Medtronic Open Ventilator - schematic Q & A

[Clear as mud]

I downloaded the Medtronic files from https://www.medtronic.com/us-en/e/open-files.html, just for curiosity because it looks a little complicated for me to try to manufacture.

I've started looking through the POWER SUPPLY BOARD schematics, and I have a couple of questions:

1. What are the ML and PG devices?  I thought maybe inductors or filter beads, but then it doesn't make sense to have them connecting power to ground on a DC circuit.   There is an ML shown on the right side of page 1, and on the left side of page 3, on the power supply schematic.  There are two PG devices there on the left side of page 3, too.

2. Is it a mistake to not transpose RX and TX flags on the right side of page 3 where they go into the DS2480B?  They come from pins 31 and 32 on the microcontroller.  It is my understanding that RX on one chip should connect to TX on the other, not RX to RX and TX to TX.

Those are all of my questions for now.  I've been entering this schematic in KiCad, mainly as a way to familiarize myself with the new version of KiCad, and I think I'll move on to other projects unless someone might have a use for my KiCad copy of this schematic.

[awallin]

FWIW there's some ongoing effort of making kicad schematics here:
https://forum.kicad.info/t/kicad-open-ventilator-system/22084
repository here: https://gitlab.com/sethhillbrand/openventilator

[tkutscha]

Here are my educated guesses:
1. Since these are all located right near connectors, I'm thinking that they are ESD devices (like spark gaps).  The ML devices are on power supplies (beefier) and the PG devices are on the USB signals.  If a high voltage spike comes in (static shock), either plus or minus, it'll get shorted to ground instead of damaging internal circuits.

2. If you look at the datasheet for the FT2232, the ADBUS0 and BDBUS0 pins are TX, which means they go to the RX pins on the ST and PIC.  Likewise, the ADBUS1 and BDBUS1 pins are RX, so they get the TX from the ST and PIC chips.

[Clear as mud]

Well, since nobody on the project has claimed the power supply board yet, and it is the one I've been working on, I think I will join it.

Updated questions:

2. I put the wrong page number before - my question was whether TX and RX need to be swapped on the right side of page 1.

3. This is just a semantic issue, but shouldn't the MCLR label be indicated as an input where it goes into the PIC (page 1, PIC pin #7)?

4.  I've been assuming the things labeled "PST" are test points.  Is that right?

[donotdespisethesnake]

It is my understanding that RX on one chip should connect to TX on the other, not RX to RX and TX to TX.

Generally speaking, it's not that simple. The original RS232 spec has a DTE and a DCE. For the circuit TXD, it is connected TXD to TXD, and TXD is an output on the DTE, and input on the DCE. But the concept of DTE/DCE doesn't really apply in environments where it is now used.

MCU devices transmit on their TX pin, but that may not apply to other devices. In the case of a transceiver, TX is probably an input on the logic side and output on the bus side. The only way to know for sure is to check the datasheet for the device concerned.