Thermistor thermometer on an Arduino Uno

// Thermistor thermometer: a 10k thermistor on A0, the temperature on an LCD.
//
//   10k resistor   5V -> A0
//   thermistor     A0 -> GND
//   LCD            RS 12, E 11, D4 to D7 on 5, 4, 3, 2, as in the LCD lesson
//
// A thermistor is a resistor that changes with temperature: this kind (NTC)
// has 10k at 25 C and less when it is warmer. With the fixed 10k above it,
// the two make a voltage divider, and A0 reads where the middle sits.
//
// From the reading back to degrees takes two steps:
//   1. resistance:  R = 10000 * reading / (1023 - reading)
//   2. temperature: the beta equation, 1/T = 1/T0 + ln(R / R0) / B, with T0
//      = 298.15 K (25 C), R0 = 10000 and B = 3950 from the datasheet.

#include <LiquidCrystal.h>

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

const float BETA = 3950.0;
const float R_FIXED = 10000.0;
const float R_25C = 10000.0;

void setup() {
  lcd.begin(16, 2);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: thermistor thermometer");
}

void loop() {
  int reading = analogRead(A0);
  if (reading <= 0 || reading >= 1023) {
    lcd.setCursor(0, 0);
    lcd.print("Check wiring    ");
    delay(500);
    return;
  }
  float ohms = R_FIXED * reading / (1023.0 - reading);
  float kelvin = 1.0 / (1.0 / 298.15 + log(ohms / R_25C) / BETA);
  float celsius = kelvin - 273.15;
  float fahrenheit = celsius * 9.0 / 5.0 + 32.0;

  lcd.setCursor(0, 0);
  lcd.print("Temp ");
  lcd.print(celsius, 1);
  lcd.print(" C   ");
  lcd.setCursor(0, 1);
  lcd.print("     ");
  lcd.print(fahrenheit, 1);
  lcd.print(" F   ");

  Serial.print("temperature ");
  Serial.print(celsius, 1);
  Serial.println(" C");
  delay(500);
}