#include <Adafruit_NeoPixel.h>
#define PIN        8
#define NUMPIXELS 16
Adafruit_NeoPixel pixels(NUMPIXELS, PIN, NEO_GRB + NEO_KHZ800);

void setup() {
  pixels.begin(); // INITIALIZE NeoPixel strip object (REQUIRED)
  pixels.clear(); // Set all pixel colors to 'off'
  pixels.show();  // Send the updated pixel colors to the hardware.
  pinMode(A0, INPUT);
  Serial.begin(9600);
}

void loop() {
  int data = analogRead(A0);
  float resolution = 5.0 / 1023 ;
  float volt = data * resolution ;
  Serial.print("Data = " + String(data));
  Serial.println("\t Volt= " + String(volt));
  pixels.clear(); // Set all pixel colors to 'off'
  pixels.show();  // Send the updated pixel colors to the hardware.

  float d = 5.0 / 16 ; // delta = 1.25v
  int n = volt / d ;  // LED number
  pixels.setPixelColor(n, pixels.Color(255, 255, 0)); // R G B - 0 .. 255
  pixels.show();   // Send the updated pixel colors to the hardware.
  delay(100);
}