I am experiencing a weird issue where my pin 13 on my arduino uno starts blinking rapidly and then pauses and continues this indefinetly when I plug in the board. It continues blinking until i enter anything into either the serial monitor or on putty connected to the serial port.
Once i do that, the programming I have uploaded starts up. Pushing reset only stops the blinking for as long as I hold reset down.
It doesnt matter what I have uploaded either, uploaded the blink example and still had the same issue.
I have a cellular shield, and a protoshield v2 stacked on top. and the uno board by itself is fine. when I plug it in, the blink program runs successfully from the getgo.
The problem occurs when I add on the cellular shield, even without the protoshield on top of it. Connected to power using the barrel jack, everything works fine. but when unplugging from the usb, and plugging it back in again, it fails to load correctly.