Arduino and Ramps powering up I want to run two stepper motors using Arduino Mega 2560 and RAMPS 1.4. But, somehow I burned the Arduino while I was connecting the motor and plugging the board to the computer. Can I plug external power supply and USB connection to the computer at the same time? ### Additional info from comments I am using RAMPS 1.4 with Polulo red stepper drivers and Arduino Mega R3. I am only using two Nema 17 stepper motors and not using any hotbed or anything else other than the two stepper motors for the x and y axes. I am feeding 11.9 V supply to the RAMPS board. When powered on, can I plug the USB to my computer? Suppose I have connected two motors on the X and Y outputs of the RAMPS, and the external power supply is on, then can I connect my Arduino to my PC using USB? Will it burn my board or not? My only trouble is that when the board is on load, connecting the USB to computer motors would take power by Arduino pins instead of the RAMPS external supply.

I had a similar issue building my Prusa i3 Mk2s clone. I was constantly hooking & unhooking my Arduino from my PC while the printer was plugged into the mains. At some point it had enough & it released some "magic smoke". Later on I found out this was the power regulator on the Arduino.

You shouldn't **need** to plug in the USB and the external power to the Arduino at the same time, but if you did, it is smart enough to only use one.

That being said, by default the RAMPS passes 12V straight to the Arduino in order to power it (the Vin pin).