Use anolog ports to Power an I2C RGB LCD display, current not sufficient

Hi there,

I'm connecting a Grove-LCD RGB Backlight display.

SCL on A5
SDA on A4
VCC on 5V
GND on GND

No problems, nice crispy display.

Just like with a Nunchuk I tried to use A3 as 5V and A2 as GND. I added the following lines to my sketch.

pinMode(A3, OUTPUT);
digitalWrite(A3, HIGH);
pinMode(A2, OUTPUT);
digitalWrite(A2, LOW);

The display works but not very much contrast.

Is there some kind of current limitation on the analog ports. I measured the current in both setups. 19mA in the first setup and 15mA in the last.

Is it possible to use A3 en A2 as Vcc and Gnd for this display. It is so much easier to connect (I build a Grove to 4 pin mail header).

Greetings

Erik Verberne

Is it possible to use A3 en A2 as Vcc and Gnd for this display. It is so much easier to connect (I build a Grove to 4 pin mail header).

What do YOUR observations tell you?

Look up how much current the 5V pin can source.
Look up how much current the A3 pin can source (a LOT less).
Look up how much current the LCD consumes.

This display : http://www.seeedstudio.com/wiki/Grove_-_LCD_RGB_Backlight ?

Operating Current<60mA

The 19mA and 15mA you measured can be supplied by a pin. However, if you use a pin for 5V and a pin for GND, then the voltage will drop twice as much. Using two ( or 8 ) pins for 5V and two ( or 8 ) pins for GND is better.
Doing such things is so ugly ! And if you do it wrong, there can be a shortcut between the pins. Or you can damage the display with a negative voltage at the I2C pins.
A design with a floating GND (created by pins) is bad, it can cause a lot of trouble later on.

Therefor, please don’t do such things. Get a normal GND and normal 5V. I’m gonna say: “told you so” in advance, in case you run into trouble later on :wink:

Could you modify the subject of your top post ? This is not an I2C question, but a question about using analog pins to power a display.

Thanks for your input. Understood, not a good idea to abuse the anolog ports. Too bad.

Discussion closed.