2

I want to make a sketch which behaves differently, i.e.:

pinMode(pin1, OUTPUT);
digitalWrite(pin1, HIGH);

pinMode(pin2, OUTPUT);
digitalWrite(pin2, LOW);

pinMode(pin3, INPUT);
// And a user decides to short pin3 with pin1 or pin2

if (digitalRead(pin3) == HIGH) {
  // behavior 1
} else {
  // behavior 2
}

But, I wonder whether shorting two pins with/without a resistor safe or not. If it is dangerous, what is an alternative way to do such a thing?

Jeon
  • 123
  • 1
  • 7
  • You are connecting 5V to ground, with a near zero Ohms wire. Calculate the current. –  Aug 10 '17 at 09:45
  • I would pinMode(pin3, INPUT_PULLUP);, this way you condition the sketch on the pin being either grounded or not. You can then connect a switch between pin 3 and GND to have the switch control the behavior. – Edgar Bonet Aug 10 '17 at 14:55

1 Answers1

3

Firstly, why would you?

All you are doing is connecting the input pin 3 to either VCC or GND, since that is what setting a GPIO to HIGH or LOW gives you - why would you waste two GPIO pins for that purpose?

"shorting" an input pin with VCC or GND is what you do with a button or switch anyway. The resistor in that case is used to hold the pin in the opposite direction when the button isn't being pressed. The same effect can be created using a two-way switch connecting the pin to either VCC or GND with no resistor required.

So yes, you can "short" the input pin with an output pin safely - as long as that input pin never becomes an output pin at any time (hint: never use pin 13 on an Uno for this - it becomes an output to flash the LED during the bootloader over which you have no control. The same goes for the TX pin.)

Majenko
  • 105,095
  • 5
  • 79
  • 137