🧮 Arduino Calculator — 4×4 Keypad + 16×2 LCD

A fully functional hardware calculator built on Arduino Uno

Demo · Getting Started · Author

---

A fully functional hardware calculator built on Arduino Uno using a 4×4 matrix keypad for input and a 16×2 LCD for real-time expression display and result output.

---

📖 Table of Contents

• Demo
• Features
• Hardware
• Pin Connections
• Keypad Layout
• Software
• How to Run
• Project Structure
• Author

---

🖼️ Demo

Idle / Ready	Expression Input	Result Display

---

✨ Features

• Real-time expression display — shows full operand operator operand expression on LCD row 1
• Arithmetic operations — Addition (+), Subtraction (-), Multiplication (*), Division (/)
• Result on row 2 — displays = result instantly on = press
• Error handling — Division by zero and numeric overflow detected with descriptive LCD messages
• Clear All (C) — resets state with a "Cleared!" confirmation message
• Splash screen — animated "Divyanshu's Calculator" intro on power-up
• Blinking cursor — real-time cursor feedback using millis()-based non-blocking toggle
• Result chaining — result of one calculation can be directly used as input for the next
• 16-char display truncation — long expressions scroll from the left without crashing

---

🛠️ Hardware

Component	Specification
Microcontroller	Arduino Uno (ATmega328P)
Keypad	4×4 Matrix Keypad
Display	16×2 LCD (parallel interface)
Resistor	220Ω (LCD backlight current limiting)

---

🔌 Pin Connections

LCD → Arduino

LCD Pin	Arduino Pin
RS	D12
E	D11
D4	D10
D5	D9
D6	D8
D7	D7
VSS, RW, K	GND
VDD, A	5V (via 220Ω for backlight)

Keypad → Arduino

Keypad	Arduino
Row 1–4	D5, D4, D3, D2
Col 1–4	A3, A2, A1, A0

---

⌨️ Keypad Layout

[ 1 ] [ 2 ] [ 3 ] [ + ]
[ 4 ] [ 5 ] [ 6 ] [ - ]
[ 7 ] [ 8 ] [ 9 ] [ * ]
[ C ] [ 0 ] [ = ] [ / ]

---

💻 Software

Libraries Used

Library	Purpose
LiquidCrystal.h	LCD control (built-in Arduino)
Keypad.h	4×4 matrix keypad scanning

Install Keypad library via Arduino IDE: Tools → Manage Libraries → search "Keypad" by Mark Stanley

Key Implementation Details

• Matrix scanning — keypad rows driven via digital pins, columns read via analog pins configured as digital inputs
• Expression parser — memory stores left operand, current stores right operand; operation stores pending operator as char
• Non-blocking cursor blink — millis() / 400 % 2 toggles lcd.cursor() / lcd.noCursor() without delay()
• Float formatting — integer results displayed without decimal; float results shown to 3 decimal places
• Input limit — max 9 digits per operand to prevent buffer overflow

---

🚀 How to Run

1. Clone this repository:

   git clone https://github.com/Divyanshukumar2005/Arduino-Calculator.git

2. Open calculator.ino in Arduino IDE
3. Install the Keypad library (see above)
4. Connect hardware as per pin table
5. Upload to Arduino Uno — done!

---

📁 Project Structure

Arduino-Calculator/
├── calculator.ino       # Main source code
├── README.md            # This file
└── screenshots/         # Demo images
    ├── ready.png
    ├── input.png
    └── result.png

---

👨‍💻 Author

Divyanshu Kumar

B.Tech (Electronics & Communication Engineering) · University of Delhi

---

⭐ If you found this project useful or interesting, consider giving it a star!