int crvena=13;
int zolta=11;
int zelena=9;
int pot= A3;
int broj;
float U;

void setup() {
  Serial.begin(9600);
  pinMode(pot, INPUT);
  pinMode(crvena, OUTPUT);
  pinMode(zolta, OUTPUT);
  pinMode(zelena, OUTPUT);

}

void loop() {
  broj = analogRead(pot);
  U=(5./1023.)*broj;
  Serial.println(U);
 if (U>=4){
   digitalWrite(crvena, HIGH);
   digitalWrite(zelena, LOW);
   digitalWrite(zolta, LOW);
 }
 else if(U<4 && U>=2.5){
   digitalWrite(crvena, LOW);
   digitalWrite(zelena, LOW);
   digitalWrite(zolta, HIGH);
 }
 else{
   digitalWrite(crvena, LOW);
   digitalWrite(zelena, HIGH);
   digitalWrite(zolta, LOW);
 }
  
}