Purchased my first UNO today and had a few joyful hours playing around with it creating all sorts of basic programs. The first time I connected up some led's to a few pins, I miswired the breadboard, and accidentally connected pin 11 via a led directly to ground without a resistor. I didn't see the led on pin 11 turn on, it wasn't working, and when I touched it it was quite warm. Pin 11 is now not behaving like the others, it seems to always send power no matter what instruction I give it.
Is it correct/reasonable to assume that I broke something, or is pin 11 special in some way? If I broke it, what did I probably break? the chip itself or one of the smaller/minature other things that are soldered onto the board? (Does one replace the chip, or the board?)
The output pins can safely carry about 20 mA current. What you did exceeded that, destroying the circuitry associated with the pin and possibly causing other damage to the chip.
It is possible to replace the ATmega chip, if you have an Uno with ATmega328 in the plug-in DIP package, and also possible to replace other types given the correct tools and skills. Otherwise, just buy another Uno (or Pro Mini clone).
Thanks jremington, yes the main chip is socketed. So I guess I was wondering if there is any way to know if replacing the chip is likely to help. I guess I am wondering what is the normal/typical failure mode when a led is connected without a resistor. Is it more normal to damage the chip, or more normal to damage the board, or is there no way to guess what might have been damaged?
(I expected I might accidentally break something along the way, but I did hope to not break something on day one )
It is unlikely you damaged the board itself. That particular pin on the processor only connects to two things, the header for pin 11 that you had the LED connected to, and pin 4 of the ICSP header, which I doubt you have ever used. The only possible way to damage the actual board would be to burn the wiring trace, but that is very unlikely if you are powering the UNO by the USB cable, since there is a fuse on the UNO and most USB ports would not supply sufficient current.
You can purchase the atmega328 chips pre-loaded with the bootloader for the UNO, get some extras in case of further mistakes (we all make more mistakes than we would like to admit).
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