Tutorial Understanding Blink Without Delay | How to millis

In this tutorial, we will learn how BlinkWithoutDelay example can be use to do multiple task at the same time.

Circuit Diagram:

Video Demonstration:

Source Code:

1. Blinking 3 LED in Different Intervals:

// LED definitions for easy reference
#define RED_LED   A0
#define YEL_LED   A1
#define BLU_LED   A2

// variables for the red LED
bool ledState_RED = LOW;            // this holds the current state of the red LED
unsigned long prevMillis_RED = 0;   // this holds the start time of millis for computing the elapse time
unsigned long interval_RED = 3000;  // this holds the interval of each toggle of LED

// variables for the yellow LED
bool ledState_YEL = LOW;            // this holds the current state of the LED
unsigned long prevMillis_YEL = 0;   // this holds the start time of millis for computing the elapse time
unsigned long interval_YEL = 5000;  // this holds the interval of each toggle of LED

// variables for the blue led
bool ledState_BLU = LOW;            // this holds the current state of the LED
unsigned long prevMillis_BLU = 0;   // this holds the start time of millis for computing the elapse time
unsigned long interval_BLU = 7000;  // this holds the interval of each toggle of LED

unsigned long currMillis_ALL = 0;   // this holds the current time captured by the millis() function
                                    // it is use in general for synchronization purpose

void setup() {
  // Set the pin directions for LEDs
  pinMode(RED_LED, OUTPUT);
  pinMode(YEL_LED, OUTPUT);
  pinMode(BLU_LED, OUTPUT);
}

void loop() {

  // Store the currently time
  // Notice: it use a single current time for synchonization with other function
  currMillis_ALL = millis();

  // Virtually process all the task
  process_RED();
  process_YEL();
  process_BLU();

}

void process_RED() {
  if (currMillis_ALL - prevMillis_RED >= interval_RED) {
    // Elapse time has reached the interval
    // Save the current time as previous time
    prevMillis_RED = currMillis_ALL;

    // toggle LED state
    ledState_RED = !ledState_RED;
    
    digitalWrite(RED_LED, ledState_RED);
  }
}

void process_YEL() {
  if (currMillis_ALL - prevMillis_YEL >= interval_YEL) {
    // Elapse time has reached the interval
    // Save the current time as previous time
    prevMillis_YEL = currMillis_ALL;

    // toggle LED state
    ledState_YEL = !ledState_YEL;
    
    digitalWrite(YEL_LED, ledState_YEL);
  }
}

void process_BLU() {
  if (currMillis_ALL - prevMillis_BLU >= interval_BLU) {
    // Elapse time has reached the interval
    // Save the current time as previous time
    prevMillis_BLU = currMillis_ALL;

    // toggle LED state
    ledState_BLU = !ledState_BLU;
    
    digitalWrite(BLU_LED, ledState_BLU);
  }
}

2. Demonstration for delay blocking code:

#include "LiquidCrystal.h"

#define SW1 7
#define SW2 6

LiquidCrystal lcd(A0, A1, A2, A3, A4, A5);

void setup() {
  // put your setup code here, to run once:
  lcd.begin(16,2);

  pinMode(SW1, INPUT_PULLUP);
  pinMode(SW2, INPUT_PULLUP);

  lcd.setCursor(0,0);
  lcd.print("SW1 to delay    ");
  lcd.setCursor(0,1);
  lcd.print("You can press S2");
  
}

void loop() {
  
  if (digitalRead(SW1) == LOW) {
    lcd.setCursor(0,0);
    lcd.println("SW1 is pressed  ");
    lcd.setCursor(0,1);
    lcd.println("Uno delay: 5 sec");

    delay(5000);
    
  }

  if (digitalRead(SW2) == LOW) {
    lcd.setCursor(0,1);
    lcd.print("S2 is press     ");
  } else {
    lcd.setCursor(0,0);
    lcd.print("SW1 to delay    ");
    lcd.setCursor(0,1);
    lcd.print("You can press S2");
  }
  
}

3. Or you might want to blink the 3 LEDs in different intervals and also controls the duration of ON and OFF

// LED definitions for easy reference
#define RED_LED   A0
#define YEL_LED   A1
#define BLU_LED   A2

bool ledState_RED = LOW;
unsigned long prevMillis_RED = 0;
unsigned long interval_RED_H = 800;
unsigned long interval_RED_L = 200;
unsigned long interval_RED = interval_RED_L;

bool ledState_YEL = LOW;
unsigned long prevMillis_YEL = 0;
unsigned long interval_YEL_H = 2800;
unsigned long interval_YEL_L = 200;
unsigned long interval_YEL = interval_YEL_L;

bool ledState_BLU = LOW;
unsigned long prevMillis_BLU = 0;
unsigned long interval_BLU_H = 8800; 
unsigned long interval_BLU_L = 200; 
unsigned long interval_BLU = interval_BLU_L;

unsigned long currMillis_ALL = 0;


void setup() {
  // Set the pin directions for LEDs
  pinMode(RED_LED, OUTPUT);
  pinMode(YEL_LED, OUTPUT);
  pinMode(BLU_LED, OUTPUT);
}

void loop() {

  // Store the currently time
  // Notice: it use a single current time for synchonization with other function
  currMillis_ALL = millis();

  process_RED();
  process_YEL();
  process_BLU();

}

void process_RED() {
  if (currMillis_ALL - prevMillis_RED >= interval_RED) {
    // Elapse time has reached the interval
    // Save the current time as previous time
    prevMillis_RED = currMillis_ALL;

    // toggle LED state
    if (ledState_RED == HIGH) {
      ledState_RED = LOW;
      interval_RED = interval_RED_L;
    } else {
      ledState_RED = HIGH;
      interval_RED = interval_RED_H;
    }
    
    digitalWrite(RED_LED, ledState_RED);
  }
}

void process_YEL() {
  if (currMillis_ALL - prevMillis_YEL >= interval_YEL) {
    // Elapse time has reached the interval
    // Save the current time as previous time
    prevMillis_YEL = currMillis_ALL;

    // toggle LED state
    if (ledState_YEL == HIGH) {
      ledState_YEL = LOW;
      interval_YEL = interval_YEL_L;
    } else {
      ledState_YEL = HIGH;
      interval_YEL = interval_YEL_H;
    }
    
    digitalWrite(YEL_LED, ledState_YEL);
  }
}

void process_BLU() {
  if (currMillis_ALL - prevMillis_BLU >= interval_BLU) {
    // Elapse time has reached the interval
    // Save the current time as previous time
    prevMillis_BLU = currMillis_ALL;

    // toggle LED state
    if (ledState_BLU == HIGH) {
      ledState_BLU = LOW;
      interval_BLU = interval_BLU_L;
    } else {
      ledState_BLU = HIGH;
      interval_BLU = interval_BLU_H;
    }
    
    digitalWrite(BLU_LED, ledState_BLU);
  }
}

I hope you find it useful and helpful. If you have any question, please do not hesitate to write it in the comment box.

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