Hi this is my first post!
I have an Arduino MEGA-ADK. I build a simple testing scheme to light up a LED with a sensor. And when it is plugged into the PC’s USB works perfectly. But when I turn on a external power 12VDC, 1A, positive internal source, nothing happens. Nothing at all. No light or LED on the Arduino board works.
Does the external input is damaged? How could I check?