int ThermistorPin = 3;
int LED = 7;
int Vo;
float R1 = 10000;
float logR2, R2, T, Tc, Tf;
float c1 = 1.009249522e-03, c2 = 2.378405444e-04, c3 = 2.019202697e-07;

void setup() {
pinMode(LED, OUTPUT);
pinMode(ThermistorPin, INPUT);
}

void loop() {

  Vo = analogRead(ThermistorPin);
  R2 = R1 * (1023.0 / (float)Vo - 1.0);
  logR2 = log(R2);
  T = (1.0 / (c1 + c2*logR2 + c3*logR2*logR2*logR2));
  Tc = T - 273.15;
  Tf = (Tc * 9.0)/ 5.0 + 32.0; 
  if (Tc >= 20  && Tc <= 23)
  {digitalWrite(LED, HIGH);
  delay(1000);
  digitalWrite(LED, LOW);}
  else 
  {digitalWrite(LED, LOW);}
  delay(500);
}