I'm doing a relatively simple project using an Arduino Uno. A 13.8V benchtop power supply is powering my stepper motor/driver, and my arduino has been being powered over USB as I program it and test. My arduino uno is mounted right next to my usb driver, which is mounted next to a solderless breadboard. My 13.8V supply and the arduino are grounded together (the grounds are connected at the stepper motor driver GND terminal).
With my code working I spend approximately .8 seconds jumping Vin to a 13.8 rail on a breadboard right next to it and unplug the USB. And now, my code won't work. The lights are on (the green power led) but nobody is home. If I unplug Vin, and plug it back into USB, I'm back in business and it functions.
I'm stumped. 13.8V is slightly over the recommended 6-12V but it's 20V tolerant, and any fully charged 12V battery is going to be 13.8V or more. I've triple checked the gnd connection. Does anyone have any idea why my code won't run?