Digital pin to interrupt question

Projects Programming
1

Hi,

More issues.

This program doesn't work at all, but I am mystified why digitalPinToInterrupt returned a negative value.

The program returns 26, -1. Is that right?

#define I_PIN_KEY_PRESSED 26

volatile boolean KeyPressed = false;

static void KeyPressedISR(void) {
   KeyPressed = true;
   digitalWrite(LED_BUILTIN, HIGH);
}


void setup() {
   pinMode(I_PIN_KEY_PRESSED, INPUT);
   pinMode(LED_BUILTIN,       OUTPUT);
   
   attachInterrupt(digitalPinToInterrupt(I_PIN_KEY_PRESSED), KeyPressedISR, RISING);

   Serial.begin(9600);

   Serial.println();
   Serial.print(I_PIN_KEY_PRESSED);
   Serial.print(", ");
   Serial.print(digitalPinToInterrupt(I_PIN_KEY_PRESSED));
}

void loop() {
   //Serial.println("");
   //Serial.print(KeyPressed);
   //KeyPressed = false;
   
   delay(2000);
}
2

Which board?

3

Did you mean

   Serial.print("I_PIN_KEY_PRESSED");
   Serial.print(", ");
   Serial.print(digitalRead(I_PIN_KEY_PRESSED));`
4

No, the OP literally asks why

 digitalPinToInterrupt(I_PIN_KEY_PRESSED)

is -1.

Which is what prompted @anon73444976 to ask for what board.

26 is not a valid pin in this case, it seems, and a retrun value of -1 is the way you find that out sometimes.

a7

5

There is rarely a need to use an interrupt for a key press if your code is written properly. See the following tutorial:

StateChangeDetection

6

Good question. Indeed depending on the board, only some specific pins can be used for interruptions.

7

The board I'm using is a Arduino Mega.

8

Essential reading.

9

What are you trying to achieve with your program?

10

May be an X-Y problem, which is why I asked

11

I really caused this problem myself, so I'm putting my hand up.

I was testing the hardware using a Mega intending to shift everything to a Due and made the simple but wrong assumption the two were the same, not so.

All of the digital pins on a Due can be configured to interrupt. Not so on a Mega where there are only 6 interrupt pins and are dedicated to a specific pin.

I've learnt something: Some things are not the same!

Tested the board using pin 26 as an interrupt and it works as expected.

Now to move on and get the address switches and LED output's going.

Thanks for the help.

12

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