Re: Power and ground device using a digital pin

Projects General Guidance
1

I see no reason why that should not work. However you should be aware that if you connect the "ground" of the "chip" through a digital output set to "LOW" the voltage will not be zero, so you wont have a proper "ground" on the chip, and that may affect anything else you connect to it.
A proper schematic and link to the "chip" would be useful.

2

But then they'll stop working together with 3.3V logic.

3

Why not connecting vcc to the arduino pin and gnd just to gnd? To the board or arduino gnd pin

4

Connect GND to GND, Arduino output pin to VCC of the chip. Output high, the chip is powered, output low, the chip is shut down. There is no power advantage to switching both sides of the device.
I realize, you're trying to avoid 'splitting' your GND wire as well, but that's a bad idea. Wire it properly, GND is the reference for everything in the Arduino world.

5

By the way, there's a GND and +5V pin on the 6-pin header usually used for ICSP, if you need an extra of each.

6

@anon12124179
A digital output pin is not a power supply pin.
The output voltage is NOT regulated.
The voltage will fluctuate depending on the current draw and I’m sure your device doesn’t draw a constant current.
NOT a good idea.

The promini has 3 ground pins and two Vcc.

7

I needed something similar with a Pro Trinket for an I2C connection. A4 and A5 is I2C. I tied A2 to +5 and A3 to gnd with 26awg bus wire.

You can do the same and assure your digital pins are set as inputs, which they are by default.

8

Ok, I understandt that you want to plug your small board on top of the Arduino with the 4 pins aligned, like a small hut board.

Then as you suggest I would at least choose the GND pin of the Arduino and the next 3 pins: 2, 3 and 4. So, I think that you should connect both GND's.

I see two problems only. You shouldn't rely only on the pins for the mechanical subjection. Better additionally fix the board to something else, or make sure that it will have no tension. Specially if the pins will be only in one side of the board.

And as Jim said, the digital pins are not good as power source, although in this case it will probably work, but 18mV is significant. I have done it only with sensors that consume less than one mV.