Arduino Tutorial

By LiterallyTheOne

6: Interrupt

Introduction

• Previous tutorial: Analog
• This tutorial: Interrupt

External Interrupt

• Special Signal
• Pause the current action
• Run a code in a function
• Interrupt Service Routine Function (ISR Function)

External Interrupt in Arduino Uno

• 2 External Interrupts
• pin 2, 3

Setup LEDs

Write a Routine

#include <Arduino.h>

int led_pins[8] = {6, 7, 8, 9, 10, 11, 12, 13};

int current_led = 0;

void setup()
{
  for (int i = 0; i < 8; i++)
  {
    pinMode(led_pins[i], OUTPUT);
  }
}

void loop()
{
  digitalWrite(led_pins[current_led], HIGH);
  delay(200);
  digitalWrite(led_pins[current_led], LOW);

  current_led++;
  current_led %= 8;
}

Output of LED setup

Connect an Interrupt

• Button is Normally Closed
• Default: 5V
• Change: 0V

Define Interrupt in Arduino

• attachInterrupt
  • pin
  • ISR function
  • mode

Define Interrupt pin

• digitalPinToInterrupt

attachInterrupt(digitalPinToInterrupt(2), ... ,...);

Define ISR function

void isr_pause()
{
}

attachInterrupt(digitalPinToInterrupt(2), isr_pause ,...);

Modes

Mode	Description	figure
LOW	trigger the interrupt whenever the pin is low.
CHANGE	trigger the interrupt whenever the pin changes value.
RISING	trigger when the pin goes from low to high.
FALLING	trigger when the pin goes from high to low.

Add mode

attachInterrupt(digitalPinToInterrupt(2), isr_pause, RISING);

Fill the isr function

#include <Arduino.h>

int led_pins[8] = {6, 7, 8, 9, 10, 11, 12, 13};

int current_led = 0;
int x = 1;

void isr_pause()
{
  x = 1 - x;
}

void setup()
{
  for (int i = 0; i < 8; i++)
  {
    pinMode(led_pins[i], OUTPUT);
  }

  attachInterrupt(digitalPinToInterrupt(2), isr_pause, RISING);
}

void loop()
{
  digitalWrite(led_pins[current_led], HIGH);
  delay(200);
  digitalWrite(led_pins[current_led], LOW);

  current_led += x;
  current_led %= 8;
}

Output of pause interrupt

Volatile in Cpp

• Stops Compiler optimazation for a variable

volatile int v;

Reset with Interrupt

Increment pattern

LEDS dance

Link to the tutorial and materials