Distance rainbow on an Arduino Uno

// Distance rainbow: a Sharp GP2Y0A21 and an eight-LED WS2812 stick.
//
//   A0      the sensor's VO (yellow); VCC and GND from the rails
//   pin 6   the stick's DIN
//
// SharpIR turns the sensor's voltage into centimeters, 10 to 80 (and 9 or 81
// past either end, as the real library answers). The nearer
// the hand, the more of the stick lights: none at 80 cm, all eight at 10, and
// each LED's color runs from green at the start of the stick to red at the
// end, so a close hand is a red warning.
//
// The sensor only measures every 38 ms, and reads a hand closer than 10 cm
// as further away, which is why the stick never quite fills when the hand is
// pressed right up against it.

#include <Adafruit_NeoPixel.h>
#include <SharpIR.h>

const int LEDS = 8;
const int STRIP_PIN = 6;

Adafruit_NeoPixel strip(LEDS, STRIP_PIN, NEO_GRB + NEO_KHZ800);
SharpIR sensor(SharpIR::GP2Y0A21YK0F, A0);

int lastCm = -1;

void setup() {
  Serial.begin(115200);
  Serial.println("Mokxi Arduino Uno: distance rainbow");
  strip.begin();
  strip.setBrightness(80);
  strip.show();
}

void loop() {
  int cm = sensor.getDistance();
  // 80 cm lights none, 10 cm all eight.
  int lit = (int)((80L - cm) * LEDS / 70);
  if (lit < 0) lit = 0;
  if (lit > LEDS) lit = LEDS;
  for (int i = 0; i < LEDS; i++) {
    if (i < lit) {
      // Green to red along the stick.
      int red = i * 255 / (LEDS - 1);
      strip.setPixelColor(i, strip.Color(red, 255 - red, 0));
    } else {
      strip.setPixelColor(i, 0);
    }
  }
  strip.show();
  if (cm != lastCm) {
    lastCm = cm;
    Serial.print(cm);
    Serial.print(" cm: ");
    Serial.print(lit);
    Serial.println(" lit");
  }
  delay(50);
}