LCD or any other device not working unless power is connected to Arduino

Hi guys,

So basically I am just tinkering a bit around with Arduino and external devices, sensors etc.
I have a question, which can be for experts quite trivial, but I don’t quite understand why this is happening.

So currently I have LCD I2C connected to my Arduino with this code:

#include <LiquidCrystal_I2C.h>

//I2C pins declaration
LiquidCrystal_I2C lcd(0x27, 16, 2);

int i = 0;

void setup()
{
    lcd.init();
    lcd.backlight();
    lcd.setCursor(0, 0);
    lcd.print("Hello");
    lcd.setCursor(0, 1);
    lcd.print("World!");
    delay(3000);
    lcd.clear();
}

void loop()
{
    lcd.clear();
    lcd.print("COUNTER:");
    lcd.print(i);
    ++i;
    delay(1000);
}

So LCD is just displaying a counter over a loop.
Now, the LCD works as long it is connected to 5V and GND (besides SDA and SCL) pins.
But if I decide that I don’t want to “strain” Arduino with the power for LCD, I would like to connect the power pins of the LCD to some other 5V power source.
But as soon as I do that, it doesn’t work anymore.

So, would someone kindly tell me, why this is not working? I thought that for the communication between Arduino and LCD only SDA and SCL pins are necessary between them.

Also, if I would have many power consuming devices connected to the Arduino - let’s say many LCDs - how do I supply power to all of them? Surely I cannot connect all of them straight on to Arduino.

Any help is much appreciated!

Regards

Do you have a common ground between the arduino and the LCD?

Q: how should a Newbie know that a OneWire bus needs 2 wires, and a TwoWire bus 3 wires?

A: by reading General Guidance and How to use the Forum and COMMON GROUND

vinceherman:
Do you have a common ground between the arduino and the LCD?

The goal would be not to have a common ground or even same circuit.
The LCD as such is here just an example. It could be any device, or even something big with big power consumption. Something that cannot be powered over an Arduino.
The LCS is just an example for observation that I had.

Thanks

ZinggJM:
Q: how should a Newbie know that a OneWire bus needs 2 wires, and a TwoWire bus 3 wires?

A: by reading General Guidance and How to use the Forum and COMMON GROUND

The article about the common ground was exactly what I needed and it answered my question.

Thanks

fbele:
The goal would be not to have a common ground or even same circuit.

No!

Apparently you comprehend that now.