The Network PDU-S will be based on the Arduino Ethernet board, however instead of the ATMega328 I'm going to use an ATMega2560.
This is the same chip that is used in the Arduino Mega, and I've used
it in several designs before so I've already got most of what I need to
create the schematic.
For the Ethernet controller, I've chosen to use the same Wiznet W5100 chip as the Arduino Ethernet so I can take advantage of the existing code libraries.
I'm including a Max232 RS232 to TTL level converter in the design. This will be used for debugging, and possibly included in the final product to send/receive commands to RS232 compatible devices.
Here's the top level schematic designed in Kicad: