In this tutorial we will build our own calculator with Arduino. The values can be sent in through a keypad (4×4 keypad) and result can be viewed on a LCD screen. This calculator could perform simple operations like Addition, Subtraction, Multiplication and Division with whole numbers. But once you understand the concept you can implement even scientific functions with Arduino’s built in functions.

Supplies

Arduino Uno

16×2 LCD Display

4×4 Keypad

Breadboard

Jumper Cables

Arduino Cable

Step 1: Schematics

Step 2: Installation of Library :

As told earlier we are going to interface a LCD and keypad with Arduino using libraries. So let’s add them to our Arduino IDE first. The library for LCD is already included in your Arduino by default so we need not worry about it. For Keypad library ( click on the link to download it from Github). You will get a ZIP file, then add this lib to Arduino by Sketch -> Include Library -> Add .ZIP file and point the location to this downloaded file. Once done we are all set for programming.

Step 3: Source Code :

/*
      © Techtronic Harsh
 
*/
#include <Keypad.h>
#include   <LiquidCrystal.h>
LiquidCrystal lcd(0, 1, 2, 3, 4, 5);
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] = {13,12,11,10};
byte colPins[COLS] = {9,8,7,6};
Keypad myKeypad = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );
boolean presentValue = false;
boolean next = false;
boolean final = false;
String num1, num2;
int answer;
char op;
void setup()
{
  lcd.begin(16,2);
  lcd.setCursor(0,0);
  lcd.print("Techtronic Harsh");
  lcd.setCursor(0,1);
  lcd.print("   Calculator");
  delay(3000);
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print("    Like And");
  lcd.setCursor(0,1);
  lcd.print("  Subscribe Us"    );
  delay(3000);
  lcd.clear();
}
void loop(){
  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 (presentValue != true)
    {
      num1 = num1 + key;
      int numLength = num1.length();
      lcd.setCursor(15 - numLength, 0); //to adjust one whitespace for operator
      lcd.print(num1);
    }
    else 
    {
      num2 = num2 + key;
      int numLength = num2.length();
      lcd.setCursor(15 - numLength, 1);
      lcd.print(num2);
      final = true;
    }
  }
  else if (presentValue == false && key != NO_KEY && (key == '/' || key == '*' || key == '-' || key == '+'))
  {
    if (presentValue == false)
    {
      presentValue = true;
      op = key;
      lcd.setCursor(15,0);
      lcd.print(op);
    }
  }
  else if (final == true && key != NO_KEY && key == '='){
    if (op == '+'){
      answer = num1.toInt() + num2.toInt();
    }
    else if (op == '-'){
      answer = num1.toInt() - num2.toInt();
    }
    else if (op == '*'){
      answer = num1.toInt() * num2.toInt();
    }
    else if (op == '/'){
      answer = num1.toInt() / num2.toInt();
    }    
      lcd.clear();
      lcd.setCursor(15,0);
      lcd.autoscroll();
      lcd.print(answer);
      lcd.noAutoscroll();
  }
  else if (key != NO_KEY && key == 'C'){
    lcd.clear();
    presentValue = false;
    final = false;
    num1 = "";
    num2 = "";
    answer = 0;
    op = ' ';
  }
}
/*
      © Techtronic Harsh
 
*/

Arduino_Calculator.ino
Download

Step 4: Working :

Make the connections as per circuit diagram and upload the code. If it shows error make sure you have added the library as per the instruction given above.

Character on Keypad and Assumption :