Arduino UNO stopped responding

Hi,

I’m a newbie with the Arduino.
I got a new one just today and I played with it for a couple of hours (uploading example sketches and connecting a potentiometer and a LED) with no problems.
It’s an Arduino UNO and I used a MacBook Pro with Snow Leopard.

After a while I decided to test the Nokia5110 screen and I followed this tutorial to connect everything up: http://blog.3d-logic.com/2012/08/26/digital-clock-on-arduino-uno-with-nokia-lcd-display/
Before uploading the sketch from the same tutorial, I turned the arduino on, just to see if the screen would turn on.
Nothing happened, except for the power LED that went on as usual. I thought that I couldn’t see anything on screen probably because the sketch that was running at that time didn’t have anything to do with Nokia5110.
So, I loaded the sketch into the IDE and then I clicked Upload and I got an error saying that there was no device connected (or something similar).
I unplugged and plugged the Arduino again, but from that time on it stopped being recognized by my Mac.
I tried many things, I unplugged the Nokia screen and all the cables and jumpers, but nothing.
Then I tried with my iMac, but the Arduino is basically invisible to all my computers. I tried with another USB cable. Nothing.

When I plug it in, the power LED turns on and that’s it.
I tried the loop-back test described in this forum, but nothing.

I’m afraid I short-circuited it when I turned it on the first time while connected to the Nokia screen. I guess I broke it. I don’t see any other explanation.

What do you think guys?

Thx,
Marco

Looks like a problem with the communications controller. The tutorial you linked does not use digital pins 0 and 1 (RX/TX), and the screen runs on 3.3V, which shouldn't be a major problem even if it was accidentally connected (for a short while) to the wrong digital pin. So perhaps you have somehow erased the firmware but the circuitry has not been damaged.

Another possibility is that for some reason the board is permanently in reset mode. Check if there may be something keeping the RESET pin connected to GND (from above and from below).

By the way, can you just check from a terminal window, with the Arduino connected, that no device similar to /dev/tty.usbmodemABC exists?

Assuming that the hardware is not damaged you can reflash the firmware for the 16U2. It seems to be a pretty common procedure but I've never done it, so you may want to search the forum for instructions.

I ordered another Arduino and I will try to burn the firmware again with the new one... maybe I can still save it. Thx, anyway!