triple-blink.c

#include <Arduino.h>

#define PIN_LED_A 13
#define PIN_LED_B 12
#define PIN_LED_C 11

#define LED_A_STATE_SWITCH_INTERVAL 500  // milliseconds between LED state change
#define LED_B_STATE_SWITCH_INTERVAL 300  // milliseconds between LED state change
#define LED_C_STATE_SWITCH_INTERVAL 200  // milliseconds between LED state change

unsigned long ledNextStateFlipA = 0, ledNextStateFlipB = 0, ledNextStateFlipC = 0;
uint8_t ledStateA = LOW, ledStateB = LOW, ledStateC = LOW;

void setup(void) {
    pinMode(PIN_LED_A, OUTPUT);
    digitalWrite(PIN_LED_A, LOW);
    pinMode(PIN_LED_B, OUTPUT);
    digitalWrite(PIN_LED_B, LOW);
    pinMode(PIN_LED_C, OUTPUT);
    digitalWrite(PIN_LED_C, LOW);
}

void loop(void) {
    if (millis() > ledNextStateFlipA) {
        ledNextStateFlipA = millis() + LED_A_STATE_SWITCH_INTERVAL;
        ledStateA = (ledStateA == LOW ? HIGH : LOW);
        digitalWrite(PIN_LED_A, ledStateA);
    }
    if (millis() > ledNextStateFlipB) {
        ledNextStateFlipB = millis() + LED_B_STATE_SWITCH_INTERVAL;
        ledStateB = (ledStateB == LOW ? HIGH : LOW);
        digitalWrite(PIN_LED_B, ledStateB);
    }
    if (millis() > ledNextStateFlipC) {
        ledNextStateFlipC = millis() + LED_C_STATE_SWITCH_INTERVAL;
        ledStateC = (ledStateC == LOW ? HIGH : LOW);
        digitalWrite(PIN_LED_C, ledStateC);
    }
}