I2C is open collector. It won't work without pullup resistors. If it's working for you it must be because you are using some modules that have the pullups built onto the board. Turn off the power and measure the resistance from SDA to 5V and SCL to 5V. Post the values.
I don't remember putting a pullup resistor, i made homemade PCB's and they worked preaty good without
pullup resistors, no joking.
A meter should be fine.
Yea but I'm not sure yet i will need only a meter or more so I want to find a way to be safe with my
project not to redo everything :D
google i2c extender if you need more length or it does not work.
I didn't knew that kind of things exist :D it's like power line amplifiers, nice I know how they work
theoretically but need to give a better look on them so see exactly how they work.
Maybe a silly question, but why don't you use RS485 for communication between Arduinos (sensors is a different story)? It was designed for long distances.
Never worked with it so I don't know many things about it.
Looking at it right now I understand why people use it, double shield, nice way / protection from noise
and enough cables to work with, I will keep it in mind about this cable.
Not according to the master/slave tutorial; no pullups for unknown reason but it does work ;) I did not look at the library; it might enable the internal pullups for the slave?
I build my own PCB's 3x atmegas connected together without pullup resistors for some reason it worked
probably internal pullups not sure, but I will keep in mind to put pullups next time.
Btw a question:
How exactly I determin the value of the resistors by the length of the wire?
Giving a 2nd look to I2C extender will be nice to use it because in that way i can make my modules
portable and plug and play any time.