4x4 key pad programing - please help

Hi all. I'm trying to make each button of a 4x4 keypad display 4 letters. For example when I click once it should display 1. If twice it should display A.... etc., like a mobile keypad. Can anyone help me with how to write a program using 8051, please?

answer

l think you have to asked MR.Omar about this 4x4 display

MOD_EDIT: Useless post and foul language.

mhh

i think you should just count pulses in a time schedule for example:
i=0
Do while time < time + 1second

if button press = true then

if i = 0 then
"1"
i=1
elseif i=1 then
"A"
i=2
elseif i = 2 then
"B"
i=3
elseif i= 3 then
"C"
end if

end if


Loop

after the second or what ever the do while will be exited and the sources given to the next character

untherstand?/

Tks

the problem is that im using the assembly language. But i got the idea of what you wrote. i will try write a program with assembly language using your idea.

thank you very much tks.

Hiya Soul,
Since your using assembly check out Nigel's tutorials if you haven't yet, 1 section deals with a 4x4 keypad and coupled with all the other tutorials it's one of the best guides to pic programming in assembly on the net.

Cheers Bryan

i will try it

thank you bryan1

yeah,

i wrote it also with the idea that you should convert it to ASM.

Anyway i think to explain this kind of Tricks the best thing is to do it in basic because else you will see some strange words and maybe you loose the clue.


You could easyly add in this loop for every button the If else structure.

the i you could it been using always, the only thing is that the second counter will be needed to be able to change the cursor,

if you are a god with asm you could make it all with lookup tables, it would make the system short of code.

with that idea in mind you only Lookup the Key number and then you automaticly calculate the i values and the next key value.

Sow with one Loop you could easyly do all the keys!!

Tks

yes TKS, i made a program with asm to display one character using one button. so now i will try to apply your idea and see if i can display more character using one button.

thank you TKS

First of all the hardware:
You need 1 port to control your keypad
I connect my keypad as follow
Column 0 to pin n.0
Column 1 to pin n.1
Column 2 to pin n.2
Column 3 to pin n.3

Row 0 to pin n.4
Row 1 to pin n.5
Row 2 to pin n.6
Row 3 to pin n.7
Where n is a number between 0 and 3, the ports of a 8051 :wink:

Every row has a pull-up resistir of 100k to Vcc so that these 4 inputs always are high.

The µC drives sequentially the for columns high. After each column it checks if one of the rows is low due to a key-press by the user.
No keys pressed: all rows high (remember the pull-up R).
One Key pressed: One row is low.
The combination of the activated Column and the Row with a low signal is unique for every key.

The assembler software........... later on :lol:

And now the software...

See this file as a subroutine.
You don't need to change anything to it.
Define the variables "KP_AsciiTable", "KeyPadAddress" and "KeyctrDebounce" in your main routine.

Call the routine "KP_Start" at regular time interval (use a timer interrupt routine) and check the variables "KeyRead", "KeyCode" and "KeyAscii" in your main code.
If "KP-Start" has detect a key, it will write the appropriate data in these three variables.
Do not forget to clear the "KeyRead" bit when you processed a key in your main code!!

If there's something unclear let me know... :shock:

And now with the file...

Thank you very much mcs51mc.

im looking forward to it :wink: , because im really stuck at this point :cry:

thank you again

thank you mcs51mc.

the assembler is mixed up, but i will try to understand it.

thank you my friend

A little bit more code that (maybe) will help U understand the previous one :lol:

At the start you will find the declaration of some constants KeyPadAddress to Key_F. If you have other keys on your keypad change the name but not the data. e.g. If the key in col3 row3 is * instead of F, change the name Key_F to Key_Star but leave the data 000Fh unchanged.

Part 1: contains the endless loop.
If bit KeyRead is not set, there's no key pressed by the user so you can skip all the key stuff and do other things from LBL_001 on.
When the user press a key, the KeyPad module will set bit KeyRead and then you can jump into the key stuff (part 2).

Part 2: do key depending stuff
The KeyPad module writes a number from 0 to F into variable KeyCode depending on the pressed key. By comparing that variable with all the Key_0 to Key_F constants you will know what key is pressed.
Note that you don't need to check all the keys. If at a certain point in your programm you are interrested in keys 0 to 9, C and E, just check these keys only.
But don't forget to clear the KeyRead bit at the end!!!

Last Part:
Has to remain the last part in you program. The KeyPad module place an ascii character from that list into variable KeyAscii. Again, if the key in col3 row3 is * instead of F, replace that string by '0123456789ABCDE*'.
If you have an LCD in your project, you can write that variable directly to your LCD.


In the timer interrupt routine you need only one line of code for the KeyPad module: Because the module use the datapointer you have to push it onto the stack.


Remember, if your compiler understand all the definitions in the KeyPad module, you don't have to change anything in that file. Just use it as a black box in all your future projects.

Have fun ...

thank you mcs51mc for your support

I have done the same with computer parallel port. I think u can use the same source codes.

refer page77 of
for line follower

refer page96
MY EXPERIENCE IN PARALLEL PORT INTERFACING
you can get it from yahoo group-booksbybibin
http://groups.yahoo.com/group/booksbybibin/

comments about this book
http://www.booksbybibin.blogspot.com/

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