Hello,
I have an ENS160 Adafruit sensor board in I2C connection and when I connect the Vin and GND to an external power supply, the ENS160 board doesn't output in the serial monitor. The Serial output returns when I place Vin to 5V of the Arduino board and GND to GND pin of the Arduino board.
Is there a way we can get the output from the board even when I connect the power pins to an external power supply?
Please use schematics, not words. Pen and paper is fine. Put out pin names, voltage, power source.
I'll take it an image example from: Overview | Adafruit ENS160 MOX Gas Sensor | Adafruit Learning System
but I'm using an Arduino Uno instead of the Adafruit Metro shown and I have also an 16x2 I2C LCD to read the output from the ENS160 board.
The power supply I'm using is the same as here: BBP-32701 Bud Industries | Development Boards, Kits, Programmers | DigiKey
Now after some tinkering, I managed to make it work but not sure if I'm correct from how I understood it.
My clue in understanding it is that ENS160 is communicating through I2C and I have read that it is required that I2C data lines, Vcc and ground (or maybe just ground) come from the same source and that it's the reason why I'm not getting data from the ENS160 board since I'm using an external breadboard power supply for powering the board by connecting the 5V and GND pins to the breadboard power supply and connecting the I2C data lines to the Arduino SDA and SCL pins.
Is this kinda correct?
I have managed to output the data to the LCD by loading the code first to the Arduino Uno board, unplugging the cable from my PC and plugging it to the USB A of the breadboard power supply
If it works it's likely correct.
Your post #1 tells about a Vin that's not found on the pictures. Is the red sensor cable the one You nean?
Yep, I've called it Vin, yeah.
Why does I2C should come from the same source as the ground pin
I2C uses 2 digital lines and every such signal connection needs a reference, GND.
Why is GND different for both boards when they're both 0V at least?
Why are you using a breadboard supply, while the same circuitry is built into the Uno.
Leo..
I wanted to have more 5V accessible for my other sensors
Hi, @roamingal
Gnd is just a reference for the circuit, gnd on the module and gnd on the controller have to be connected together so that they share the same reference level and current can flow and make the circuits.
That way signal from the controller and signal from the module have the same gnd reference to measure the signal voltage from.
Tom.. 
PS. I'm surprised it wasn't picked up from here;
The question was about the breadboard supply, not about the breadboard.
A breadboard supply has the same circuitry and limitations as the 5volt regulator on the Uno.
What other sensors, and what is your external supply (voltage).
Give us the whole picture.
Leo..
Thank you for the explanation. This is informative 
It's really just to have more 5V and 3V pins for my sensors. The breadboard power supply is connected to a 9V power source. I could of course set some digital pins to high but it's not working well with me.
For reference on what I am using, you can check out my previous post: UV, IR, UV/IR and other possible sensors for detecting fires
Just a project to detect fires over a distance so trying a bunch of sensors and see what works. Also do have an 16x2 LCD and relays connected to the supply besides the sensor that draws a bit of power which is also a reason why I'm using a breadboard power supply (direct to supply via female-to-female connectors, not really connected to a breadboard)
Note that the max current draw from a breadboard supply powered with 9volt on it's DC socket is about 250mA. More than that and the regulators (without heatsinks) will eventually go into thermal shut-down. This is the same for the DC socket of an Uno.
Leo..
Understood! So far after 12hrs of the device being on, it's still cool. Will of course try my best to keep it that way 
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