Here is my problem: I have an arduino duemillanove board + an arduino ethernet shield. If I'm using a 9V battery to power on everything is ok. The ethernet board is attached to a router and i can run the Hello Word example in a web browser.
I'm made a simple shield to control a DC motor using L298N (H Bridge) when attaching this shield to arduino board everything works ok. The Arduino board is powered from a 9v battery and the IC l298N from 4x1.5v and it's ok.
Now came the problem if am stacking both shields(ethernet+motor) when all are connected to computer using usb cable everything is ok, i can control the motor using the web interface. If I'm using the 9v external power for Arduino board is not working (from router i see there is no activity on the ethernet plug). I've increase the input power using an external AC-DC adaptor of 12v 1000mA, still not working.
Any clues why this happening?