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.

ATMega16 two-digit multiplexing display and counting example

Display multiplexing is very common for most microcontroller programming and interfacing. In usual, a controller could drive up to 8 digits before we can see its display flickering. In this programming example, I use only two digits of 7-Segment display. Because it's easy to build the circuit with a  little of source codes.

Program simulation in Proteus

Controller keeps track of counting an external pulse generated by SW1 switch pressing. The maximum press counting is 60 before it rolls down to 0. The display will become flicker whenever the input switch has a longer press duration, but it's not longer than 250ms.

/*
 * mux2Ssd.c
 *
 * Created: 5/25/2022 7:20:40 PM
 * Author : Admin
 */ 
 
#include <avr/io.h>
 
#define F_CPU 4000000UL
#include <util/delay.h>
 
int main(void)
{
    //common cathode
    unsigned char SSD[10]={0x3F,0x06,0x5B,0x4F,0x66,0x6D,0x7D,0x07,0x7F,0x6F};
	unsigned char cnt=0;
	//PortC output
	DDRC=0xFF;
	//PD7 input
	DDRD&=~(1<<7);	
	//Turn on PD7
	PORTD|=(1<<7);
    while (1) 
    {
		//Display processing
		PORTD&=~(1<<0);
		PORTD&=~(1<<1);
		PORTC=SSD[cnt/10];
		PORTD|=(1<<0);
		_delay_ms(3);
 
		PORTD&=~(1<<0);
		PORTD&=~(1<<1);
		PORTC=SSD[cnt%10];
		PORTD|=(1<<1);
		_delay_ms(3);
 
		//Input Testing
		if ((PIND&0x80)==0)
		{
			//while((PIND&0x80)==0);
			cnt++;
			_delay_ms(250);
		}
		if(cnt>=60) cnt=0;
    }
}
 
 

Click here to download source file.

Schematic diagram

A DIY Timer/Scheduler and temperature controller using PIC16F876A

Introduction

A timer is useful in any task that requires a specific time or a duration that the target device will turn on and off. It is easily found at low price. For electronic hobbyists, a timer can easily be created using a typical timer IC NE555 with other dozen of components.

Here I design a timer using a small microcontroller - PIC16F876A. It's suitable to handle timing setting, displaying, controlling, and scheduling. 

Main menu of this timer

This timer can handle the following tasks:

1. Main menu - displaying date/time, and temperature
2. Date/Time setting
3. Short 16 hours timer
4. Temperature setting for an output relay
5. Scheduling daily on time of timer relay

Day of Week Adjust

Time Adjust

Date Adjust

Short timer up to 16 hours

Temperature Adjusting for output relay

Daily On Time Adjusting

Design

Firmware

I use MicroC Pro PIC to program this device. The operation of this device become abnormal whenever I try to add more function in C source code. So I tried to optimize, reduce, and test this project as much as I can to make the operation more stable.

Listing below is the source code for v1.2 of this project.

 
#include "board.h"
 
void main() {
     LCD_Set();
     DS1307_Init();
     T_Init();
     TMR0_SETUP();
     SCH_READ();
     while(1){
              Menu_Scan();
              Selector();
              SCH_RUN();
     }
}

We can only see a dozen lines of code, as they are separated in different files. Click here to download firmware and design file.

Hardware

I designed this project using Proteus 8. This program also allow us to simulate.

Schematic

Circuit board is very simple. It can be made using toner transfer method.

PCB design view

Copper track

Top silk

Design view in 3D

Idle

Top Side

Bottom Side