// ldr arduino - SEECS
 
 void setup()  
 {  
 Serial.begin(9600); // sensor buart rate  
 pinMode(4,OUTPUT); // led pin  
 }  
 void loop()  
 {  
 int s1=analogRead(A0); // LDR Sensor output pin connected  
 Serial.println(s1);  
 delay(1000);  
 if(s1< 500 )  
 {  
 digitalWrite(4,HIGH); // led ON  
 }  
 else  
 {  
 digitalWrite(4,LOW); // Red led OFF  
 }  
 }