#include "FastLED.h"

#define PIN_SLIDE_POT_A A0 // input pin of the slide pot
#define MAX_SLIDE_POT_ANALGOG_READ_VALUE 700 // maximum voltage as analog-to-digital converted value, depends on the voltage level of the VCC pin. Examples: 5V = 1023; 3.3V ~700

#define NUM_LEDS 10 // add number of LEDs of your RGB LED strip
#define PIN_LED 3 // digital output PIN that is connected to DIN of the RGB LED strip
#define LED_COLOR CRGB::DarkOrchid // see https://github.com/FastLED/FastLED/wiki/Pixel-reference for a full list, e.g. CRGB::AliceBlue, CRGB::Amethyst, CRGB::AntiqueWhite...

CRGB rgb_led[NUM_LEDS]; // color array of the LED RGB strip

void setup() {
  Serial.begin(9600);

  pinMode(PIN_SLIDE_POT_A, INPUT);
  FastLED.addLeds<WS2812B, PIN_LED>(rgb_led, NUM_LEDS);

  Serial.println("Setup done.");
}

void loop() {
  // 1) Analog value of slide pot is read
  int value_slide_pot_a = analogRead(PIN_SLIDE_POT_A);
  Serial.print("Slide Pot value: ");
  Serial.println(value_slide_pot_a);

  // 2) Analog value is mapped from slide pot range (analog input value) to led range (number of LEDs)
  int num_leds_switchedon = map(value_slide_pot_a, 0, MAX_SLIDE_POT_ANALGOG_READ_VALUE, 0, NUM_LEDS);


  // 3) Light up the LEDs
  // Only LEDs are switched on which correspond to the area left of the slide knob
  for (int i = 0; i < num_leds_switchedon; ++i) {
    rgb_led[i] = LED_COLOR;
  }
  // LEDs are switched off which correspond to the area right of the slide knob
  for (int i = num_leds_switchedon; i < NUM_LEDS; ++i) {
    rgb_led[i] = CRGB::Black;
  }
  FastLED.show();
}