## Introduction: Arduino Calculator

Programming is always fun and Arduino is a wonderful platform if you are just getting started with Embedded programming. 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 (16×2 Dot-matrix). 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.

At the end of this project you will know how to use a 16x2 LCD and Keypad with Arduino and also how easy it is to program for them using the readily available libraries. You will also understand how to program your Arduino for accomplishing a particular task.

## Step 1: Things Required

Arduino Uno (Any version will work)
16×2 LCD Display
9V Battery

## Step 3: Arduino Calculator Program

The complete Arduino program for this project is given at the end of this project. The code is split into small meaningful chunks and explained below.

Even though we have used a library for using a keypad we have to mention few details (shown below) about the keypad to the Arduino. The variable ROWS and COLS will tell how many rows and columns our keypad has and the keymap shows the order in which the keys are present on the keyboard. The keypad that i am using in this project looks like this below to the key map also represents the same.

Further below we have mentioned to which pins the Keypad is connected using the variable array rowPins and colPins.

const byte ROWS = 4; // Four rows
const byte COLS = 4; // Three columns

// Define the Keymap
char keys[ROWS][COLS] = {
{'1','2','3','A'},
{'4','5','6','B'},
{'7','8','9','C'},
{'*','0','#','D'}
};
byte rowPins[ROWS] = { 0, 1, 2, 3 };// Connect keypad ROW0, ROW1, ROW2 and ROW3 to these Arduino pins.
byte colPins[COLS] = { 4, 5, 6, 7 }; // Connect keypad COL0, COL1 and COL2 to these Arduino pins.

Once we have mentioned what type of keypad we are using and how it is connected, we can create the keypad using those details using the line below

Similarly we also have to tell to which pins of the Arduino the LCD is connected to. According to our circuit diagram the definitions would be like below

const int rs = 8, en = 9, d4 = 10, d5 = 11, d6 = 12, d7 = 13; //Pins to which LCD is connected
LiquidCrystal lcd(rs, en, d4, d5, d6, d7); //create the LCD

Inside the setup function, we just display the name of the project and then proceed to while loop where the main project lies.

Basically, we have to check if anything is being typed on the keypad, if typed we have to recognize what is being typed and then convert it to a variable when the “=” is pressed we have to calculate the result and then finally display it on the LCD. This is exactly what is done inside the loop function as shown below

key = kpd.getKey(); //storing pressed key value in a char

if (key!=NO_KEY)
DetectButtons();

if (result==true)
CalculateResult();

DisplayResult();

What happens inside each function is explained using the comment lines, go through the complete code below, fiddle around with it to understand how it actually works. If you have any doubt on a specific line, feel free to use the comment section or the forums.

## Step 5: Working of Arduino Calculator

Make the connections as per circuit diagram and upload the code below. If it shows error make sure you have added the library as per the instruction given above. You can also try the simulation to check if the problem is with your hardware. If everything is done as it’s supposed to be, then your hardware will look something like this below with the LCD displaying this

Arduino Calculator using 4x4 Keypad in action

Since the keypad used here does not have proper markings on it I have assumed the Alphabets to be operators as listed below

Assumed to be

“A”

“B”

Subtraction (-)

“C”

Multiplication (*)

“D”

Division (/)

“*”

Clear (C)

“#”

Equals (=)

You can use a marker to write over what each button actually represents.

With that done, you can directly start using the calculator. Types the number and will appear on the second line press the operand and type your second number finally press the “#” key to get your result. You can also try building this Touchscreen based Arduino calculator.

## Step 6: Code

/*
*/

#include //Header file for LCD from https://www.arduino.cc/en/Reference/LiquidCrystal

const byte ROWS = 4; // Four rows
const byte COLS = 4; // Three columns

// Define the Keymap
char keys[ROWS][COLS] = {

{'7','8','9','D'},

{'4','5','6','C'},

{'1','2','3','B'},

{'*','0','#','A'}

};

byte rowPins[ROWS] = { 0, 1, 2, 3 };// Connect keypad ROW0, ROW1, ROW2 and ROW3 to these Arduino pins.
byte colPins[COLS] = { 4, 5, 6, 7 }; // Connect keypad COL0, COL1 and COL2 to these Arduino pins.

const int rs = 8, en = 9, d4 = 10, d5 = 11, d6 = 12, d7 = 13; //Pins to which LCD is connected
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

long Num1,Num2,Number;
char key,action;
boolean result = false;

void setup() {
lcd.begin(16, 2); //We are using a 16*2 LCD display
lcd.print("DIY Calculator"); //Display a intro message
lcd.setCursor(0, 1); // set the cursor to column 0, line 1
lcd.print("-CircuitDigest"); //Display a intro message

delay(2000); //Wait for display to show info
lcd.clear(); //Then clean it
}

void loop() {

key = kpd.getKey(); //storing pressed key value in a char

if (key!=NO_KEY)
DetectButtons();

if (result==true)
CalculateResult();

DisplayResult();
}

void DetectButtons()
{
lcd.clear(); //Then clean it
if (key=='*') //If cancel Button is pressed
{Serial.println ("Button Cancel"); Number=Num1=Num2=0; result=false;}

if (key == '1') //If Button 1 is pressed
{Serial.println ("Button 1");
if (Number==0)
Number=1;
else
Number = (Number*10) + 1; //Pressed twice
}

if (key == '4') //If Button 4 is pressed
{Serial.println ("Button 4");
if (Number==0)
Number=4;
else
Number = (Number*10) + 4; //Pressed twice
}

if (key == '7') //If Button 7 is pressed
{Serial.println ("Button 7");
if (Number==0)
Number=7;
else
Number = (Number*10) + 7; //Pressed twice
}

if (key == '0')
{Serial.println ("Button 0"); //Button 0 is Pressed
if (Number==0)
Number=0;
else
Number = (Number*10) + 0; //Pressed twice
}

if (key == '2') //Button 2 is Pressed
{Serial.println ("Button 2");
if (Number==0)
Number=2;
else
Number = (Number*10) + 2; //Pressed twice
}

if (key == '5')
{Serial.println ("Button 5");
if (Number==0)
Number=5;
else
Number = (Number*10) + 5; //Pressed twice
}

if (key == '8')
{Serial.println ("Button 8");
if (Number==0)
Number=8;
else
Number = (Number*10) + 8; //Pressed twice
}

if (key == '#')
{Serial.println ("Button Equal");
Num2=Number;
result = true;
}

if (key == '3')
{Serial.println ("Button 3");
if (Number==0)
Number=3;
else
Number = (Number*10) + 3; //Pressed twice
}

if (key == '6')
{Serial.println ("Button 6");
if (Number==0)
Number=6;
else
Number = (Number*10) + 6; //Pressed twice
}

if (key == '9')
{Serial.println ("Button 9");
if (Number==0)
Number=9;
else
Number = (Number*10) + 9; //Pressed twice
}

if (key == 'A' || key == 'B' || key == 'C' || key == 'D') //Detecting Buttons on Column 4
{
Num1 = Number;
Number =0;
if (key == 'A')
if (key == 'B')
{Serial.println ("Subtraction"); action = '-'; }
if (key == 'C')
{Serial.println ("Multiplication"); action = '*';}
if (key == 'D')
{Serial.println ("Devesion"); action = '/';}

delay(100);
}

}

void CalculateResult()
{
if (action=='+')
Number = Num1+Num2;

if (action=='-')
Number = Num1-Num2;

if (action=='*')
Number = Num1*Num2;

if (action=='/')
Number = Num1/Num2;
}

void DisplayResult()
{
lcd.setCursor(0, 0); // set the cursor to column 0, line 1
lcd.print(Num1); lcd.print(action); lcd.print(Num2);

if (result==true)
{lcd.print(" ="); lcd.print(Number);} //Display the result

lcd.setCursor(0, 1); // set the cursor to column 0, line 1
lcd.print(Number); //Display the result
}

Participated in the
Arduino Contest 2019