Hello, I am having a problem powering an Arduino and Ethernet shield together using the Arduino's barrel connector. The duo runs fine, and the sketch executes as intended, when powering them from the USB connector. I even had it running by way of an iPhone 5v wall charger as the source into the USB jack with success.
When connected via the barrel jack, using anything from a stable 5v benchtop PSU to a 12v power brick, only the red power LED on the ethernet shield glows dimly if I use my Duemilanove board as the host. And, the onboard pin 13 LED of the shield glows, along with the power light, if I use an Uno board on the bottom. I do not see any of the ethernet activity lights using either Arduino board and the barrel plug.
I have also uploaded the blink sketch to both Ardunio boards by themselves (without shield attached) and was successful in powering each of them using the barrel connector from all source voltage supplies mentioned. So, both Arduino boards, and their onboard regulators, seem to function just fine.
The last test I performed was running the blink sketch while having the ethernet shield connected. With this configuration, again using the USB connector, both onboard LEDs blink, power lights appear bright and (most important) the ethernet activity lights are, well, active. However, trying to power even this configuration using the barrel connector still fails as mentioned above. (EDIT: the shield's onboard pin 13 LED does in fact blink when running blink sketch along with using the barrel plug, just no ethernet lights work)
Am I to assume the ethernet board is causing this failure of the power circuit? Is there some configuration (jumper, etc) that I'm missing while having both boards connected together? Any suggestions on cause and possible workarounds are greatly appreciated.