I have an Arduino Mega and a Arduino Ethernet shield. I would like to add a SmartTthings shield on top to have it communicate with the ST Hub via ethernet . Does anyone know if this is possible? Can I just plugin the ST shield on top of the Arduino ethernet shield? If not how else can I get my Arduino Mega to communicate with the ST Hub via ethernet.
I think you are a bit confused with the purpose of Arduino SmartThings Shield.
Shield is a Zigbee module on top of Arduino that connects to the ST Hub directly vie Zigbee protocol.
If you already have a Shield, you don’t need a Ethernet shield and you can pair it to ST hub using instructions from here: http://docs.smartthings.com/en/latest/arduino/index.html