »

If you have paypal account, you can use it to print postage domestic and international http://paypal.com/shipnow

Gandalf_Sr · « **Reply #70 on:** April 15, 2020, 02:26:03 pm »

Quote from: TK on April 15, 2020, 01:34:36 pm

If you have paypal account, you can use it to print postage domestic and international http://paypal.com/shipnow

Thanks, but not for the photo-mailers that I need to use to get under the wire for non-exorbitant mail charges.

TK · « **Reply #71 on:** April 15, 2020, 05:45:47 pm »

You can ship flat padded envelopes to Europe for around $4 to $5 using paypal shipnow

Gandalf_Sr · « **Reply #72 on:** April 15, 2020, 07:31:57 pm »

Quote from: TK on April 15, 2020, 05:45:47 pm

You can ship flat padded envelopes to Europe for around $4 to $5 using paypal shipnow

I tried to do that today, my PayPal account seems to be broken, it won't let me quote for a flat rate envelope as it says I have no credit cards associated with my account (I do), I tored to call customer service; after going through their menu system, I got a message saying that due to Corona virus, their customer support is closed and then hung up on me.

Mail man has been, no stamps. Fuck it I'm going to the Post Office.

TK · « **Reply #73 on:** April 15, 2020, 07:52:44 pm »

Sorry to hear it is not working, I used it last week and was OK.

Gandalf_Sr · « **Reply #74 on:** April 15, 2020, 08:09:43 pm »

Quote from: TK on April 15, 2020, 07:52:44 pm

Sorry to hear it is not working, I used it last week and was OK.

No problem and no need to apologize, I know you're only trying to help; it's just so frustrating that I can't do something as basic as buy stamps or postage and every basic service organization has no customer support operating, I tried to call USPS to say "USPS yer c****s, where's me f###ing stamps?" (plagiarized from Kevin bloody Wilson) but they too had a message saying that, due to Corona Virus, they have no customer support operating.

Wife got upset when I said I was going to the Post Office and put her foot down with a firm hand. I'm just going to stick umpteen Santa 'forever' stamps on each package, they're supposed to be worth 55 cents each.


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Author Topic: MS05000 Budget Logic Analyzer Probe Set Design (Read 54572 times)

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