After a comment on my article about what’s wrong with the Pi Zero suggested it’s to do with the lack of fixed network connectivity on the Zero, I bought a Waveshare Ethernet/USB Hub Hat for the Pi Zero and tested it with the M-Bus Master Hat. The tl;dr is that they interoperate just fine.

Some observations about the Waveshare Hat:

  • It’s not a “Hat” according to the Raspberry Pi Hat specifications primarily because it doesn’t include an EEPROM to allow the Pi to detect whether and what sort of a Hat is connected. This is actually a good thing for interop with other Hats, as the spec doesn’t support mulitple Hats (and therefore EEPROMs) simultaneously. This means with both Hats connected the Pi can detect the M-Bus Master Hat.

  • The Ethernet Hat only appears to use the GPIO connector for power, passing all GPIOs (and other pins) through. Therefore GPIO 26, which the M-Bus Master Hat uses to control M-Bus power, works fine, as do the serial pins which the M-Bus Master Hat uses to communicate with slave devices.

  • The Realtek RTL8152B 10/100M Ethernet driver IC is used by the Ethernet Hat. This is supported by the Raspbian kernel out of the box, meaning plug and play.

  • There is a schematic available for the Ethernet Hat (just as this is for the M-Bus Master Hat). This is handy to see how the Ethernet (and USB hub function) on the Waveshare Hat works, and for integrating into your own designs.

  • There is a small physical issue with running both Hats at the same time - the ethernet port on the Waveshare Hat ends up directly under an opto-isolator on the M-Bus Master Hat, meaning the M-Bus Hat doesn’t sit fully home on the Waveshare GPIO pin header, but works fine not seated fully home. I’d recommend using a 12mm spacer between the Hats.

  • As the Ethernet Hat uses USB rather than GPIOs to provide the ethernet connectivity it comes with a funky double micro-USB male board, which connects the second micro-USB port from the Pi Zero to the Ethernet Hat. This works well as a solution, and provides additional rigidity to the Ethernet Hat even if not using spacers. 2 spacers do come with the Hat, which is a bit stingy when they cost at most a few pennies. I assume they are intended to be used on the side of the board without the GPIO connector.

All in all this Hat seems like a decent solution for providing fixed ethernet connectivity to a Zero and connecting other Hats at the same time.

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