Ibrahim Dogan - Advanced PIC Microcontroller Projects in C

{

case Plus:

Calc = Op1 + Op2; // If ADD

break;

case Minus:

Calc = Op1 - Op2; // If Subtract

break;

case Multiply:

Calc = Op1 * Op2; // If Multiply

break;

case Divide:

Calc = Op1 / Op2; // If Divide

break;

}

LongToStr(Calc, op); // Convert to string in op

//

// Remove leading blanks

//

j=0;

for(i=0;i<=11;i++) {

if (op[i] != ' ') // If a blank

{

lcd[j]=op[i];

j++;

}

}

Lcd_Out_Cp(lcd); // Display result

Delay_ms(5000); // Wait 5 seconds

Lcd_Cmd(LCD_CLEAR);

}

}

Figure 6.48: Program listing

Function getkeypad receives a key from the keypad. We start by sending a 1 to column 1, and then we check all the rows. When a key is pressed, a logic 1 is detected in the corresponding row and the program jumps out of the while loop. Then a for loop is used to find the actual key pressed by the user as a number from 0 to 15.

It is important to realize that when a key is pressed or released, we get what is known as contact noise, where the key output pulses up and down momentarily, producing a number of logic 0 and 1 pulses at the output. Switch contact noise is usually removed either in hardware or by programming in a process called contact debouncing. In software the simplest way to remove the contact noise is to wait for about 20ms after a switch key is pressed or switch key is released. In Figure 6.46, contact debouncing is accomplished in function getkeypad .

In the program listing in Figure 6.48, a function called getkeypad has been developed to read a key from the keyboard. The mikroC language has built-in functions called Keypad_Read and Keypad_Released to read a key from a keypad when a key is pressed and when a key is released respectively. Figure 6.49 shows a modified program (KEYPAD2.C) listing using the Keypad_Released function to implement the preceding calculator project. The circuit diagram is the same as in Figure 6.46.

/**************************************************************

CALCULATOR WITH KEYPAD AND LCD

==============================

In this project a 4 x 4 keypad is connected to PORTB of a PIC18F452

microcontroller. Also an LCD is connected to PORTC. The project is a simple

calculator which can perform integer arithmetic.

The keys are labeled as follows:

1 2 3 4

5 6 7 8

9 0 Enter

+ − * /

In this program mikroC built-in functions are used.

Author: Dogan Ibrahim

Date: July 2007

File: KEYPAD2.C

**************************************************************/

#define Enter 12

#define Plus 13

#define Minus 14

#define Multiply 15

#define Divide 16

//

// Start of MAIN program

//

void main() {

unsigned char MyKey, i,j,lcd[5],op[12];

unsigned long Calc, Op1, Op2;

TRISC = 0; // PORTC are outputs (LCD)

//

// Configure LCD

//

Lcd_Init(&PORTC); // LCD is connected to PORTC

Lcd_Cmd(LCD_CLEAR);

Lcd_Out(1,1, "CALCULATOR"); // Display CALCULATOR

Delay_ms(2000);

Lcd_Cmd(LCD_CLEAR);

//

// Configure KEYPAD

//

Keypad_Init(&PORTB); // Keypad on PORTB

//

// Program loop

//

for(;;) // Endless loop

{

MyKey = 0;

Op1 = 0;

Op2 = 0;

Lcd_Out(1,1, "No1: "); // Display No1:

while(1) {

do // Get first number

MyKey = Keypad_Released();

while(!MyKey);

if (MyKey == Enter) break; // If ENTER pressed

if (MyKey == 10) MyKey = 0; // If 0 key pressed

Lcd_Chr_Cp(MyKey + '0');

Op1 = 10*Op1 + MyKey;

}

Lcd_Out(2,1, "No2: "); // Display No2:

while(1) // Get second no

{

do

MyKey = Keypad_Released(); // Get second number

while(!MyKey);

if (MyKey == Enter) break; // If ENTER pressed

if (MyKey == 10) MyKey = 0; // If 0 key pressed

Lcd_Chr_Cp(MyKey + '0');

Op2 = 10*Op2 + MyKey;

}

Lcd_Cmd(LCD_CLEAR);

Lcd_Out(1,1, "Op: "); // Display Op:

do

MyKey = Keypad_Released(); // Get operation

while(!MyKey);

Lcd_Cmd(LCD_CLEAR);

Lcd_Out(1,1, "Res="); // Display Res=

switch(MyKey) // Perform the operation

{

case Plus:

Calc = Op1 + Op2; // If ADD

break;

case Minus:

Calc = Op1 - Op2; // If Subtract

break;

case Multiply:

Calc = Op1 * Op2; // If Multiply

break;

case Divide:

Calc = Op1 / Op2; // If Divide

break;

}

LongToStr(Calc, op); // Convert to string

//

// Remove leading blanks

//

j=0;

for(i=0;i<=11;i++) {

if (op[i] != ' ') // If a blank

{

lcd[j]=op[i];

j++;

}

}

Lcd_Out_Cp(lcd); // Display result

Delay_ms(5000); // Wait 5 seconds

Lcd_Cmd(LCD_CLEAR);

}

}

Figure 6.49: Modified program listing

Before using the Keypad_Released function we have to call the Keypad_Init function to tell the microcontroller what the keypad is connected to. Keypad_Released detects when a key is pressed and then released. When released, the function returns a number between 1 and 16 corresponding to the key pressed. The remaining parts of the program are the same as in Figure 6.48.

Serial communication is a simple means of sending data long distances quickly and reliably. The most common serial communication method is based on the RS232 standard, in which standard data is sent over a single line from a transmitting device to a receiving device in bit serial format at a prespecified speed, also known as the baud rate, or the number of bits sent each second. Typical baud rates are 4800, 9600, 19200, 38400, etc.