MEGA1280: Using power supply vs USB - Sketch Start

So riddle me this:

Why does everything start up fine when I power from USB, however, if I plug 5v (or 6v) power supply nothing happens (program doesn't seem to start)?

Danny

Looks like a 9 volt DC supply works! Wonder why a 5v or 6v doesn't.

Danny

Looks like a 9 volt DC supply works! Wonder why a 5v or 6v doesn't.

The input voltage goes through a voltage regulator. The voltage regulator needs greater than 5V in to generate a 5V out. Typically, 7.2V+ in is required to get 5V out.