#include <Adafruit_NeoPixel.h>

#define ADC_PIN 34
#define LED_PIN 18

#define ADC_CONVERSION 4095.0

#define LED_COUNT (16 * 2)
Adafruit_NeoPixel strip(LED_COUNT, LED_PIN, NEO_GRB + NEO_KHZ800);

void setup()
{
  pinMode(ADC_PIN, INPUT);
  pinMode(LED_PIN, OUTPUT);
  
  strip.begin();
  strip.show();
  strip.setBrightness(255);
}

void loop()
{
  float inVolt = (float) analogRead(ADC_PIN) / ADC_CONVERSION;

  drawNeoBar(inVolt * strip.numPixels(), strip.Color(inVolt * 255, 0, 255 - inVolt * 255));

  delay(10);
}

void drawNeoBar(int pixelEnd, uint32_t color)
{
  for(int i = 0; i < pixelEnd; i++) {
    strip.setPixelColor(i, color);
    strip.show();
  }

  for(int i = pixelEnd + 1; i < strip.numPixels(); i++) {
    strip.setPixelColor(i, strip.Color(0, 0, 0));
    strip.show();
  }
  if (!pixelEnd)
  {
    strip.setPixelColor(0, strip.Color(0, 0, 0));
  }
}