#define redled            4
int ledState = LOW;
unsigned long previousMillis = 0; 
const long interval = 1000; 

void setup() {
  // put your setup code here, to run once:

}

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

  if (currentMillis - previousMillis >= interval) {
    // save the last time you blinked the LED
    previousMillis = currentMillis;

    // if the LED is off turn it on and vice-versa:
    if (ledState == LOW) {
      ledState = HIGH;
    } else {
      ledState = LOW;
    }

    // set the LED with the ledState of the variable:
    digitalWrite(redled, ledState);
  }


}