Electrical Engineering Change Notes

Revision 0.1

Description

First revision

Manufactured

Boards ordered from Aisler on August 15th 2022. Sent directly the Kicad files. See r0.1/ directory.

Issues noticed

• Missing I2C pull-ups on the isolated side.

• The pinout for the external RJ45 is completely wrong.

• The 1k across 12V dissipates 144 mW. It's above the rating for the jelly-bean 0603 resistors I originally used and it also gets quite warm.

• The 120R termination resistors also can dissipate quite a bit of power. Technicaly up to 6V across leading to 300 mW ! In our case, it's more like 3V so it's only 75 mW but still, some margin would be nice.

• The linear 5V reg does heat up a bit. Nothing critical, but could be improved.

Notes

• All boards have been reworked to fix most pressing issues :

  • 3k3 pullups added on the isolated side.
  • Cut & manually rewired the external RJ45 pinout.
  • 1k across 12V switched to high power 250mW part.
  • 120R termination switched to high power 250mW part.

• Boards location:

  • One remained with tnt.
  • Two sent to LaF0rge. One will be installed in the datacenter to be used with the OCTOI hub, the other will remain for testing.

Revision 0.2

Description

Potential future version, if ever done ...

TODO

• Add I2C pull ups on the isolated side.

• Fix the external RJ45 pinout.

• Use switchmode converter for supply. AP3211 looks like a good candidate.

• Replace the 1k resistor across 12V with a resistor + zener + depletion n-mos so that it appears as 1k when supply is < ~4V but currents limit above that.

• Use 0805 termination resistors maybe ? Or at least spec those as high power variants.