/*

  Forum: https://forum.arduino.cc/t/millis-instead-of-delay-and-loop-instead-of-for-loop/1110044/24
  Wokwi: https://wokwi.com/projects/372857069603319809

*/

unsigned long readTime = 0;
const unsigned long period = 1000;
const byte ledPin = 13;
bool secondRead = false;

void setup()
{
  Serial.begin(115200);
  pinMode(ledPin, OUTPUT);
}
void loop()
{
  if (millis() - readTime >= period)
  {
    if ( secondRead == true) {
      digitalWrite(ledPin, !digitalRead(ledPin));
    }
    secondRead = !secondRead;
    readTime = millis();
  }
}