I2C protocol - Common power supply mandatory?

[awneil]

@anon70927101

Why the power supply must be common?

You don't need a common power supply, but you certainly do need to have a common GND.

The GND is what provides the reference point for each board to determine whether signals are at zero or one (or any other level) - without a common reference, that won't work.

But the power supplies can be different - just beware of leakage if one is turned off while another is still on ...

Addenda

GND separation and separate power supply

The sensors and the Arduino need a common GND to give a common point of reference for the measurement of the voltage level by the Arduino The sensors and the Arduino should have a common GND connection, then you can sense the voltages on 3 separate Arduino pins What type of sensors are they

Same Ground when running multiple Power Sources

If you supply 12-24V to the sensors and 5V to the Arduino and use a common GND then, as long as the sensors really do only output a 5V signal then you will be OK Without a common GND connection the Arduino has no reference against which to measure the voltage of the sensor output You can say that again. What application are you using them for ?

Sometimes you might appear to get away without a specific GND link - but it needs to be provided somehow; eg,

Serial communication between ESP32 and Arduino UNO

Sorry, I did not see a link Powering both devices from the PC is not a problem but have they got a common GND connection ? This is often not needed due to the common USB GND but I would add one anyway