const int buttonPin = 2;
const int pc817ControlPin = 3;

void setup() {
  pinMode(buttonPin, INPUT);
  pinMode(pc817ControlPin, OUTPUT);
}

void loop() {
  int buttonState = digitalRead(buttonPin);
  if (buttonState == HIGH) {
    digitalWrite(pc817ControlPin, HIGH); // Turn ON PC817
  } else {
    digitalWrite(pc817ControlPin, LOW);  // Turn OFF PC817
  }
}