Connecting a 4x3 keypad to PIC16F877A

Hi,
I have a 4x3 keypad that i would like to connect to a PIC16F877A. I understand that i have to use some pullup resistors connecting at the rows. I have seen different versions in the forum as to how to connect.
I am connecting to Port C0-C6 of the PIC. I had already use 10kohms resistor connecting to the rows then directly to the PIC.
Is this correct?

Hi,

This tutorial might help PIC Tutorial* Nine - HEX Keypad

It is better to use PORTB of PIC16F877A for the purpose because you can utilize the interrupt on change capability of the PORTB . Also, you can activate the internal pull up s....

Try this lesson with free C code and video, Keypad Lesson.

The MCD2 DemoBoard2 (Pic16.com) I have has a key matrix on it.... As a start there is code comes with it for this function, and full schematics available.. Easily downloadable it might be a reasonable start for you buddy..

Use PORTB if it is spare, but you only need 4 pullups (1kish) so don't worry about sticking to PORTB if you need other functions of it (SSP/serial/etc). WPUB (or nRBPU) is the pullup control (0=On) if you use PORTB, but I always try and save it if I can. You can make your code call functions in a "psuedo" interrupt way if you want notification of key-change if you needed it to....

Kind regards
NEAL

Worth a look,
NEAL

Hi guys, Thanks for all the information and help.

After going through the links, i found that the pull up resistors are connected to the columns instead. I am getting confused on this.

engshahrul said:

Try this lesson with free C code and video, Keypad Lesson.

Click to expand...

Hi shahrul,

Thanks for the useful guide. I managed to display the numbers keyin on the lcd.

Now i have a problem. I need to compare the keyin values against the readings from a sensor. I am unable to display the keyin numbers.

Please do help me on this.

ah_loon said:

Hi shahrul,

Thanks for the useful guide. I managed to display the numbers keyin on the lcd.

Now i have a problem. I need to compare the keyin values against the readings from a sensor. I am unable to display the keyin numbers.

Please do help me on this.

Click to expand...

If you can't display keypad values, maybe you are problem on LCD code.

engshahrul said:

If you can't display keypad values, maybe you are problem on LCD code.

Click to expand...

hi shahrul,

i am not sure where went wrong. maybe is the codes. could you help me on this?

as follow is the portion.
while(1)
{ //keypad scanning
clearrow1(); //Clear 1st output pin and set the others
scancolumn1(); //scan column 1-4
clearrow2(); //Clear 2nd output pin and set the others
scancolumn2(); //scan column
clearrow3(); //Clear 3rd output pin and set the others
scancolumn3(); //scan column
clearrow4(); //Clear 4th output pin and set the others
scancolumn4(); //scan column

if(num_count==2)
{

while(1)
{
//lcd_clr();
lcd_goto(0); //cursor start from beginning

//display character on LCD
send_char(' ');
send_char('S');
send_char('P');
send_char('E');
send_char('C');
send_char('.');
send_char('.');
send_char('=');

lcd_goto(20); //cursor go to 2nd line of the LCD

//display character on LCD
send_char(' ');
send_char('M');
send_char('E');
send_char('A');
send_char('S');
send_char('U');
send_char('R');
send_char('E');
send_char('D');
send_char('=');


while(1) //infinity loop
{

//tempA=temp;
//tempA=440;
lcd_goto(9);
keyin[2]=tempA;
dis_num(keyin[2]);
//dis_num((unsigned long)round(tempA));
send_char(0b11011111); //to set in degree celcius
send_char('C');
send_char(' ');
send_char(' ');

I don't like checking someone code. But, I see why so many while(1). If the program doing while(1), it will not do the others while(1)