int OPTOSWITCH_PIN = 2; const int LED_PIN = 7; void setup() { pinMode(LED_PIN, OUTPUT); Serial.begin(115200); } void loop() { if (digitalRead(OPTOSWITCH_PIN) == 0) { // There is no obstacle between emitter and sensor digitalWrite(LED_PIN, HIGH); Serial.println("H"); } else { digitalWrite(LED_PIN, LOW); Serial.println("L"); } delay(10); }