16x2 I2C LCD with NodeMCU ESP8266 — 5 V wiring and code

A 16x2 LCD with an I2C backpack needs only two signal wires, which suits the NodeMCU’s small number of free pins. The complication is voltage: the LCD wants 5 V for good contrast, and the ESP8266 is a 3.3 V chip.

So the LCD is powered from VIN, and a small BSS138 level shifter sits between D2/D1 and the backpack’s SDA/SCL. The sketch prints an uptime clock and a custom degree symbol, ready for a temperature display.

Wiring

Board quirks

• The PCF8574 backpack pulls SDA and SCL up to its own VCC — 5 V here. ESP8266 pins are not specified for 5 V, so the level shifter keeps them at 3.3 V. (Wiring straight across often “works”; it is still outside the chip’s ratings.)
• Run at 3.3 V instead and most 5 V LCDs show faint or no characters even with the contrast pot turned fully. Buy a 3.3 V LCD if you want to skip the shifter.
• lcd.init() calls Wire.begin() for you, which on the ESP8266 means SDA = D2 and SCL = D1. To use other pins, call Wire.begin(sda, scl) before lcd.init() — but not D0, which can’t do I2C, and not D8, which the pull-ups would hold high at boot.
• Arduino IDE warns that LiquidCrystal I2C “claims to run on avr architecture”. It is only a warning; the library works on the ESP8266.

Code

// 16x2 LCD with PCF8574 I2C backpack on a NodeMCU (ESP8266).
// VCC → VIN (5 V), GND → GND, SDA → level shifter → D2 (GPIO4), SCL → level shifter → D1 (GPIO5).
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 16, 2);  // 0x3F on backpacks with the PCF8574A chip
byte degree[8] = {0b00110, 0b01001, 0b01001, 0b00110, 0b00000, 0b00000, 0b00000, 0b00000};

void setup() {
  Serial.begin(115200);
  Serial.println();
  lcd.init();  // calls Wire.begin(): SDA = D2, SCL = D1 on the ESP8266
  lcd.backlight();
  lcd.createChar(0, degree);
  lcd.setCursor(0, 0);
  lcd.print("NodeMCU + LCD");
  Serial.println("LCD at 0x27 - if the screen stays blank, turn the blue contrast pot");
}

void loop() {
  unsigned long s = millis() / 1000;
  char line[17];
  snprintf(line, sizeof line, "Up %02lu:%02lu:%02lu", s / 3600, (s / 60) % 60, s % 60);
  lcd.setCursor(0, 1);
  lcd.print(line);
  lcd.print(' ');
  lcd.write(byte(0));  // custom degree symbol, just to show createChar works
  Serial.println(line);
  delay(1000);
}

// 16x2 LCD with PCF8574 I2C backpack on a NodeMCU (ESP8266).
// VCC → VIN (5 V), GND → GND, SDA → level shifter → D2 (GPIO4), SCL → level shifter → D1 (GPIO5).
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 16, 2);  // 0x3F on backpacks with the PCF8574A chip
byte degree[8] = {0b00110, 0b01001, 0b01001, 0b00110, 0b00000, 0b00000, 0b00000, 0b00000};

void setup() {
  Serial.begin(115200);
  Serial.println();
  lcd.init();  // calls Wire.begin(): SDA = D2, SCL = D1 on the ESP8266
  lcd.backlight();
  lcd.createChar(0, degree);
  lcd.setCursor(0, 0);
  lcd.print("NodeMCU + LCD");
  Serial.println("LCD at 0x27 - if the screen stays blank, turn the blue contrast pot");
}

void loop() {
  unsigned long s = millis() / 1000;
  char line[17];
  snprintf(line, sizeof line, "Up %02lu:%02lu:%02lu", s / 3600, (s / 60) % 60, s % 60);
  lcd.setCursor(0, 1);
  lcd.print(line);
  lcd.print(' ');
  lcd.write(byte(0));  // custom degree symbol, just to show createChar works
  Serial.println(line);
  delay(1000);
}

Library: LiquidCrystal I2C (Frank de Brabander) — compiled with LiquidCrystal I2C 1.1.2.

Expected serial output

LCD at 0x27 - if the screen stays blank, turn the blue contrast pot
Up 00:00:00
Up 00:00:01
Up 00:00:02

LCD at 0x27 - if the screen stays blank, turn the blue contrast pot
Up 00:00:00
Up 00:00:01
Up 00:00:02

Common errors