Shorting I/O pins to Ground

Projects General Guidance
1

Hello all,

I have been reading this informative page from ruggedcircuits.com 10 Ways to Destroy an Arduino — Rugged CircuitsRugged Industrial Arduino Microcontrollers) where it is said that shorting a pin to ground will destroy the pin.

However, a while ago I was advised to attach a sensor in such a way that when it is activated it shorts the pin (a technique that I am currently using without issues) to bring it low, in this thread Could someone take a look? - #7 by system - Sensors - Arduino Forum.

I am confused as to why the pin is not destroyed when the sensor connects it to ground.

Can someone enlighten me?

TIA

2

I am confused as to why the pin is not destroyed when the sensor connects it to ground.

Can someone enlighten me?

It all depends on what the pin is configured to be, an input pin or a output pin. At power up and reset time all pins default to be input pins. Input pins are very high input resistance (high impedenace) so they draw almost zero current for any voltage applied to them between 5vdc and ground. However once you command a pin to be an output pin then it is at all times either an active LOW (0vdc) or active HIGH (+5vdc) level and when connected to external components will sink or source current through the pin. Output pins have a maximum safe current rating and if exceeded, will destroy the pin and possible the chip.

That help?

Lefty

3

To answer your question specific to the post you referenced, that sensor's C -> E has a high intrinsic resistance; it prevents excess current from running through it so an external resistor is not needed.

4

retrolefty:
It all depends on what the pin is configured to be, an input pin or a output pin....

Ah, I see. That makes sense.

...that sensor's C -> E has a high intrinsic resistance...

That makes sense too.

Thank you, Lefty and Chagrin! :slight_smile: