Couldn't find USB port, power surged through - what happened?

Development Tools IDE 1.x
1

So i was messing around with a 6V and 1.2 Amp unipolar stepper motor, using only the 5 V power source from the arduino UNO.
I was trying to use different codes, but suddenly when i tried to upload, the arduino software couldn't locate the serial port, even though it was connected, and i could see the USB powered the arduino board.

Just to test the board i hooked it up to another setup where i had a couple of LED's drawing power from 5V (among other things) the LED's were constantly on which were definitely not the intention.

Then i tried to do the simple blink sketch and it still couldn't locate the serial port, so the code would not be uploaded and thus nothing happened.

I switched to another arduino UNO, now the software could locate the Serial port, and it ran perfectly.

I tried using the reset button, which didn't work either, so i thought i had fried something on the board.
Feeling desperate i tried using reset again a couple of minutes later and then, the one i originally thought i had ruined worked like nothing had happened to it.!

So can anybody explain what had happened, so i can find the error in my ways?

Thank you very much.

stepper-motor1-400x397.png

2

Hello!

I am new at Arduino forum, but I guess you fried something on the way from voltage regulator to micro controller .
Arduino uses voltage regulator AMS1117 (http://www.advanced-monolithic.com/pdf/ds1117.pdf) with output 1A which might be still enough to power, although high power current should damaged ATmega. Try exchange it with the working one form your second Arduino.

3

Arduino has a resettable fuse between USB power and the board. Its possible you got that hot enough to trip, and when it cooled it allowed USB power to flow again.

4

What causes this heating, and is there a way to avoid it?
External power source for the stepper?

5

External would be much better. Preferred, actually.