How to build a calculator using Pic16f877 microcontroller

Calculator with Pic 16f877 microcontroller is a comprehensive project. Comprehensive in the way that code is lengthy and logical. It will be hard for newbies to understand the code and circuit components interface with pic microcontroller. I will try to explain each and every thing about code and circuit thoroughly. The project covers all the aspects of programming and interfacing of 16×2 character lcd and 4×4 numeric keypad and pic16f877 microcontroller. One should already know about 16×2 lcd working and 4×4 numeric keypad interface with microcontroller before beginning with the project. I have a good tutorial on 16×2 lcd pin out and working. You must first go with this tutorial if you don’t know about 16×2 lcd pin out, working principle and interface with microcontrollers.

16×2 lcd Pin out and Working

What pic microcontroller calculator offers?

I am going to build a 2-Digit calculator with pic microcontroller. Four functions addition, subtraction, multiplication and division(+,-,/,*) can be performed on single digit numbers using the calculator made with pic microcontroller. User Inputs the numbers and operator using 4×4 numeric keypad and pic microcontroller after manipulating the numbers displays result on 16×2 lcd.

Calculator with pic microcontroller – Working

Calculator with pic microcontroller – Working

When you turn on/power the system. A message will be displayed on the 16×2 lcd first row “Enter First No = “. You enter the number. As soon as you enter number it will be displayed on the 16×2 lcd screen. Then a second message will appear on 16×2 lcd first row asking to “Enter Operator = “. You entered the operator. Then a third message will prompt up saying “Enter Second No= “. You entered the second number. When you are done with entering the second number. Result will be displayed on 16×2 lcd. Calculator arithmetic operation result is shown below.

Pic16f877 microcontroller calculator – Project requirements

  • Pic16f877 Microcontroller
  • 16×2 lcd 
  • 4×4 keypad
  • Crystal 20 MHz
  • Potentiometer/variable resistor (For setting Lcd Contrast)
  • Bread board or PCB for Circuit Designing
  • Power Supply

Two digit calculator with pic microcontroller – Circuit diagram

Lcd data pins are connected to Port-B of PIC16f877 Microcontroller. Lcd Controlling pins RS(Register Select) and EN(Enable) are connected to Port-D Pin# 6 & 7. Keypad is interfaced with Port-C of pic microcontroller. Rows of keypad are connected to lower nibble of Port-C. Coulombs are connected to upper nibble of Port-C. Apply 5 volts at VDD & VCC Pins of microcontroller and 16×2 lcd display. Ground VSS Pins of pic microcontroller and lcd display. Crystal is connected to Pin# 13 & 14 of PIC16f877 microcontroller. Circuit diagram of pic microcontroller calculator project is given below.

How to build a calculator using Pic16f877 microcontroller

Calculator using pic microcontroller – Project code

Code portion is little bit difficult. But if you are familiar with syntax of C++ language and did some good work in c++ then the code below is easy for you to understand and to modify. First htc.h header file is included in the project. This header file must be included in every project that is using HIGH-TECH C compiler for compiling the code. Since i am using HIGH-TECH C compiler so i included it. Then the statement _XTAL_FREQ 20e6 is defining our crystal frequency. Which is 20 MHz. Next i defined Port-C & D pins for 16×2 lcd and keypad interface. Each port pin is also given a meaning full name. After that some functions are defined. Then some strings are defined. These strings are displayed on 16×2 lcd display. The strings are used to communicate with the user.

Functions which are part of pic microcontroller calculator code

void main()
Main Function the heart of the code. Main function executes first. All other functions executes after it.
void lcdcmd  (unsigned char)
This function sends commands and controls lcds registers to execute the command properly.  
void lcddata (unsigned char)
This function sends data to lcd display and controls lcds registers to display data on 16×2 lcd.
void disp_num(float num)
This function displays calculated value or output result on 16×2 lcd display efficiently. 
int get_num  (char ch)
This function converts character value to integer. To display integer value on 16×2 lcd it must first be converted in to character format. On 16×2 lcd we can display a character 8-bit value.
void lcdinit ()
This function initializes the character lcd display. 16×2 lcd, font-size 7×5, cursor blinking etc.
char scan_key(void)
This functions checks which keypad key is pressed by the user.

Each and every Statement of the code is well commented. Go through the code and if you feel any problem in any statement just leave your queries in the comments section below.

 #define _XTAL_FREQ 20e6
 #define rs RD6
 #define en RD7
 #define r0 RC0
 #define r1 RC1
 #define r2 RC2
 #define r3 RC3
 #define c0 RC4
 #define c1 RC5
 #define c2 RC6
 #define c3 RC7
 void lcdcmd (unsigned char);
 void lcddata (unsigned char);
 void disp_num(float num);
 int get_num (char ch);
 void lcdinit ();
 char scan_key(void);
 unsigned char s[]={ENTER 1 NO= };
 unsigned char s1[]={ENTER 2 NO= };
 unsigned char s2[]={OPERATOR = };
 unsigned char s3[]={***RESULT***};
 void lcdinit(){
 __delay_ms(400); lcdcmd(0x30); __delay_ms(400); lcdcmd(0x30);
 __delay_ms(400); lcdcmd(0x30); __delay_ms(400); lcdcmd(0x38);
 lcdcmd(0x0F); lcdcmd(0x01); lcdcmd(0x06); lcdcmd(0x80);
 void main (void)
 TRISC=0xF0; //Rows Output, Coulombs Input
 TRISB=0x00; //Port-B as Output
 TRISD6=; //Port-D PIN-6 as Output
 TRISD7=; //Port-D PIN-7 as Output
 unsigned int count=;
 int k2,k1;
 char ke,key,key1;
 lcdinit(); //Initializing Lcd
 while(s[count]!=\0) //Displaying String s on LCD
 ke=scan_key(); //Scan the First Digit
 k2=get_num(ke); //Converting Char into number
 lcdcmd(0x01); //Clear Lcd
 while(s2[count]!=\0) //Displaying String s2 on LCD
 key=scan_key(); //Scaning operator
 lcdcmd(0x01); //Cleat Lcd
 while(s1[count]!=\0) //Displaying String s1 on LCD
 key1=scan_key(); //Scan Second digit
 k1=get_num(key1); //Converting Char into number
 lcdcmd(0x01); //Clear Lcd
 lcdcmd(0x82); //Start displying data on lcd at position Row=1 Coulomb=3
 while(s3[count]!=\0) //Displaying String s3 on LCD
 lcdcmd(0xC0); //Jump to second Line of Lcd
 lcddata( );
 case +:
 case :
 case *:
 case /:
 void lcdcmd(unsigned char value) //Sending Commands to Lcd
 PORTB = value;
 rs = ;
 en = 1;
 en = ;
 void lcddata(unsigned char value) //Sending Data to Lcd
 PORTB = value;
 rs = 1;
 en = 1;
 en = ;
 char scan_key() //Scan the Pressed Key by user
 unsigned char c=s;
 if(c0==1 && r0==){ lcddata(7);__delay_ms(500);return 7;c=a;}
 if(c1==1 && r0==){ lcddata(8);__delay_ms(500);return 8;c=a;}
 if(c2==1 && r0==){ lcddata(9);__delay_ms(500);return 9;c=a;}
 if(c3==1 && r0==){ lcddata(/);__delay_ms(500);return /;c=a;}
 if(c0==1 && r1==){ lcddata(4);__delay_ms(500);return 4;c=a;}
 if(c1==1 && r1==){ lcddata(5);__delay_ms(500);return 5;c=a;}
 if(c2==1 && r1==){ lcddata(6);__delay_ms(500);return 6;c=a;}
 if(c3==1 && r1==){ lcddata(*);__delay_ms(500);return *;c=a;}
 if(c0==1 && r2==){ lcddata(1);__delay_ms(500);return 1;c=a;}
 if(c1==1 && r2==){ lcddata(2);__delay_ms(500);return 2;c=a;}
 if(c2==1 && r2==){ lcddata(3);__delay_ms(500);return 3;c=a;}
 if(c3==1 && r2==){ lcddata();__delay_ms(500);return ;c=a;}
 if(c1==1 && r3==){ lcddata();__delay_ms(500);return ;c=a;}
 if(c3==1 && r3==){ lcddata(+);__delay_ms(500);return +;c=a;}
 return ;
 int get_num(char ch) //converting character into integer
 case : return ; break;
 case 1: return 1; break;
 case 2: return 2; break;
 case 3: return 3; break;
 case 4: return 4; break;
 case 5: return 5; break;
 case 6: return 6; break;
 case 7: return 7; break;
 case 8: return 8; break;
 case 9: return 9; break;
 return ;
 void disp_num(float num) //Displays calculated value on LCD
 unsigned char UnitDigit = ; //Contains unit digit of calculated value
 unsigned char TenthDigit = ; //contains 10th digit of calculated value
 unsigned char decimal = ;
 int j,numb;
 numb = –1*numb; // Make number positive
 lcddata(); // Display a negative sign on LCD
 TenthDigit = (numb/10); // Findout Tenth Digit
 if( TenthDigit != ) // If it is zero, then don’t display
 lcddata(TenthDigit+0x30); // Make Char of TenthDigit and then display it on LCD
 UnitDigit = numb – (TenthDigit*10);
 lcddata(UnitDigit+0x30); // Make Char of UnitDigit and then display it on LCD
 decimal=(j%10)+0x30; //Display If any value after Decimal Point
More projects about calculators involving different other microcontrollers. Each project is made with 16×2 lcd display, 4×4 keypad and an intelligent unit, the microcontroller. Every project is open source. One can modify and use code according to his/her needs.  
Download the project files, code(C, Hex) and simulation. Code is written is C Language using MP-LAB IDE and High-tech C compiler is used to compile the code. Simulation is made in Proteaus 8.0. Watch Project Video Below. Plz Give us your feed back on the project.

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