Love meter on an Arduino Uno

// Love meter: hold the temperature sensor between your fingers and a bar of
// ten LEDs fills up with your warmth. The warmer your hands, the more love.
//
//   TMP36     VS -> 5 V, VOUT -> A0, GND -> GND
//   LED bar   10 WS2812B LEDs, DIN <- 330 ohms <- pin 6, VDD -> 5 V, VSS -> GND
//
// It is the classic love-o-meter, honest about what it measures: the TMP36
// gives 10 mV per degree Celsius, with 500 mV at 0 degrees, so
// degrees = (millivolts - 500) / 10. For the first two seconds the sketch
// reads the room and keeps that as the baseline. After that, every half a
// degree above the room lights one more LED, from pink up to deep red.
//
// A hand warms the sensor slowly, over ten or twenty seconds, because the
// little plastic package has to heat up. That slow climb is the fun part.
//
// Things to try. Drag the sensor's temperature up. Change STEP_TENTHS to make
// the meter harder or easier to fill.

#include <Adafruit_NeoPixel.h>

const int BAR_PIN = 6;
const int LEDS = 10;
const int STEP_TENTHS = 5;   // tenths of a degree per LED

Adafruit_NeoPixel bar(LEDS, BAR_PIN, NEO_GRB + NEO_KHZ800);

const char *LABELS[] = {"Just friends", "A little crush", "Sweet on you", "Smitten",
                        "Head over heels", "True love!"};

long room = 0;   // tenths of a degree
int lastLevel = -1;

long tenths() {
  long mv = analogRead(A0) * 5000L / 1024;
  return mv - 500;   // 10 mV a degree is 1 mV a tenth
}

void setup() {
  Serial.begin(9600);
  bar.begin();
  bar.setBrightness(150);
  bar.show();
  long sum = 0;
  for (int i = 0; i < 20; i++) {
    sum += tenths();
    delay(100);
  }
  room = sum / 20;
  Serial.print("Love meter ready. The room is ");
  Serial.print(room / 10);
  Serial.print(".");
  Serial.print(abs(room % 10));
  Serial.println(" C. Hold the sensor!");
}

void loop() {
  long warmer = tenths() - room;
  int level = constrain(warmer / STEP_TENTHS, 0, LEDS);
  for (int i = 0; i < LEDS; i++) {
    if (i < level) {
      // Pink at the bottom, deep red at the top.
      bar.setPixelColor(i, 255, 100 - i * 10, 140 - i * 14);
    } else {
      bar.setPixelColor(i, 0, 0, 0);
    }
  }
  bar.show();
  if (level != lastLevel) {
    lastLevel = level;
    Serial.print("Level ");
    Serial.print(level);
    Serial.print(": ");
    Serial.println(LABELS[level * 5 / LEDS]);
  }
  delay(200);
}