const int ledPin = LED_BUILTIN;  
int ledState = LOW;

unsigned long previousMillis = 0;
const long interval = 1000;

void setup() {
    pinMode(ledPin, OUTPUT);
}

void loop() {

unsigned long currentMillis = millis();

if (currentMillis - previousMillis >= interval) {
previousMillis = currentMillis;
if (ledState == LOW) {
ledState = HIGH;
} else 
{
ledState = LOW;
}
digitalWrite(ledPin, ledState);
}
 }


