Arduino Calculator Using 4X4 Keypad

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.

/*
      © 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
 
*/

Attachments

• Arduino_Calculator.ino
  Download

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 :

• “A” - Addition (+)
• “B” - Subtraction (-)
• “C” - Multiplication (*)
• “D” - Division (/)
• “*” - Clear (C)
• “#” - Equals (=)