Grounding if i2c device has its own power supply

[ECE9]

I have a device which has i2c connection and this device has own 5v power supply. If I try to control that device with Arduino Uno, do I connect SCL to SCL, SDA to SDA and GND to GND? Do I need any resistor to GND connection?

[Idahowalker]

Connect the gnd's together. Why would you need a resistor on ground/circuit neutral?

[DrDiettrich]

@Idahowalker

ground/circuit neutral?

Only logic GNDs should be connected. This includes all Vcc supplies. Protective grounds or mains Neutral should not normally be connected to electronic devices.

[Idahowalker]

Of course.

[PerryBebbington]

@ECE9
You might find this useful:

Common ground and why you need one

A common mistake for people new to electronics is to have 2 circuits fed from different power supplies with signals passing between the circuits, but with the grounds not connected. This leads to questions asking why the project doesn't work. You don't have to spend long reading the questions on this forum to see this is asked often. Here I attempt to explain the problem and why it matters to connect the grounds. Note that in all of the schematics that follow I have used a battery as a power sup…

[JohnRob]

The grounds must be common else there is no reference for what voltage is high or low.

I usually start with a 100 ohm or so resistor between grounds until I prove there is no other path that would cause a high current to flow between. This is just a precaution I use. Once everything is working you can eliminate this resistor.