I2C resistors

[MikiMouse]

i am newbie at electronic. I would like know why I need to have resistors on I2C (SDA, SCL). In some schematics are the resistors, in another are not.

[David]

some devices connected to I2C bus have internal pull-up resistors, other have no resistors. You need to check datasheet for each device component connected to I2C. Then you need to calculate all resistor including external pull-up resistors to get a total current max. 3 mA. Check this document:
https://www.joshmcguigan.com/blog/inter ... istor-i2c/