🧮 Arduino Numpad Calculator

This project demonstrates how to build a fully functional calculator using an Arduino Uno, a 4x4 Matrix Keypad, and a 16x2 LCD Display.
It performs basic arithmetic operations — Addition, Subtraction, Multiplication, and Division — using physical button inputs.

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📦 Components Required

Component	Quantity	Description
Arduino Uno	1	Main microcontroller
4x4 Matrix Keypad	1	For number and operation input
16x2 LCD Display	1	To show input and results
Jumper Wires	~15	For connections
Breadboard	1	Optional, for easier wiring
USB Cable	1	For uploading code

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⚙️ Step 1: Circuit Wiring

Follow the diagram below for connecting all components correctly.

🖼️ Wiring Diagram:

🔌 Connections

Keypad → Arduino

Keypad Pin	Arduino Pin	Description
Row 1	D9	Input Row
Row 2	D8	Input Row
Row 3	D7	Input Row
Row 4	D6	Input Row
Col 1	D5	Input Column
Col 2	D4	Input Column
Col 3	D3	Input Column
Col 4	D2	Input Column

LCD → Arduino (Parallel Connection)

LCD Pin	Arduino Pin	Description
RS	D12	Register Select
E	D11	Enable
D4	D10	Data 4
D5	D9	Data 5
D6	D8	Data 6
D7	D7	Data 7
VSS	GND	Ground
VDD	5V	Power
RW	GND	Write Mode
V0	Potentiometer	Adjust LCD Contrast

💡 If using an I2C LCD, connect SDA → A4 and SCL → A5, and remove the individual data pins.

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💾 Step 2: Install Libraries

Before uploading the code, install the required Arduino libraries.

1. Keypad Library

   • Go to: Sketch → Include Library → Manage Libraries...
   • Search for Keypad by Mark Stanley & Alexander Brevig
   • Click Install

2. LiquidCrystal Library

   • Pre-installed with the Arduino IDE.

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💻 Step 3: Upload the Code

Copy and paste the following code into your Arduino IDE:

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