How to Make a Simple Arduino Uno Calculator

The Arduino is a software and hardware-based platform that makes the use of microcontrollers easy and is a source of learning the basics of circuit design for beginners. Moreover, this platform provides the opportunity for making small projects to very complex projects the easy way. A circuit for calculators is designed and is implemented using Arduino Uno in this discourse.

Making a Simple Arduino Uno Calculator

To make calculator using Arduino board there are some items required that are:

  • Arduino Uno
  • 4×4 membrane Keypad
  • Connecting wires
  • Breadboard
  • 16×2 LCD
  • Potentiometer
  • Breadboard

The schematic to follow to implement calculator using Arduino Uno is given below:

Hardware assembly for Simple Arduino Uno Calculator

We have implemented the circuit design on the hardware in such a way that first we have placed each component on the bread board except the Arduino Uno. Next we have  interfaced each component with Arduino using the connecting wires. There is an image posted below for better understanding the hardware implementation of this project.

Simple Arduino Uno Calculator Sketch

The Arduino code compiled for design a calculator using Arduino IDE is given as

#include <Keypad.h> // library for keypad
#include <LiquidCrystal.h>// library for LCD
LiquidCrystal lcd(A1, A0, 5, 4, 3, 2);// Arduino pins for LCD
const byte ROWS = 4; //initializing the rows of keypad
const byte COLS = 4;//initializing the columns of keypad

char keys [ROWS] [COLS] = { // giving values to each key of the keypad
  {'7', '8', '9', '/'},
  {'4', '5', '6', '*'},
  {'1', '2', '3', '-'},
  {'C', '0', '=', '+'}
byte rowPins[ROWS] = {13,12,11,10}; //Arduino pins for rows of keypad
byte colPins[COLS] = {9,8,7,6}; // Arduino pins for columns of keypad

Keypad myKeypad = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS ); /* function for mapping the values on the keys*/
// assigning boolean data type to the variables and initializing them with zero
boolean present = false; //
boolean next = false;
boolean final = false;
String num1, num2; // variables to display the keypad integer input
float ans;// for division operator the float data type is used for answer of the operation
char op;// assigning character data types to the arithmetic operators

void setup()
  lcd.begin(16,2); // initializing the LCD
  lcd.setCursor(3,0); // setting the place for displaying the first data line
  lcd.setCursor(3,1);//setting the place for displaying the second data line


void loop(){
// using the getkey function to get the value of the key pressed
  char key = myKeypad.getKey();

  if (key != NO_KEY && (key=='1'||key=='2'||key=='3'||key=='4'||key=='5'||key=='6'||key=='7'||key=='8'||key=='9'||key=='0'))
    if (present != true)
      num1 = num1 + key; // storing the value of key pressed in num1
      float numLength = num1.length();
      lcd.setCursor(0, 0); //to adjust one whitespace for operator
      lcd.print(num1); // printing the first number entered
      num2 = num2 + key;//storing the value of second key pressed in num2
      float numLength = num2.length();
      lcd.setCursor(2, 0);
      lcd.print(num2); //printing the second number entered
      final = true;
// condition for the if the key having arithmetic operator as its value is pressed
  else if (present == false && key != NO_KEY && (key == '/' || key == '*' || key == '-' || key == '+'))
    if (present == false)
      present = true;
      op = key; // saving the Arithmetic operator in the op variable
// conditions for working of the Arithmetic operators
  else if (final == true && key != NO_KEY && key == '='){
    if (op == '+'){
      ans = num1.toFloat() + num2.toFloat();

The Arduino code is compiled in such a way that first the libraries for keypad and LCD are defined. Then the size and key bindings of the keypad are declared, and the Arduino pins allotted to the LCD are also declared.

Similarly, the key bindings assigned to each key are mapped on the keypad using the mykeypad function. After that the variables having Boolean data type are declared for making the decisions in the code.

In the code there is one main if condition  for recognizing the key binding having the integer value and there is one main else if condition for recognizing the arithmetic operators.

In a nutshell if a key with integer value is pressed it is stored in the variable num1 and num2. Similarly, if the key binding has an arithmetic operator as its value, it will be stored in the character variable op and based on the operator selected a specific loop for that operator is executed and the result is displayed in the LCD.

Simulation and hardware demonstration of Simple Arduino Uno Calculator 

To give a clearer concept of creating a calculator using Arduino  we have given the output of hardware followed by the simulation we carried out in proteus software. The image posted below shows the simulation of the making calculator using Arduino Uno. 

The next image given is the demonstration of the working of the Arduino code compiled for the creating the calculator using Arduino Uno:


For making projects on the beginner as well as on the advanced level the Arduino family provides a variety of boards depending on the nature of the project. The platform provided by the Arduino can be effectively used for university and high school students to learn about circuits. A small project of making a calculator is made using the Arduino Uno board in this write-up. 

About the author

Aaliyan Javaid

I am an electrical engineer and a technical blogger. My keen interest in embedded systems has led me to write and share my knowledge about them.