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I have a prototyping shield for an Arduino Uno. I accidentally plugged the shield into my arduino so that the pins were all "off by one". I didn't think this was possible, but it turns out that the extra pin just slips between the gaps in the pin headers:

enter image description here

I powered it on not realising. The arduino didn't show any LEDs, so I powered it down, saw my mistake, and plugged it all in again.

Now though A0-A5 are all reading high values (~900-1000 when I do analogRead(A0)), even when I have pulldown resistors on them, and they still read like that when I unplug my shield all together.

The digital writes all work perfectly.

I'm thinking that I've broken the Arduino. Is that possible, or could it be something else?

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There is not (yet) enough information to be certain, but it seems likely that you have damaged the Arduino.

If damage has occurred it's more likely to have been caused by what happened on the other side of the board, where pins carry power supply voltages. You do not say what your power source is or where it is connected (USB, 5V in, Vin, ...) but I'd guesstimate that the connection of UNO 5V to Shield 3V3 allowed back feed into the UNO by any of a number of possible paths. UNO Vin connects to shield ground and a second UNO ground connects to a second UNO ground - so if the UNO was powered via Vin you'd expect the power supply to have been shorted. This might damage some power supplies but usually not.

Can you please advise what voltage was connected and to what pin. And do shield pins all offset by 1 on the other side, as I've shown?

enter image description here

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  • Correct, all pins on both sides are offset by one. The power rail on the prototyping shield was connected to the 5V rail from the Arduino. I've also seen really strange behaviour where I have a boolean that keeps toggling between true and false even though nothing is writing to that variable (it did not do this before I plugged in the shield incorrectly), which makes me think that the something is seriously wrong. Pissed off that I broke my expensive ethernet Uno, but that's a learning curve I guess.
    – Mark Henderson
    Commented Feb 5, 2015 at 20:35
  • @MarkHenderson Look here and note address and seller ID. More below.
    – Russell McMahon
    Commented Feb 6, 2015 at 1:54
  • Whoah. Their plain Uno's are about 1/3 of the price of locally and their ethernet one is 1/4 of the price of one locally!
    – Mark Henderson
    Commented Feb 6, 2015 at 2:45
  • One rule in electronics (at least this is one I always practice) is to doble check all connections before plugging power in. I guess if you applied that rule, it would have save you money and time. In your situation particularly, that would have been easy and quick to spot. Should be a lesson learned for you!
    – jfpoilpret
    Commented Feb 6, 2015 at 6:14

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