Distance meter with light bar

// Distance meter with light bar
// The closer you get, the more lights turn on: green, then orange, then red.

#include <Adafruit_NeoPixel.h>

const int TRIG_PIN = 9;     // Trig of the HC-SR04 on pin 9
const int ECHO_PIN = 10;    // Echo of the HC-SR04 on pin 10
const int RING_PIN = 6;     // DI of the LED ring on pin 6
const int NUM_LEDS = 8;
const int MAX_DISTANCE = 80; // Farther than this (in cm): all lights off

Adafruit_NeoPixel ring(NUM_LEDS, RING_PIN, NEO_GRB + NEO_KHZ800);

long measureDistance() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  long time = pulseIn(ECHO_PIN, HIGH, 30000);
  if (time == 0) return 999;
  return time / 58;
}

void setup() {
  Serial.begin(9600);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  ring.begin();
  ring.setBrightness(40);
  ring.show();
}

void loop() {
  long distance = measureDistance();
  Serial.print(F("Distance: "));
  Serial.print(distance);
  Serial.println(F(" cm"));

  // How many lights should turn on? Close = 8, far away = 0
  int count = map(constrain(distance, 0, MAX_DISTANCE), 0, MAX_DISTANCE, NUM_LEDS, 0);

  for (int i = 0; i < NUM_LEDS; i++) {
    if (i < count) {
      if (i < 3)      ring.setPixelColor(i, ring.Color(0, 255, 0));    // Green
      else if (i < 6) ring.setPixelColor(i, ring.Color(255, 120, 0));  // Orange
      else            ring.setPixelColor(i, ring.Color(255, 0, 0));    // Red
    } else {
      ring.setPixelColor(i, 0);                                        // Off
    }
  }
  ring.show();
  delay(100);
}