#define PIN 0
#define K1  421.0
#define K2  751.0

uint32_t time_high, time_low, last_time, new_time;
float temperature;

void setup() {
  Serial.begin(12345);
  pinMode(PIN, INPUT);
  new_time = last_time = micros();
}

void loop() {
  while(digitalRead(PIN));
  new_time = micros();
  time_high = new_time - last_time;
  last_time = new_time;
  while(!digitalRead(PIN));
  new_time = micros();
  time_low = new_time - last_time;
  last_time = new_time;
  temperature = K1 - (K2 * time_high) / (float)time_low;
  Serial.print(time_low);  Serial.print("  ");
  Serial.print(time_high);  Serial.print("  ");
  Serial.println(temperature);
}