For the “Arduino For Kooks” course, I recommend you get the Arduino Starter Kit available here.

As we’ve learned throughout this series, a microcontroller like the one on the Arduino is basically a rudimentary computer that can execute instruction sets very quickly because it doesn’t have to load all those pesky applications and operating systems. What better capstone for this basic course than to combine everything that we’ve learned so far and build our own rudimentary mathematical computation device: a simple calculator!

For this calculator, we’re going to use a basic 4×4 matrix keypad and attach it to the Arduino in such a way that we only need to use 8 pins to cover the functions of 16 individual switches!

The Circuit:

Connect the character LCD and potentiometer as we learned in the Liquid Crystal Ball project, using the Arduino pins shown in the diagram. You can use a breadboard to create busses for +5V and GND.

Connect the pins of the keypad to pins D0-D8 on the Arduino as shown.

The Sketch:


#include //Header file for LCD from https://www.arduino.cc/en/Reference/LiquidCrystal
#include //Header file for Keypad from https://github.com/Chris--A/Keypad

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.

Keypad kpd = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS ); // Create the Keypad

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 162 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 = (Number10) + 1; //Pressed twice
}

if (key == '4') //If Button 4 is pressed
{Serial.println ("Button 4");
if (Number==0)
Number=4;
else
Number = (Number10) + 4; //Pressed twice
}

if (key == '7') //If Button 7 is pressed
{Serial.println ("Button 7");
if (Number==0)
Number=7;
else
Number = (Number10) + 7; //Pressed twice
}

if (key == '0')
{Serial.println ("Button 0"); //Button 0 is Pressed
if (Number==0)
Number=0;
else
Number = (Number10) + 0; //Pressed twice
}

if (key == '2') //Button 2 is Pressed
{Serial.println ("Button 2");
if (Number==0)
Number=2;
else
Number = (Number10) + 2; //Pressed twice
}

if (key == '5')
{Serial.println ("Button 5");
if (Number==0)
Number=5;
else
Number = (Number10) + 5; //Pressed twice
}

if (key == '8')
{Serial.println ("Button 8");
if (Number==0)
Number=8;
else
Number = (Number10) + 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 = (Number10) + 3; //Pressed twice
}

if (key == '6')
{Serial.println ("Button 6");
if (Number==0)
Number=6;
else
Number = (Number10) + 6; //Pressed twice
}

if (key == '9')
{Serial.println ("Button 9");
if (Number==0)
Number=9;
else
Number = (Number10) + 9; //Pressed twice
}

if (key == 'A' || key == 'B' || key == 'C' || key == 'D') //Detecting Buttons on Column 4
{
Num1 = Number;
Number =0;
if (key == 'A')
{Serial.println ("Addition"); action = '+';}
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 = Num1Num2;

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
}

Congratulations!

If you have completed all 9 lessons in this course, then you have completed the Arduino for Kooks basic-level course! You have learned most of the wiring and programming rudiments necessary to go on and build your very own projects with the Arduino platform!

As a reward for your efforts, I have designed a “merit badge” that you can attach to your EDC, patch wall, or a sweet hacker jacket. You’ve worked hard to achieve it, so show off your new skill set!

CLICK HERE TO ORDER YOUR BADGE