Warm-hands meter on an Arduino Uno

// Warm-hands meter: a TMP36 temperature sensor and three LEDs that light one
// by one as the sensor warms up.
//
//   TMP36   left leg (flat side toward you) -> 5V, middle -> A0, right -> GND
//   pin 2, 3, 4   the three LEDs, each through 220 ohm to GND
//
// The TMP36 gives 0.5 V at 0 C and 10 mV more for every degree, so
//   volts   = reading * 5.0 / 1024
//   celsius = (volts - 0.5) * 100
//
// The room is the baseline: 22 C here. Set BASELINE to what the serial
// monitor reads in your room before you touch the sensor. Then squeeze the
// sensor between your fingers and it climbs toward skin temperature: two
// degrees over the baseline lights the first LED, four the second, six the
// third.

const int SENSOR = A0;
const float BASELINE = 22.0;  // the room: change it to what yours reads

const int LEDS[3] = {2, 3, 4};

void setup() {
  for (int i = 0; i < 3; i++) pinMode(LEDS[i], OUTPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: warm-hands meter");
}

void loop() {
  int reading = analogRead(SENSOR);
  float volts = reading * 5.0 / 1024.0;
  float celsius = (volts - 0.5) * 100.0;

  Serial.print("reading ");
  Serial.print(reading);
  Serial.print(", volts ");
  Serial.print(volts, 2);
  Serial.print(", degrees C ");
  Serial.println(celsius, 1);

  int lit = 0;
  if (celsius >= BASELINE + 2) lit = 1;
  if (celsius >= BASELINE + 4) lit = 2;
  if (celsius >= BASELINE + 6) lit = 3;
  for (int i = 0; i < 3; i++) digitalWrite(LEDS[i], i < lit ? HIGH : LOW);

  delay(250);
}