Products > Test Equipment
MS05000 Budget Logic Analyzer Probe Set Design
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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 \$\Omega\$ (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:

--- Quote from: ebclr on March 22, 2020, 01:05:50 pm ---I'm interested in a full kit including ALL components, Can you do that?

--- End quote ---
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.
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