multitasking_demo.ino

/*
 *   multitasking_demo
 *   A sketch written to help people understand how to implement basic multitasking on the Arduino
 *   Written by Peter Dalmaris, April 21 2016.
 *   Arduino Tips and Tricks
 *   txplore.com
 *
 *   Requirements: An Arduino, two LEDs, two 220Ohm resistors, a breadboard, wires.
 *   Play around with the variables in lines 18 to 26 to create different light show patterns. 
 */

const int       ledPinA         = 9;    // the number of the LED A pin
const int       ledPinB         = 8;    // the number of the LED B pin
int             ledStateA       = LOW;  // ledState used to set the LEDA
int             ledStateB       = LOW;  // ledState used to set the LEDB
unsigned long   previousMillisA = 0;    // will store last time was updated for LEDA
unsigned long   previousMillisB = 0;    // will store last time was updated for LEDB
const long      start_cycle_A   = 0;    // This is the start of the ON/OFF cycle for LEDA
const long      start_cycle_B   = 100;    // This is the start of the ON/OFF cycle for LEDB,
                                        // set to 5ms after the start of LEDA cycle.
                                        // You can also think of these variables as the offset
                                        // from the millis "start". 
const long      intervalA_ON    = 500;  // interval at which to turn LEDA ON (milliseconds)
const long      intervalA_OFF   = 700;  // interval at which to turn LEDA OFF (milliseconds)
const long      intervalB_ON    = 98;   // interval at which to turn LEDB ON (milliseconds)
const long      intervalB_OFF   = 250;  // interval at which to turn LEDB OFF (milliseconds)

void setup() {
  pinMode(ledPinA, OUTPUT);
  pinMode(ledPinB, OUTPUT);
}

void loop() {
  unsigned long currentMillis   = millis();

  // Is it time start the LEDA cycle? If yes, turn the LED on 
  // and update the previousMillisA variable.
  if (ledStateA == LOW && (currentMillis - previousMillisA >= intervalA_OFF + start_cycle_A)) {
    previousMillisA             = currentMillis;  
    ledStateA                   = HIGH; 
    digitalWrite(ledPinA, ledStateA);
  }

  // Is it time to turn LEDA off? if yes, turn it off an update the previousMillisA variable
  if (ledStateA == HIGH && (currentMillis - previousMillisA >= intervalA_ON + start_cycle_A)) {
    previousMillisA             = currentMillis;  
    ledStateA                   = LOW;  
    digitalWrite(ledPinA, ledStateA);
  }

  // Is it time start the LEDB cycle? If yes, turn the LED on 
  // and update the previousMillisB variable.
  if (ledStateB == LOW && (currentMillis - previousMillisB >= intervalA_OFF + start_cycle_B)) {
    previousMillisB             = currentMillis;  
    ledStateB                   = HIGH; 
    digitalWrite(ledPinB, ledStateB);
  }
  
  // Is it time to turn LEDB off? if yes, turn it off an update the previousMillisB variable
  if (ledStateB == HIGH && (currentMillis - previousMillisB >= intervalA_ON + start_cycle_B)) {
    previousMillisB             = currentMillis;  
    ledStateB                   = LOW;  
    digitalWrite(ledPinB, ledStateB);
  }
  
}