Analog control with a knob

/*
  04 — Analog control with a knob
  Boards: ESP32 or NodeMCU V3 ESP8266 development board — same sketch, and the point is the difference.
  Parts: potentiometer, LCD 1602 (I2C backpack).
  Library: "LiquidCrystal I2C" by Frank de Brabander.

  Wiring:
    Potentiometer: outer legs -> 3V3 and GND, middle (wiper) -> ESP32 GPIO 35 / NodeMCU A0
    LCD (I2C):     VCC -> VIN (5 V), GND -> GND, SDA -> ESP32 GPIO 21 / NodeMCU D2,
                   SCL -> ESP32 GPIO 22 / NodeMCU D1

  ESP32: several 12-bit ADC inputs (0..4095). NodeMCU: exactly one, A0, 10-bit
  (0..1023). And NodeMCU's D-labels are not GPIO numbers. Those two facts explain
  most sketches that work on one board and misbehave on the other.
*/

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

#if defined(ESP32)
  const int POT_PIN = 35;       // ADC1 — keeps working when WiFi is on
  const int ADC_MAX = 4095;
#elif defined(ESP8266)
  const int POT_PIN = A0;
  const int ADC_MAX = 1023;
#else
  #error "Select an ESP32 or ESP8266 board"
#endif

LiquidCrystal_I2C lcd(0x27, 16, 2);   // if the LCD stays blank, try 0x3F

void setup() {
  Serial.begin(115200);
  lcd.init();
  lcd.backlight();
  lcd.print("Turn the knob");
}

void loop() {
  int raw = analogRead(POT_PIN);
  int percent = map(raw, 0, ADC_MAX, 0, 100);

  lcd.setCursor(0, 0);
  lcd.print("raw: "); lcd.print(raw); lcd.print("    ");
  lcd.setCursor(0, 1);
  lcd.print("level: "); lcd.print(percent); lcd.print("%   ");

  // Bar graph on the right of line 2: 0..5 blocks
  lcd.setCursor(11, 1);
  int blocks = map(raw, 0, ADC_MAX, 0, 5);
  for (int i = 0; i < 5; i++) lcd.print(i < blocks ? "\xFF" : " ");

  delay(100);
}