Day 15: LCD Screen — Hello Anish!

Hi Anish! Until now, Arduino has only been able to talk back to you through the Serial Monitor on your laptop. Today, Arduino gets its own screen — a 16×2 LCD display. That means 16 columns and 2 rows of text. Not big, but enough to show sensor readings, a menu, or a friendly greeting. And it doesn’t need a laptop — it works standalone.

What you need today

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• Arduino Uno + USB cable
• Breadboard
• 1 × 16×2 LCD display with I2C module on the back (the small board soldered to the back of the LCD — has 4 pins: GND, VCC, SDA, SCL)
• 4 female-to-male jumper wires

Why the I2C module?

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A bare 16×2 LCD (without the I2C add-on) needs 16 wires to connect. It’s a mess. The I2C module (the small green or blue board soldered to the back of the LCD) shrinks that down to just 4 wires — power, ground, and two signal wires. It uses a protocol called I2C (pronounced “eye-squared-C” or “eye-two-C”) to do all the communication.

Don’t worry about how I2C works under the hood. The library handles it. You just need to wire 4 pins correctly.

The circuit

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graph LR
    V5["5V"] --> VCC["LCD VCC"]
    GND["GND"] --> LG["LCD GND"]
    A4["Arduino A4"] --> SDA["LCD SDA"]
    A5["Arduino A5"] --> SCL["LCD SCL"]

Wiring:

1. LCD GND → Arduino GND
2. LCD VCC → Arduino 5V
3. LCD SDA → Arduino A4
4. LCD SCL → Arduino A5

The SDA and SCL pins are fixed on the Arduino Uno — they are physically pins A4 and A5. Even though they look like analog pins, when we use I2C they become data lines. (The Uno board may also have labeled “SDA” and “SCL” pins above the digital area — those are actually the same pins as A4/A5, just broken out to different spots on the board.)

Install the library

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We need a library called LiquidCrystal_I2C. It doesn’t come with the IDE by default — you have to install it.

1. Open the Arduino IDE.
2. Click Tools → Manage Libraries…
3. In the search box, type LiquidCrystal_I2C.
4. Find the one by Frank de Brabander (most common) or Marco Schwartz. Click Install.

Once it’s installed, you can use it in any sketch by #include-ing it at the top.

First code: Hello Anish!

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

// The 0x27 is the "address" of the LCD on the I2C bus.
// Most modules use 0x27 or 0x3F. If yours doesn't work, try 0x3F.
LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
  lcd.init();             // start the LCD
  lcd.backlight();        // turn on the backlight
  lcd.print("Hello Anish!");
}

void loop() {
  // Nothing — the text stays on the screen
}

Upload. The LCD backlight should come on (blue, usually), and “Hello Anish!” should appear on the top row.

If you see blocks or nothing: Try changing 0x27 to 0x3F in the line LiquidCrystal_I2C lcd(0x27, 16, 2); and upload again. That’s the second most common address.

If you see very faint text or nothing at all: There’s a tiny blue trimmer (a little screw) on the back of the I2C module. That’s the contrast adjustment. Turn it slowly with a small screwdriver until the text is clear.

What’s new in this code?

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

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Two libraries this time:

• Wire.h — the built-in Arduino library that handles I2C communication under the hood. The LCD library uses it, so we include it too.
• LiquidCrystal_I2C.h — the library we just installed. Gives us the LiquidCrystal_I2C object type.

Remember Day 12’s #include <Servo.h>? Same idea — pull in a library so you can use its commands.

LiquidCrystal_I2C lcd(0x27, 16, 2);

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This creates an LCD object called lcd. The three arguments configure it:

• 0x27 — the I2C address of this specific LCD module. Every I2C device has a unique address. 0x27 is the most common for these little LCDs.
• 16 — number of columns (character spaces per row).
• 2 — number of rows.

If you had a 20×4 LCD, you’d write LiquidCrystal_I2C lcd(0x27, 20, 4);. Same library, different size.

The 0x prefix means “hexadecimal” — a number system programmers use for low-level stuff. 0x27 equals 39 in regular decimal. You don’t need to understand hex right now. Just copy the number.

lcd.init();

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Initializes the LCD — wakes it up, clears it, tells it to start fresh. Call it once in setup().

lcd.backlight();

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Turns on the LCD’s backlight so you can actually see the text. There’s also lcd.noBacklight(); if you want to turn it off (useful for a dark mode or to save power).

lcd.print("Hello Anish!");

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Prints text at the current cursor position. Right after init(), the cursor is at column 0, row 0 (top-left). The text flows from left to right.

Notice how this looks exactly like Serial.print(...)? Same pattern — print text to a “thing.” The only difference is which thing we’re talking to (Serial for the laptop, lcd for the screen).

Position the cursor

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By default, lcd.print starts from wherever the cursor currently is. You can move the cursor with lcd.setCursor(col, row):

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void setup() {
  lcd.init();
  lcd.backlight();
  lcd.setCursor(0, 0);
  lcd.print("Hello Anish!");
  lcd.setCursor(0, 1);
  lcd.print("Day 15 rocks");
}

Note: columns and rows start at 0, not 1. Top-left is (0, 0), bottom-right on a 16×2 is (15, 1). Same zero-indexing habit as for loops and arrays.

Upload. Two lines of text, one on each row.

Blinking text

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Let’s make the text flash on and off.

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void setup() {
  lcd.init();
  lcd.backlight();
}

void loop() {
  lcd.setCursor(0, 0);
  lcd.print("Hello Anish!");
  delay(500);

  lcd.clear();         // wipe the screen
  delay(500);
}

Upload. The text shows for half a second, disappears, shows again, disappears. The new function is lcd.clear() — wipes the whole screen back to blank.

Common LCD commands

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Here are the main things you’ll use with the lcd object:

Just like the Serial library, you can print either text (in quotes) or a number (no quotes) or a variable.

Try this

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1. Print your name on the top row and “loves Arduino” on the bottom row.
2. Scrolling text. Use lcd.scrollDisplayLeft(); inside loop() with a delay to slide text across the screen. (Look it up in the library docs if you want a challenge.)
3. Count up. Create an int counter = 0; global, increment it in the loop, and print it on row 2 with a label: "Count: 42". Don’t forget lcd.clear() or setCursor() to overwrite the old number.
4. Show Day 9’s light sensor value on the LCD instead of in the Serial Monitor. Wire the LDR like before, read it, and print the value. (This is Day 16’s project, but you can start now.)

Don’t call lcd.clear() in a fast loop

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One warning: lcd.clear() is slow — it takes a few milliseconds. If you call it on every single loop iteration, your display will flicker badly. A better approach: only call clear() when something actually changes, or use lcd.setCursor() to overwrite the old text in place. We’ll do the overwriting trick tomorrow.

What you learned today

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• What a 16×2 LCD is and what the numbers mean
• Why the I2C module simplifies wiring (16 pins → 4 pins)
• How to install a library (Tools → Manage Libraries)
• #include <Wire.h> and #include <LiquidCrystal_I2C.h>
• Creating an LCD object: LiquidCrystal_I2C lcd(0x27, 16, 2);
• lcd.init(), lcd.backlight(), lcd.clear()
• lcd.setCursor(col, row) — position the cursor (0-indexed)
• lcd.print(...) — print text or numbers
• Why lcd.clear() in a fast loop causes flicker

What is next

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Day 16 — show real-time sensor data on the LCD. We’ll read the potentiometer and the LDR and display their values live, without flicker. Arduino gets its own dashboard.

Great work, Anish. Now the Arduino has a face.