16x2 LCD without I2C on Arduino Uno — 4-bit wiring and contrast

Before I2C backpacks, every Arduino book wired the 16×2 LCD this way, and many kits sold in India still ship it bare. It needs six signal wires in 4-bit mode, plus power, contrast and backlight. The built-in LiquidCrystal library drives it.

On the Uno this takes six digital pins. The sketch uses the same pins as the Arduino IDE examples (RS on D12, E on D11, data on D5–D2), so you can follow any old tutorial. Everything is 5 V, so no shifting is needed. The one part that needs care is contrast on V0. A fixed 1 kΩ resistor to GND works for most panels; a 10 kΩ pot lets you tune it.

The sketch prints a greeting on the first line and counts seconds on the second.

Wiring

Board quirks

• D0–D3 on the LCD stay unconnected — 4-bit mode sends each byte in two halves over D4–D7.
• These are the pins from the Arduino IDE’s LiquidCrystal examples. They use 6 Uno pins including D3, D5 and D11 — three of the six PWM pins, and D11 is also SPI MOSI. If you need those, move them: any digital pin works, just change the numbers in the constructor.
• Short on pins? An I2C backpack does the same job on two wires — see the 16x2 I2C guide.
• Contrast is the first thing to fix. With V0 floating you get nothing; tied straight to GND you get dark blocks on the top row.

Code

// 16x2 LCD (HD44780, no I2C backpack) on an Arduino Uno R3 in 4-bit mode.
// RS → D12, E → D11, D4 → D5, D5 → D4, D6 → D3, D7 → D2 (the Arduino IDE example pins).
// VSS, RW, K → GND. VDD → 5V. A → 220 Ω → 5V. V0 → about 1 kΩ to GND (or a 10 kΩ pot wiper).
#include <LiquidCrystal.h>

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);  // RS, E, D4, D5, D6, D7

void setup() {
  Serial.begin(9600);
  lcd.begin(16, 2);
  lcd.print(F("Hello, Uno!"));
  Serial.println(F("LCD started in 4-bit mode. No text? Adjust V0 (contrast)."));
}

void loop() {
  lcd.setCursor(0, 1);
  lcd.print(F("Up "));
  lcd.print(millis() / 1000);
  lcd.print(F(" s     "));
  delay(1000);
}

// 16x2 LCD (HD44780, no I2C backpack) on an Arduino Uno R3 in 4-bit mode.
// RS → D12, E → D11, D4 → D5, D5 → D4, D6 → D3, D7 → D2 (the Arduino IDE example pins).
// VSS, RW, K → GND. VDD → 5V. A → 220 Ω → 5V. V0 → about 1 kΩ to GND (or a 10 kΩ pot wiper).
#include <LiquidCrystal.h>

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);  // RS, E, D4, D5, D6, D7

void setup() {
  Serial.begin(9600);
  lcd.begin(16, 2);
  lcd.print(F("Hello, Uno!"));
  Serial.println(F("LCD started in 4-bit mode. No text? Adjust V0 (contrast)."));
}

void loop() {
  lcd.setCursor(0, 1);
  lcd.print(F("Up "));
  lcd.print(millis() / 1000);
  lcd.print(F(" s     "));
  delay(1000);
}

Library: LiquidCrystal (Arduino, Adafruit) — compiled with LiquidCrystal 1.0.7.

Expected serial output

LCD started in 4-bit mode. No text? Adjust V0 (contrast).

LCD started in 4-bit mode. No text? Adjust V0 (contrast).

Common errors