With RainMachine version new .920 using USB to ethernet adapters on HD12/16 family works but it's *officially unsupported*.
Most of the USB 2.0 adapters should work, especially those who market compatibility with Windows XP without installing any drivers. For a short list see the end of this post.
To use ethernet just plug the usb to ethernet adapter in the spare USB port *without* physically removing the WIFI adapter. You can use the Settings >System > WIFI to disable the WIFI from the software. After reboot the ethernet should be working with DHCP.
1. The ethernet only works with DHCP there is no easy way to configure static IP.
2. WIFI stick needs to be left inserted in the USB port.
3. On device Network Tools output doesn't work for ethernet
4. Can't start updates from device. Updates can be started from mobile/web applications
5. On certain cases the device might not appear on local discovery from mobile apps. To workaround, you can use Direct Access from Network Settings (from mobile apps Devices screen) to specify <device IP:8080>.
Adapters listed as compatible (some adapters might have newer versions that might not work):
Intellinet, ST Lab USB Ethernet
Hawking UF200, TrendNet TU2-ET100
Billionton Systems, USB2AR
Buffalo LUA-U2-GT 10/100/1000
Sitecom LN-029 "USB 2.0 10/100 Ethernet adapter"
corega FEther USB2-TX
goodway corp usb gwusb2e
JVC MP-PRX1 Port Replicator
ASIX AX88772B 10/100
ASIX AX88772 10/100
ASIX AX88178 10/100/1000
Linksys USB200M Rev 2
0Q0 cable ethernet
DLink DUB-E100 H/W Ver B1
DLink DUB-E100 H/W Ver B1 Alternate
Apple USB Ethernet Adapter
Cables-to-Go USB Ethernet Adapter
ABOCOM for pci
Asus USB Ethernet Adapter
TechRise Ethernet Adapter, USB 2.0 to RJ45 Fast Ethernet LAN Network Adapter
Please follow the discussion on our forum: https://support.rainmachine.com/hc/en-us/community/posts/115005924527-Ethernet