Products > Test Equipment
MS05000 Budget Logic Analyzer Probe Set Design
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Gandalf_Sr:

--- Quote from: S. Petrukhin on December 13, 2020, 08:14:22 pm ---
--- Quote from: Gandalf_Sr on December 13, 2020, 02:00:45 am ---The Vref that comes from the scope is the one that is supposed to set the logic level but it doesn't do anything, the voltage level translators take care of that based on the VccA voltage, it's detailed in the datasheets but you don't need to worry about it, just set the VccA for the system you're probing.

--- End quote ---

Hi, Gandalf_Sr!

I checked both Vref outputs from the scope - it sets voltage to these outputs, which user selects in LA menu.
In groups for 1-8 and 9-16 LA inputs.

--- End quote ---
I know but, in my design, the Vref output from the scope is not connected to anything.  The LVDS ICs run from 3.3V and that gives the voltage that the MSO5000 expects.  The voltage level translator ICs automatically adjust the Hi Lo threshold voltage based on the value supplied to VccA,
S. Petrukhin:

--- Quote from: Gandalf_Sr on December 14, 2020, 01:00:15 pm ---
--- Quote from: S. Petrukhin on December 13, 2020, 08:14:22 pm ---
--- Quote from: Gandalf_Sr on December 13, 2020, 02:00:45 am ---The Vref that comes from the scope is the one that is supposed to set the logic level but it doesn't do anything, the voltage level translators take care of that based on the VccA voltage, it's detailed in the datasheets but you don't need to worry about it, just set the VccA for the system you're probing.

--- End quote ---

Hi, Gandalf_Sr!

I checked both Vref outputs from the scope - it sets voltage to these outputs, which user selects in LA menu.
In groups for 1-8 and 9-16 LA inputs.

--- End quote ---
I know but, in my design, the Vref output from the scope is not connected to anything.  The LVDS ICs run from 3.3V and that gives the voltage that the MSO5000 expects.  The voltage level translator ICs automatically adjust the Hi Lo threshold voltage based on the value supplied to VccA,

--- End quote ---

I reminded you just in case I didn't notice... :)
I generally find this feature strange or rarely used. If you need some special non-digital signals to explore LA, RS-232 for example, - there are 4 analog inputs.  :-BROKE
2efa4605b83bf1af48bf6736b:
I received my boards this week and put them together last night. To my surprise (due to my soldering skills), it worked! The 0603 components and fine ICs tested me out so I bought a magnifying lamp which was well worth it. Here are a few photos. I found that Vadj did not correspond with the build notes but otherwise it was all good. Thanks very much to Gandalf Sr. for his work on this.
S. Petrukhin:

--- Quote from: 2efa4605b83bf1af48bf6736b on December 19, 2020, 04:59:56 am ---I received my boards this week and put them together last night. To my surprise (due to my soldering skills), it worked! The 0603 components and fine ICs tested me out so I bought a magnifying lamp which was well worth it. Here are a few photos. I found that Vadj did not correspond with the build notes but otherwise it was all good. Thanks very much to Gandalf Sr. for his work on this.

--- End quote ---

I recommend that you use flux when soldering to avoid sharp solder tails.  :)
Gandalf_Sr:
@2efa4605b83bf1af48bf6736b

Thanks for the pictures; I LOL'd when I saw the serial decode  :-DD

Vadj is ultimately limited by the supply from the scope (nominally 4.2V) which also passes through the ferrite bead/PTC that's on the connector PCB.  If you used a PTC, that's most likely where you're losing the voltage, I prefer fitting a ferrite bead instead of the PTC.  I chose the adjustable LDO regulator on the probe PCBs because it has the lowest drop out voltage (difference between input and output voltage) I could find, that's why it's relatively expensive.

In the end, the simplest solution to the limitation of the Vadj range is to supply VccA from the circuit under test, the current pulled from the DUT will be microamps.

Anyway, I'm happy that it's working for you.

PS, I noticed that you have 2 missing pins on the 0.1" header on your probe PCB, why was that?
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