I/O PIN Protect

Using Arduino General Electronics
1

I'm using a coin selector to detected when a coin is inserted,

it's 12v connected and they have a signal cable, i put it on the pin 6 but right now is dead, what can I do to protect the I/O ?

2

You can use a high-value resistor (like 2.2k) to limit the current.

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The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected

3

You already got a pretty good answer at Pin dead/burned - #11 by CrossRoads - Programming Questions - Arduino Forum

A more extensive protection would be to use a zener diode and resistor, or even go for an opto isolator.

4

Better still use the signal to drive a transistor. Connect the emitter to ground, the collector to input and the base through a large resistor to the signal. And enable the internal pull ups.