Arduino Based Simple Calculator with 16×2 LCD and Keypad

Build a simple calculator using Arduino, 4×4 keypad, and 16×2 LCD display. Learn how to design, code, and expand this project from scratch with a complete guide and circuit diagram.

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🧠 Introduction

What is it?

This project is a DIY digital calculator built using an Arduino Uno, a 4×4 matrix keypad, and a 16×2 LCD display. It can perform basic arithmetic operations like addition, subtraction, multiplication, and division.

What the project does

When powered on, the calculator takes two operands and an operator as input from the keypad. It processes the inputs using Arduino logic and displays the result on the LCD.

Real-world use case

This kind of project is a gateway to embedded systems design. The integration of keypad interfacing, LCD display control, and core arithmetic logic replicates fundamental elements of many consumer electronic devices.

Skill level and expected outcome

✅ Level: Beginner to Intermediate
✅ Outcome: You’ll learn keypad scanning, LCD interfacing, and code optimization for logical operations using Arduino.

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📦 Components Required

Component	Quantity	Description	Buy Link
Arduino Uno R3	1	Main micro controller board	Buy from Elecsynergy
4×4 Matrix Keypad	1	Input device for entering digits and operations	Buy from Elecsynergy
16×2 LCD Display	1	Display the input and result	Buy from Elecsynergy
10K Potentiometer	1	Adjust LCD brightness	Buy from Elecsynergy
Breadboard	1	Circuit prototyping	Buy from Elecsynergy
Jumper Wires	~20	Electrical connections	Buy from Elecsynergy
USB Cable (A to B)	1	Arduino programming	Buy from Elecsynergy
9V Battery + DC Connector	1	Optional portable power	Buy from Elecsynergy

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🔌 Circuit Diagram + Explanation

Circuit Diagram

Key Connections:

• LCD (16×2):
  • RS → Pin 7
  • E → Pin 6
  • D4 → Pin 5
  • D5 → Pin 4
  • D6 → Pin 3
  • D7 → Pin 2
  • VSS → GND
  • VDD → +5V
  • V0 → Middle terminal of potentiometer
  • RW → GND
  • A, K (Backlight) → +5V and GND
• 4×4 Keypad:
  • Connect 8 pins to Digital Pins 8 to 13 and A0–A1

Explanation:

The keypad sends key presses to the Arduino. Based on these inputs, the Arduino processes operands and operators. The results are displayed on the LCD in real time.

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💻 Arduino Code

#include <LiquidCrystal.h>
#include <Keypad.h>

LiquidCrystal lcd(7, 6, 5, 4, 3, 2);

// Keypad setup
const byte ROWS = 4;
const byte COLS = 4;
char keys[ROWS][COLS] = {
  {'1','2','3','+'},
  {'4','5','6','-'},
  {'7','8','9','*'},
  {'C','0','=','/'}
};
byte rowPins[ROWS] = {8, 9, 10, 11};
byte colPins[COLS] = {12, 13, A0, A1};

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

String input = "";
char operation;
float firstNum, secondNum;

void setup() {
  lcd.begin(16,2);
  lcd.print("Calc Ready");
  delay(1000);
  lcd.clear();
}

void loop() {
  char key = keypad.getKey();

  if (key) {
    if (key >= '0' && key <= '9') {
      input += key;
      lcd.print(key);
    } else if (key == '+' || key == '-' || key == '*' || key == '/') {
      firstNum = input.toFloat();
      operation = key;
      input = "";
      lcd.setCursor(0,1);
      lcd.print(operation);
    } else if (key == '=') {
      secondNum = input.toFloat();
      float result = 0;

      switch (operation) {
        case '+': result = firstNum + secondNum; break;
        case '-': result = firstNum - secondNum; break;
        case '*': result = firstNum * secondNum; break;
        case '/': result = secondNum != 0 ? firstNum / secondNum : 0; break;
      }

      lcd.clear();
      lcd.setCursor(0,0);
      lcd.print("Result: ");
      lcd.print(result);
      delay(2000);
      lcd.clear();
      input = "";
    } else if (key == 'C') {
      input = "";
      lcd.clear();
    }
  }
}

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⚙️ Working Explanation

The Arduino receives numeric and operational inputs via the 4×4 matrix keypad. The logic stored in the micro controller performs arithmetic operations based on button inputs.

• Key Input: Captured as a string and converted to float.
• Operator Detection: Triggers the transition from first to second operand.
• Result Computation: Executes arithmetic logic and displays it on the LCD.

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🎥 Demo / Output Preview

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🛠️ Troubleshooting & Tips

Issue	Fix
LCD not showing anything	Check contrast potentiometer and wiring
Wrong result on operations	Ensure float conversion and operator switch logic are intact
Keypad not responsive	Recheck wiring and debounce delays
LCD flickers	Add delays and use lcd.clear() strategically

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🚀 Project Expansion Ideas

• Add decimal point support
• Use I2C LCD to reduce pin count
• Add EEPROM storage for previous result
• Integrate with a buzzer for sound feedback
• Make it a scientific calculator using menus

Challenge Yourself: Try adding a memory button (M+) or square root function!

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📚 Conclusion

This Arduino-based calculator project demonstrates a practical application of keypad scanning and LCD interfacing. It’s a stepping stone into more complex human-machine interfaces and digital electronics.

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🛒 Buy the Full Kit from Elecsynergy

Ready to build? Save time and order the complete kit directly from our store:

👉 Buy Calculator Project Kit – Elecsynergy