Will connecting an output pin to 5.1V and bringing it low break the board

I'm using an Arduino Nano, and i was wondering if i could connect a 5V pin to an output pin and pulse it low (I need to do it to move a stepper motor). After measuring the current it looks like it doesn't exceed the maximum amount of current the output pins can take (0.2mA), but i'd still like to be fully certain so that i don't damage the board.
I'm sorry if this question has been asked before, but my googling skills are terrible and i couldn't quite find what i was looking for.

What is a “5 volt pin”?

If you just mean another I/O pin that is configured as an output, you are fine.

Or an I/O pin from another chip, board, module or whatever.

Otherwise, “depends”.

If you’ve measured the current and haven’t broken anything, that’s probably what you are doing and you are probably OK.

So what are you doing? :wink:

a7

Sorry that doesn't make very much sense. What else is connected to these pins you're talking about? In general connecting a digital pin directly to the 5V output pin and then trying to set it low i.e. 0V will almost certainly damage something. But why would you want to do that? Can you provide a schematic showing exactly what you have connected where? A photo of a pencil drawing would be fine.

Steve

alto777:
What is a “5 volt pin”?

If you just mean another I/O pin that is configured as an output, you are fine.

Or an I/O pin from another chip, board, module or whatever.

Otherwise, “depends”.

If you’ve measured the current and haven’t broken anything, that’s probably what you are doing and you are probably OK.

So what are you doing? :wink:

a7

I'm trying to move a motor on a floppy disk drive. To do so, I need to pulse a data pin to ground, and i'm trying to do that with an Arduino. I've measured the current by just connecting it to the ground of the floppy disk drive. I've also just realised that i measured the current wrong, and it's actually 10mA, but that still seems to be on the safe side of things.

The normal way to do what I think you're saying is to connect a pull-up resistor between 5V and the output pin. Otherwise you are shorting the 5V supply to ground.

Steve

That's what im trying to do, the step pin needs to be grounded to move.

You can "freely" write high (~5V) or low (~0V or "ground") to an I/O pin as long as you don't exceed the "absolute maximum" current of 40 mA in either direction. When the output is low and current flows in*, we say the pin is "sinking" current. When the output is high and current flows out*, we say the pin is "sourcing" current.

So you can write a high or low and leave it all day or briefly pulse it to the opposite state, etc.

If you "short" an output pin to 5V power or ground you'll get excess current when you try to write the opposite state and you can potentially fry the Arduino. The same thing can happen if you short two output pins together. (It's OK to short/connect multiple input pins together or to connect an input pin to 5V or ground.)

When you measure current with a multimeter, make sure to hold the state for at least a couple of seconds to get an accurate reading. And, I assume you know how to measure current? ...You have to "break" the circuit and insert the meter in series.

the maximum amount of current the output pins can take (0.2mA)

The recommended maximum is 20mA (0.02A) per pin. The datasheet for the chip rates the absolute maximum at 40mA (0.04A) per pin and 200mA total (when multiple I/O pins are sourcing or sinking current).

  • "Conventional current flow" is positive-to-negative.

Some tutorials and videos tell noobs to use a small (150 ohm) resistor in series with whatever an output is meant to drive.

This limits the current in case of accident and for the most part will allow the original unprotected circuitry to function normally.

Not a noob, I don't do that. I haven't tried it but it seems plausible. I've also forgotten ever damaging an output and have been from time to time pleasantly surprised when something I managed to hook up did not. The chips seem fairly robust.

a7

Thank you for your help, this seems to be the answer i was looking for.

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