int lightPin = 0; //define a pin for Photo resistor int threshold = 17; void setup(){ Serial.begin(9600); //Begin serial communcation pinMode(13, OUTPUT); pinMode(A0, INPUT_PULLUP); } void loop(){ Serial.println(analogRead(lightPin)); if(analogRead(lightPin) > threshold ){ digitalWrite(13, LOW); Serial.println("LOW"); }else{ digitalWrite(13, HIGH); Serial.println("high"); } delay(100); }