Introduction :
An
interruption, as its name indicates, interrupts momentarily the program
executed by Arduino to perform another task. When the task finishes, the
program takes on the lead from the axact place where it was interrupted.
Interruptions
could be ideally used for listening to user’s actions, for example pressing a
button, a keypad, or the changing state of a sensor without the need of
constantly reading a pin’s state.
How does it work ?
Arduino
Uno (ATMega328) can manage 2 external interruptions on its pins INT0 and INT1
mapped to pins D2 and D3 on the microcontroller board.
Interruptions
could be triggered under 4 modes :
- LOW : The pin is in a low state
- RISING : The pin passes from low to high state
- FALLING : The pin passes from high to low state
- CHANGE : The pin has changed state
Creating an interrupt :
To
“listen” for an interruption on Arduino, you only have to attach an interrupt
on either pin D2 or D3 using the method attachInterrupt. This method takes as
an argument the interruption’s pin number 0 or 1, the name of the function
called by the interruption, and finally the interruption mode as the following
example shows :
attachInterrupt(0, myInterrupt(), RISING);
Even though Arduino’s pin is D2, we indicate 0 for the interruption’s pin (0 for INT0 / D2, 1 for INT1 / D3).
The
function attached to the interrupt have to take a small amout of time to
execute and it is also forbidden to use time based instructions in the interior
of the function as it blocks the microcontroller.
Application :
In
the following application, we attach an interruption to a push button. The
program writes the interruption number to the serial monitor every time the
button is pushed.
Code :
int interruption = 0; //interrupt 0 is on digital pin 2
volatile int numInterrupt = 0; //variables used inside interrupt functions declared as volatile
void setup() {
Serial.begin(9600);
attachInterrupt(interruption, functionInterruption, FALLING);
}
Void loop() {
//simulating a task being executed repeatedly
While(true) {
Serial.print(“.”);
delay(250);
}
}
Void functionInterruption() {
Serial.print(“Interrupt numero ”);
Serial.println(numInterrupt);
numInterrupt++;
}
volatile int numInterrupt = 0; //variables used inside interrupt functions declared as volatile
void setup() {
Serial.begin(9600);
attachInterrupt(interruption, functionInterruption, FALLING);
}
Void loop() {
//simulating a task being executed repeatedly
While(true) {
Serial.print(“.”);
delay(250);
}
}
Void functionInterruption() {
Serial.print(“Interrupt numero ”);
Serial.println(numInterrupt);
numInterrupt++;
}
