Why displays the Esp32 "nan" when using logarithem?

Question

I´m building a weather staion with an Esp32 and a thermal resister. I want to display the value in Celsius. For the calculation i need the logarithem but when i use it, it always display "nan".

int ThermistorPin = 27;
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() {
Serial.begin(115200);
}

void loop() {

  Vo = analogRead(A0);

  R2 = R1 * (1023.0 / (float)Vo - 1.0);
  logR2 = log(R2);
  Serial.println(logR2);
  T = (1.0 / (c1 + c2*logR2 + c3*logR2*logR2*logR2));
  Tc = T - 273.15;

  Serial.print("Temperature: "); 
  Serial.print(Tc);
  Serial.println(" C");   

  delay(500);
}

Answer 1

I am not a mathematician, but the problem lies with the number 1023. That's the 10 bit resolution used by most Arduino's (Uno, Mega). The ESP32 has a resolution of 12 bits, which gives the number 4095. So, replace 1023 by 4095, because the ESP32 will generates numbers above 1023, up to 4095.

R2 = R1 * (4095/ (float)Vo - 1.0);

A small tip: c3*logR2*logR2*logR2 can be written as c3*pow(logR2 ,3)