Keypad interfacing to PIC contoller

[shrihari]

Dear all,

Hi to all,

My query is, recently i tried to interface 4x4 matrix keypad to the PIC16f877a controller and i found that my keypad buttons are getting automatically pressed whenever i make movement of keypad, to resolve and crosscheck this problem i have purchased a new keypad but still it is giving same problem. i hope the problem may be inside the keypad, but i don't know exactly what is the problem. If any one can suggest remedy to my problem i will be very thankful to him.

 

[Arouse1973]

Can you post a circuit diagram? And your code?
Thanks Adam

 

[shrihari]

Circuit Diagram:

The connector shown above is directly connected to PORT of PIC controller without connecting rows or columns to Vcc supply via resistors. I have used same keypad as showed in figure above.

My program is: The code is for only first row of keypad remaining rows are also giving the same problem.


#include <stdio.h>
#include <stdlib.h>

/*
*
*/
#include"newfileR.h"
void delay();
void lcd_cmd(int);
void lcd_data(int);
#define rs RC0
#define rw RC1
#define en RC2
#define r0 RD7
#define r1 RD6
#define r2 RD5
#define r3 RD4
#define c0 RD3
#define c1 RD2
#define c2 RD1
#define c3 RD0


void main(){
TRISB=0x00;
TRISC=0x00;
TRISD=0x0F; //row as output and column as input
PORTD=0x00;
PORTB=0x00;
PORTC=0x00;


ADCON1=0x80;
ADCON0=0x01;
ADIF=0;
lcd_cmd(0x38);
lcd_cmd(0x0C);
lcd_cmd(0x01);
lcd_cmd(0x80);

while(1){
lcd_cmd(0xC0);
r0=1;r1=0;r2=0;r3=0; // First Row
if(c0==1&&c1==0&&c2==0&&c3==0){
lcd_data(0x31);
while(c0==1&&c1==0&&c2==0&&c3==0);
}
if(c0==0&&c1==1&&c2==0&&c3==0){
lcd_data(0x32);
while(c0==0&&c1==1&&c2==0&&c3==0);
}
if(c0==0&&c1==0&&c2==1&&c3==0){
lcd_data(0x33);
while(c0==0&&c1==0&&c2==1&&c3==0);
}
if(c0==0&&c1==0&&c2==0&&c3==1){
lcd_data('A');
while(c0==0&&c1==0&&c2==0&&c3==1);
}


}
}
void delay(){
for(j=0;j<4000;j++);
}
void lcd_cmd(int cmd){
PORTB=cmd;
rw=0;
rs=0;
en=1;
for(i=0;i<120;i++);
en=0;
for(i=0;i<120;i++);
}
void lcd_data(int data){
PORTB=data;
rw=0;
rs=1;
en=1;
for(i=0;i<120;i++);
en=0;
for(i=0;i<120;i++);
}

 

[BobK]

Bad design. First of all, pushing two buttons in the same column will short a low output to a high output.

But the problem you are seeing is because the input are floating when no button is pressed. You need a pullup resistor on each column. Then you need to change the row scanning to make only one row and output and put a zero on it, while the other rows are made to be inputs (I.e. by setting TRIS). Now when you push a button, you will see a zero on the column for that button when the row for that button is selected, and you will see a 1 in that column otherwise.

Bob

 

[Emam]

Is this meaning that the problem is mechanical rather than electrical?
Can we put some filters somewhere to avoid this problem?

 

[BobK]

No, the problem is electrical and I told you how to solve it.

Bob