A DIY Calculator Using PIC16F876A

I decide to make a simple digital calculator with my own components, seven-segment display. PIC16F876A, and push button, etc. However it's not useful in current application because a calculator presents in many electronics device such as a smart phone, tablet, and personal computer, etc.

A DIY Calculator Using PIC16F876A 

This calculator is able to handle up to 8 digits, including a negative sign. It can perform arithmetic addition, subtraction, multiplication, and division. The data type is only signed integer number. 

I use MikroC Pro for PIC to program this typical 8-bit controller. The total lines of code is quite high.

 
 
#define GA (1<<3)
char keypadPort at PORTB;
char key_char[16]= {7,8,9,15,4,5,6,14,1,2,3,13,10,0,11,12};
char send_key,dig[8];
unsigned char cnt;
 
void interrupt(void){
    if(INTCON.TMR0IF)
    cnt++;
    INTCON.TMR0IF=0;
    }
 
void system_init();
void ssd_out();
 
void main() {
     char key=0,old_key=0;
     char i=0,j=0;
     char CntKey=0;
     system_init();
     while(1){
       key=Keypad_Key_Click();
       if(key!=0&&CntKey<8){
                  send_key=key-1;
                  /*dig[5]=dig[4];
                  dig[4]=dig[3];
                  dig[3]=dig[2];
                  dig[2]=dig[1];
                  dig[1]=dig[0];*/
                  for(i=7;i>0;i--) dig[i]=dig[i-1];
                  dig[0]=key_char[send_key];
                  CntKey++;
                  }
 
       ssd_out();
      }
}
 
void system_init(){
     TRISC=0x00;
     TRISA=0x00;
     PORTA=0x00;
     PORTC=0x00;
     ADCON1=0x07;
     OPTION_REG=0x85;
     INTCON.GIE=1;
     INTCON.TMR0IE=1;
     INTCON.TMR0IF=0;
     Keypad_Init();
     cnt=0;
     send_key=0;
}
 
void ssd_out(){
const char sg[16]={0x3F,0x06,0x5B,0x4F,0x66,0x6D,0x7D,
0x07,0x7F,0x6F,0x77,0x7C,0x39,0x5E,0x79,0x71} ;
// const char dg[6]={0x20,0x10,0x08,0x04,0x02,0x01};
     switch(cnt){
                 case 1:
                      PORTA=0x00;
                      PORTC=sg[dig[7]];
                      PORTA=0x00|GA;
                      break;
 
                 case 2:
                      PORTA=0x00;
                      PORTC=sg[dig[6]];
                      PORTA=0x01|GA;
                      break;
 
                 case 3:
                      PORTA=0x00;
                      PORTC=sg[dig[5]];
                      PORTA=0x02|GA;
                      break;
 
                 case 4:
                      PORTA=0x00;
                      PORTC=sg[dig[4]];
                      PORTA=0x03|GA;
                      break;
 
                 case 5:
                      PORTA=0x00;
                      PORTC=sg[dig[3]];
                      PORTA=0x04|GA;
                      break;
 
                 case 6:
                      PORTA=0x00;
                      PORTC=sg[dig[2]];
                      PORTA=0x05|GA;
                      break;
 
                 case 7:
                      PORTA=0x00;
                      PORTC=sg[dig[1]];
                      PORTA=0x06|GA;
                      break;
 
                 case 8:
                      PORTA=0x00;
                      PORTC=sg[dig[0]];
                      PORTA=0x07|GA;
                      break;
 
                 case 9:
                      cnt=1;
                      PORTA=0x00;
                      break;
                 }
 
}

I use keypad library of this compiler to scan its 4x4 matrix keypad.

Schematic Diagram

The PCB is assumed to be a single side layer. It's easy to fabricate at home.

Bottom Layer copper normal no mirror

Top silk normal no mirror

A sample 3D design

Top side

Bottom side

Click here to download its source file.