Two simple questions

Hi,

First… do I have to use 4,7k resistors connected to +5 and SDA, SCL when I am using I2C?
Second… I want to use a diode which protect that + is conected to + and - to -, but I am not sure if I do it correct.
Like this?

GND — -power jack+ — ->|- — +5

->|- this is my diode

do I have to use 4,7k resistors connected to +5 and SDA, SCL when I am using I2C?

In general, no. The ATmega has internal pullups that the Wire library enables.

If you have lots of devices and/or long runs on the bus, stronger external pullups may be necessary.

-j