Build a Calculator with Arduino UNO
Tutorial plan
1- Objective of the project
2- Required Components
3- Circuit Connections of system
4- Program of Arduino calculator
Objective of the project
The objective of this project is to design and build an electronic calculator using the Arduino UNO board, a 4×4 matrix keypad, and an LCD I2C screen.
This calculator allows the user to enter numbers and select mathematical operations using the keypad, while the LCD screen displays the entered data and the calculation results in real time.
This project helps learners understand how to interface input devices (keypad) and output devices (LCD display) with a microcontroller. It also introduces fundamental programming concepts such as data input, processing, and output.
By completing this project, students will gain practical experience in electronics, embedded systems, and Arduino programming, and will learn how to create a functional and interactive embedded application.
Required Components
1. Arduino UNO
The Arduino UNO is the main controller of the system. It executes the program written in Arduino language, reads the keys pressed on the keypad, performs the mathematical calculations, and sends the results to the LCD screen. It also provides power and communication to the connected components.
2. 4x4 Matrix Keypad
The 4×4 matrix keypad is an input device that allows the user to enter numbers (0–9) and mathematical operators (+, −, ×, ÷, =, C). It consists of 16 buttons arranged in rows and columns. The Arduino scans these rows and columns to detect which key is pressed.
4. LCD Display with I2C Module
The LCD I2C display is used to show: entered numbers, mathematical operations and calculation results.
5. Breadboard
A breadboard can be used to make connections easier without soldering. It helps organize the circuit and allows quick modifications.
6. Jumper Wires
Jumper wires are used to connect the keypad and LCD screen to the Arduino board. They ensure proper electrical connections between all components.
Circuit Connections of system
1- Connection of keypad to Arduino UNO
| 4x4 Keypad | Arduino UNO |
|---|---|
| R1 | pin 2 |
| R2 | pin 3 |
| R3 | pin 4 |
| R4 | pin 5 |
| C1 | pin 6 |
| C2 | pin 7 |
| C3 | pin 8 |
| C4 | pin 9 |
2- Connection of LCD I2C display to Arduino UNO
| LCD I2C display | Arduino UNO |
|---|---|
| VCC | 5V |
| GND | GND |
| SDA | pin A4 |
| SCL | pin A5 |
Program of Arduino calculator
This program transforms the Arduino UNO into a functional calculator using a 4x4 matrix keypad for input and an I2C LCD display for output.
You need to install this libraries : LiquidCrystal_I2C and Keypad.
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#include <Wire.h> // Library for I2C communication #include <LiquidCrystal_I2C.h> // Library to control the I2C LCD display #include <Keypad.h> // Library to manage the matrix keypad // ---------------- LCD ---------------- // Create an LCD object with I2C address 0x27, 20 columns and 4 rows LiquidCrystal_I2C lcd(0x27, 20, 4); // ---------------- Keypad ---------------- // Define number of rows and columns of the keypad const byte ROWS = 4; const byte COLS = 4; // Define the characters of each key char keys[ROWS][COLS] = { {'1','2','3','+'}, {'4','5','6','-'}, {'7','8','9','*'}, {'C','0','=','/'} }; // Arduino pins connected to keypad rows byte rowPins[ROWS] = {9, 8, 7, 6}; // Arduino pins connected to keypad columns byte colPins[COLS] = {5, 4, 3, 2}; // Create keypad object Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS); // ---------------- Variables ---------------- // Variable to store the mathematical expression entered by the user String expression = ""; // ---------------- SETUP ---------------- void setup() { lcd.init(); // Initialize the LCD lcd.backlight(); // Turn on the LCD backlight lcd.clear(); // Clear the screen // Display startup message lcd.setCursor(0,0); lcd.print("Arduino Calculator"); delay(10000); // Wait for 10 seconds lcd.clear(); // Clear the screen } // ---------------- Calculation function ---------------- // This function evaluates the mathematical expression float calculer(String exp) { // Arrays to store numbers and operators float nombres[10]; char ops[10]; int nCount = 0; // Number counter int oCount = 0; // Operator counter // ---- Expression parsing ---- // Example: "12+3*4" // nombres = {12,3,4} // ops = {'+','*'} String temp = ""; for (int i = 0; i < exp.length(); i++) { char c = exp[i]; // If the character is a digit, add it to the temporary number if (isdigit(c)) { temp += c; } // If the character is an operator else { nombres[nCount++] = temp.toFloat(); // Store the number ops[oCount++] = c; // Store the operator temp = ""; // Reset temporary string } } // Store the last number nombres[nCount++] = temp.toFloat(); // ---- Handle multiplication and division first ---- // These operations have higher priority for (int i = 0; i < oCount; i++) { if (ops[i] == '*' || ops[i] == '/') { float res; if (ops[i] == '*') res = nombres[i] * nombres[i+1]; else res = nombres[i] / nombres[i+1]; // Replace the two numbers with the result nombres[i] = res; // Shift numbers to the left for (int j = i + 1; j < nCount - 1; j++) nombres[j] = nombres[j + 1]; // Shift operators to the left for (int j = i; j < oCount - 1; j++) ops[j] = ops[j + 1]; nCount--; oCount--; i--; } } // ---- Handle addition and subtraction ---- float resultat = nombres[0]; for (int i = 0; i < oCount; i++) { if (ops[i] == '+') resultat += nombres[i+1]; if (ops[i] == '-') resultat -= nombres[i+1]; } return resultat; // Return the final result } // ---------------- LOOP ---------------- void loop() { // Read the pressed key char touche = keypad.getKey(); // If a key is pressed if (touche) { // ---- Clear function ---- if (touche == 'C') { expression = ""; // Reset the expression lcd.clear(); // Clear the LCD } // ---- Calculate result ---- else if (touche == '=') { // Check if expression is not empty if (expression.length() > 0) { float res = calculer(expression); // Calculate result lcd.setCursor(0,2); lcd.print("= "); lcd.print(res); // Display result expression = ""; // Reset expression } } // ---- Add key to expression ---- else { expression += touche; // Add pressed key to expression lcd.setCursor(0,0); lcd.print(expression); // Display expression } } } |
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