Do you actually know why the pull-down resistor solved the problem though?
Hero, Yes. It is because other wise the pin is 'floating', so with the pull-down resistor, it is tied to ground, but when you flip the switch and make it high, the 10k prevents a large current flowing through the short.
If there is something other than this that I have missed, please share, as I am very eager to learn, and not just plug in stuff. In other words, I'd rather know why I need a pull down resistor, and why I need it, than just know I have to have one.
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The Atmel uC should have internal pull-ups, shouldn't it? Aren't they implemented in the Arduino processing code?
I am not sure. This sounds slightly familiar. Something tells me that you have to enable it in the code, though. (That could be wrong)
Joshua