Matrix Keypad Interface With PIC Microntroller
Metric keypads use in various types of embedded applications like door lock system, phones, as input devices etc. We can reduce numbers of pins by using metric keypad instead to individual keys. Matrix keypad (4x3) have 12 buttons and we can scan all of button with 7 microcontroller pins.
Circuit Diagram
In the example circuit, we are using a keypad and a LCD (16x2) for display the value when anyone keypad key pressed. Only single key can be scan at a time.
If you have any question, ask feel free. I will totally devoted for your help.
Matrix Keypad scanning algorithm
In the normal condition when no key is pressed, all columns (c-0 to c-2) read low. When any key is pressed the specific column goes high.
When microcontroller find any column pin high, then scanning algorithm works. For example column-3 is high, First controller low first row pin and scan that column-3 is still high or not. Controller turn low row pins one by one until column-3 pin does not go low. Once the row has been identified, the specific
column of the pressed key can be established by locating
the position of the single low bit on the input port.
Codes
#include<p18f2520.h>
#define
RS_PIN PORTAbits.RA1 /* Pin for RS */
#define
E_PIN PORTAbits.RA0 /* Pin for E */
//--------------------------------------------------------------------------
void
LCD_Init(void);
void
Str_LCD( const rom char *buffer);
void
Chr_LCD(char data);
void
Clear_LCD(void);
void
Move_Corsor( char Line, char Pos);
//--------------------------------------------------------------------------
void
Time_10ms(void);
void
scan_keypad(void);
void main()
{
TRISA=0x00;
TRISB=0x07; //
Set row pins as output and Column pins as input
TRISC=0x00; //
Output port for LCD
PORTA=0X00;
PORTB=0X78; //
High to Row pins
PORTC=0x00;
ADCON1 = 0x0F; //
Set all AN pins as digital
T0CON = 0x06; // Timer-0 for
LCD
LCD_Init();
Str_LCD("Waiting for
key");
while(1)
{
scan_keypad();
}
}
void
Time_10ms()
{
TMR0H=0xFE;
TMR0L=0x7A;
T0CONbits.TMR0ON=1;
while(INTCONbits.TMR0IF==0);
T0CONbits.TMR0ON=0;
INTCONbits.TMR0IF=0;
}
void
LCD_Init()
{
RS_PIN=0; //LCD instructions
Chr_LCD(0x38); //LCD 8 Bit Data
Chr_LCD(0x01); //LCD clear
Chr_LCD(0x0C); //LCD
diplay on cursor not blinking
Chr_LCD(0x80); //LCD cursor Pos.
begain
RS_PIN=1; //LCD DATA
}
void
Str_LCD( const rom char *buffer)
{
while(*buffer) // Write
data to LCD up to null
{
Chr_LCD(*buffer); // Write character to LCD
buffer++; // Increment
buffer
}
}
void
Chr_LCD(char data)
{
PORTC=data;
E_PIN=1;
Time_10ms();
Time_10ms();
E_PIN=0;
Time_10ms();
Time_10ms();
}
void
Clear_LCD(void)
{
RS_PIN=0;
Chr_LCD(0x01);
Chr_LCD(0x80);
RS_PIN=1;
}
void
Move_Corsor( char Line, char Pos)
{
RS_PIN=0;
if(Line==1)Chr_LCD(0x80);
if(Line==2)Chr_LCD(0xC0);
while(Pos!=0)
{
Chr_LCD(0x14);
Pos--;
}
RS_PIN=1;
}
void
scan_keypad()
{
if(PORTBbits.RB0==1) // Scan column-0
{
Clear_LCD();
PORTBbits.RB3 =
0;
if(PORTBbits.RB0==0)
Str_LCD("You pressed \"1\"");
else
{
PORTBbits.RB4=0;
if(PORTBbits.RB0==0)
Str_LCD("You pressed \"4\"");
else
{
PORTBbits.RB5=0;
if(PORTBbits.RB0==0)
Str_LCD("You pressed \"7\"");
else
{
PORTBbits.RB6=0;
if(PORTBbits.RB0==0)
Str_LCD("You pressed \"*\"");
}
}
}
}
if(PORTBbits.RB1==1) // Scan column-1
{
Clear_LCD();
PORTBbits.RB3 =
0;
if(PORTBbits.RB1==0)
Str_LCD("You pressed \"2\"");
else
{
PORTBbits.RB4=0;
if(PORTBbits.RB1==0)
Str_LCD("You pressed \"5\"");
else
{
PORTBbits.RB5=0;
if(PORTBbits.RB1==0)
Str_LCD("You pressed \"8\"");
else
{
PORTBbits.RB6=0;
if(PORTBbits.RB1==0)
Str_LCD("You pressed \"0\"");
}
}
}
}
if(PORTBbits.RB2==1) // Scan column-2
{
Clear_LCD();
PORTBbits.RB3 =
0;
if(PORTBbits.RB2==0)
Str_LCD("You pressed \"3\"");
else
{
PORTBbits.RB4=0;
if(PORTBbits.RB2==0)
Str_LCD("You pressed \"6\"");
else
{
PORTBbits.RB5=0;
if(PORTBbits.RB2==0)
Str_LCD("You pressed \"9\"");
else
{
PORTBbits.RB6=0;
if(PORTBbits.RB2==0)
Str_LCD("You pressed \"#\"");
}
}
}
}
PORTB=0X78; //
Set again to Row pins
}
Download Project file :- https://drive.google.com/file/d/0B886Kbl42IVuaVF6UTBTYmxpN3M/view?usp=sharing
If you have any question, ask feel free. I will totally devoted for your help.
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