Activity 3. Simple calculator
This activity uses a 4x4 keypad and a LCD 16x2, with the aim of making the PIC18F4550 a simple calculator that can perform 4 basic operations between 2 single-digit numbers.
(75 minutes)
Activity 3
The PIC18F4550:
- reads the first number
- reads which mathematical operation will be performed (+, -, X, /)
- reads the second number
- displays the result on the LCD
- waits for ‘C’ to be pressed to start the process from the beginning
Step 1. The circuit is drawn at the Proteus Design Suite.
Step 2. The program in C language is written.
Write in CCS C Compiler the program in C language
#include <main.h> // the file main.h with the
// initial settings is included.
// This file must be placed in the same
// folder with the project.
// Also the 18F4550.h file must exist
// in the same folder with the project
#include <flex_lcd.h> // The h file of the lcd driver
// should be in the same folder where we will save our program.
// The #define LCD_DB4 PIN_B4 etc statements in flex_lcd.c
// should be checked and possibly modified.
// These statements determine the pins of the microcontroller
// that are connected to LCD 16x2.
#include <keypad.h> // The h file of the keypad driver
// should be in the same folder where we will save our program.
// The #define row0 PIN_B4 etc statements in keypad.h
// should be checked and possibly modified.
// These statements determine the pins of the microcontroller
// that are connected to the keypad 4x4.
#byte PORTB =0xF81
// We attribute to the memory position 0xF81 the name PORTB.
// This means that we define a 8 bit variable whose value
// will be stored to the memory position F81h.
// The memory position F81h is the PORTD data register.
#byte PORTD=0xF83 // F83h is the position or PORTD data register
// at the data memory of the microcontroller
// SFR Special Function Register
char key; //variable to save keypad's characters
int num1=10; //variable for the first number
int num2=10; //variable for the second number
char operation; //variable for the operation
float result; //variable for the result
boolean flag=0; //flag raised when the divider is 0
//this function converts keypad's character to integer
int convert_to_number(char c);
// ********* main program ************************
void main() {
set_tris_d(0x00); //PORTD is defined as output - LCD 16x2
kbd_init(); //initialization routine for the keypad 4x4
lcd_init(); //initialization routine for the LCD 16x2
lcd_putc("\f"); //clear the screen
while(TRUE){
//read the first number
do{
//wait until a key is pressed
key=kbd_getc();
if(key!=0){
//call the "convert_to_number"
num1=convert_to_number(key);
}
}
while(num1>9);
//print the first number
printf(lcd_putc,"%d",num1);
//read the operation
do{
//wait until a key is pressed
operation=kbd_getc();
}
while(operation!='X' && operation!='/' && operation!='+' && operation!='-');
//print the operation
if(operation=='+'){
printf(lcd_putc," + ");
}
else if(operation=='-'){
printf(lcd_putc," - ");
}
if(operation=='X'){
printf(lcd_putc," * ");
}
else if(operation=='/'){
printf(lcd_putc," / ");
}
//read the second number
do{
//wait until a key is pressed
key=kbd_getc();
if(key!=0){
//call the "convert_to_number"
num2=convert_to_number(key);
}
}
while(num2>9);
//print the second number
printf(lcd_putc,"%d = ",num2);
//calculate the result
if(operation=='+'){
result=num1+num2;
}
else if(operation=='-'){
if(num1>num2){
result=num1-num2;
}
else{
result=num2-num1;
printf(lcd_putc,"-");
}
}
else if(operation=='X'){
result=num1*num2;
}
else if(operation=='/'){
if(num2==0){
flag=1;
}
else{
result=(float)(num1)/num2;
}
}
if(flag==1){ //divider = 0
flag=0;
printf(lcd_putc,"\nUndefined");
}
else{
//print the result
printf(lcd_putc,"%f",result);
}
//wait until the "C" is pressed
do{
key=kbd_getc();
}
while(key!='C');
//clear the LCD
lcd_putc("\f");
num1=num2=10;
}
}
//this function converts keypad's character to integer
int convert_to_number(char c){
if(c=='0'){
return 0;
}
else if(c=='1'){
return 1;
}
else if(c=='2'){
return 2;
}
else if(c=='3'){
return 3;
}
else if(c=='4'){
return 4;
}
else if(c=='5'){
return 5;
}
else if(c=='6'){
return 6;
}
else if(c=='7'){
return 7;
}
else if(c=='8'){
return 8;
}
else if(c=='9'){
return 9;
}
else if(c=='/'){
return 10;
}
else if(c=='X'){
return 11;
}
else if(c=='-'){
return 12;
}
else if(c=='+'){
return 13;
}
else if(c=='='){
return 14;
}
else if(c=='C'){
return 15;
}
else{
return 16;
}
Step 3. Compile the program in order to create the hex.file (program in machine code). Load the program (hex.file) to the microcontroller.
Step 4. Run the simulation and check the correct operation of the circuit.
Step 5. Suggested modifications and discussion:
Tip.
#include <math.h>, pow(), sqrt()