Basic Standard Calculator(Using ATMega16 Microcontroller)

Aim of this project is to design a calculating device capable of performing basic calculations (add, subtract, multiply, divide) on two operands.

Project overview

Basic Standard Calculator

Hardware components required

1. ATMega 16 microcontroller2. Basic calculator keypad3. 2x16 LCD

Keypad and LCD are connected with microcontroller to make an easy man-machine interface to make the calculator capable of performing the desired function.

ATMega16 microcontroller : This is the brain of system which is programmed to take input from user through keypad, perform the desired operation and then display the result on the provided 2x16 LCD.

Basic calculator keypad : This is a 4x4 (having 4 rows and 4 columns) keypad which is interfaced with microcontroller with its each key assigned a specific no. or operator defined in the program.

2x16 LCD : this is the liquid crystal display module capable of displaying 32 characters in two rows (16 in each row). Microcontroller displays characters on it while taking inputs from user and to display the result to user.

Interfacing keypad with microcontroller

Keyboard Connections to PORTS

With matrix keypads 16 keys can function with 8 pins (4 rows and 4 columns) of microcontroller’s either same or different ports as convenient.

Scanning and identifying the key pressed

Function to identify a key pressed

//connect colum with lower nibble and rows with upper nibble

#define key_port PORTA

#define key_ddr DDRA

#define key_pin PINA

unsigned char keypad[4][4]={'7','8','9','/',

'4','5','6','*',

'1','2','3','-',

'c','0','=','+'};

char takekey()

{

unsigned char row,colum;

char key;

key_ddr=0xf0;

key_port=0xff;

do

{

key_port&=0x0f;

colum=(key_pin&0x0f);

}while(colum!=0x0f);

do

{

do

{

_delay_ms(1);

key_port&=0x0f;

colum=(key_pin&0x0f);

}while(colum==0x0f);

_delay_ms(1);

key_port&=0x0f;

colum=(key_pin&0x0f);

}while(colum==0x0f);

while(1)

{

key_port=0xef;

colum=(key_pin&0x0f);

if(colum!=0x0f)

{

row=0;

break;

}

key_port=0xdf;

colum=(key_pin&0x0f);

if(colum!=0x0f)

{

row=1;

break;

}

key_port=0xbf;

colum=(key_pin&0x0f);

if(colum!=0x0f)

{

row=2;

break;

}

key_port=0x7f;

colum=(key_pin&0x0f);

row=3;

break;

}

if(colum==0x0e)

key=keypad[row][0];

else if(colum==0x0d)

key=keypad[row][1];

else if(colum==0x0b)

key=keypad[row][2];

else

key=keypad[row][3];

return(key);

}

Interfacing 2x16 LCD with microcontroller (in 4 bit mode)

LCD interfacing with atmega 16

LCD functions in accordance with above figure:#define en PA2 // enable signal

#define rw PA1 // read/write signal

#define rs PA0 // register select signal

void lcd_cmd(unsigned char cmd)

{

DDRA=0xff;

PORTA=0;

PORTA=cmd&0xf0;

lcd &=~(1<<rs);

lcd &=~(1<<rw);

lcd |= (1<<en);

_delay_ms(1);

lcd &=~(1<<en);

_delay_ms(1);

PORTA=((cmd<<4)&0xf0);

lcd &=~(1<<rs);

lcd &=~(1<<rw);

lcd |= (1<<en);

_delay_ms(1);

lcd &=~(1<<en);

_delay_ms(1);

return;

}

void lcd_data(unsigned char data)

{

PORTA=(data&0xf0);

lcd |=(1<<rs);

lcd &=~(1<<rw);

lcd |= (1<<en);

_delay_ms(1);

lcd &=~(1<<en);

_delay_ms(1); // delay to get things executed

PORTA= ((data<<4)&0xf0);

lcd |=(1<<rs);

lcd &=~(1<<rw);

lcd |= (1<<en);

_delay_ms(1);

lcd &=~(1<<en);

return ;

}

void ini_lcd(void)

{

_delay_ms(5);

lcd_cmd(0x02);

_delay_ms(1);

lcd_cmd(0x28);

_delay_ms(1);

lcd_cmd(0x01); // clear LCD

_delay_ms(1);

lcd_cmd(0x0E); // cursor ON

_delay_ms(1);

lcd_cmd(0x84);

_delay_ms(1);

return;

}

Calculator

The functioning of calculator s as follows:

i. Enter first operandii. Enter operator

iii. Enter second operandiv. Press result key

Main program:

#include<avr/io.h>

#include<util/delay.h>

#include"4bitlcd.h"

#include"keypad.h"

#define key_port PORTA

#define key_ddr DDRA

#define key_pin PINA

void lcd_cmd(unsigned char cmd);

void lcd_data(unsigned char data);

void ini_lcd(void);

void main()

{

unsigned char ch=0,op=0;

long o1=0,o2=0,o3=0,ch1=0;

PORTB=0XFF;

DDRB=0xff;

_delay_ms(5);

ini_lcd();

while(1)

{

lcd_data('k');

lcd_cmd(0x01);

_delay_ms(20);

ch=0;

op=0;

ch1=0;

o1=0;

o2=0;

o3=0;

lcd_cmd(0x80);

while((ch!='+')&(ch!='-')&(ch!='*')&(ch!='/')) //get first operand and operator

{

ch=takekey();

ch1=ch;

if((ch!='c')&(ch!='=')&(ch!='+')&(ch!='-')&(ch!='*')&(ch!='/'))

{

lcd_data(ch);

o1=((o1*10)+(ch1-0x30));

}

else

{

op=ch;

lcd_data(ch);

break;

}

}

ch=0;

ch1=0;

lcd_cmd(0xc0);

while((ch!='+')&(ch!='-')&(ch!='*')&(ch!='/')) //get second operand

{

ch=takekey();

ch1=ch;

if((ch!='c')&(ch!='=')&(ch!='+')&(ch!='-')&(ch!='*')&(ch!='/'))

{

lcd_data(ch);

o2=((o2*10)+(ch1-0x30));

}

else

{

lcd_cmd(0x01);

break;

}

}

switch(op) //apply operation

{

case '+':

o3=o1+o2;

lcd_data('a');

_delay_ms(5);

break;

case '-':

o3=o1-o2;

lcd_data('s');

_delay_ms(5);

break;

case '*':

o3=o1*o2;

lcd_data('m');

_delay_ms(5);

break;

case '/':

o3=o1/o2;

lcd_data('d');

_delay_ms(5);

break;

default:

lcd_cmd(0x01);

_delay_ms(5);

}

lcd_cmd(0xc2);

lcd_cmd(0x01);

lcd_cmd(0xce);

while(o3) //print result

{

lcd_data((o3%10)+0x30);

lcd_cmd(0x10);

lcd_cmd(0x10);

o3=o3/10;

}

ch=takekey();

lcd_cmd(0x01);

_delay_ms(5);

}

return ;

}