int readPin=A3;
int readVal;
float V2=0;
int delayTime=500;
int redLED=2;
float Vh=3.5;
float Vl=1.5;

void setup() {
  // put your setup code here, to run once:
pinMode(readPin, INPUT);
pinMode(redLED, OUTPUT);
Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
readVal=analogRead(readPin);
V2=(5./1023.)*readVal;
Serial.println(V2);

if (V2 > Vl && V2 < Vh) {
  digitalWrite(redLED,HIGH);
}
if (V2 < Vl || V2 > Vh) {
  digitalWrite(redLED,LOW);
}
delay(delayTime);
}