10x4 matrix keyboard using only portB

[aratti]

Darel be patient next release will be with "PORTB change interrupts". For that I need to build a new hardware prototype and it will take few days.
I had to fix the bug you pointed out quickly, otherwise I could not sleep!

Regards

Al.

[falingtrea]

If I am looking at this correctly, the one drawback to this design is that you can't detect multiple keypresses in the sam row, right? In fact, holding two keys down in the same row could cause the wrong character code to be generated. Like holding down 1,1,and 1,8 gives you the code for 1,9, right? Not trying to nitpick. Just wanted to make sure I understood the advantages and disadvantages to the design.

[aratti]

Yes Tim, this is the price you have to pay for the extra keys!

If the spacing of the keypad is done properly than chances to press two contiguous keys at the same time are really rare, but since number of keys available is no more an issue, you can dedicate one key to delate the possible unwanted input.

Al.

[T.Jackson]

I believe that a protocol is possible to detect simultaneous key presses, BUT it would fail if both keys were pressed at exactly the same time (incredibly unlikely though). However, if it did occur -- the procedure would return the key that equated to the binary sum of the two keys held down.

You would only need microseconds of a difference between the keys being pressed to come up with something that works.

Trent Jackson

[Ioannis]

Since we are talking about mechanical switch, that micro seconds might be to short time in my opinion. Debouncing is needed to read the switch correctly.

Ioannis

[T.Jackson]

Moreover ...

I think if the columns were each given a unique, physical delay, say using an RC circuit -- you'd eliminate the possibility of two keys ever being processed as one.

[aratti]

Following T.Jackson suggestion, I removed the auto-repeat, now multiple keys have to close exactly at the same time to be decoded as the sum. This has been accomplished introducing a WHILE WEND which detect when you release the key.

To follow the code.

Al.

'****************************************************************
'*  Name    : 60 Keys_Kpad.BAS                                  *
'*  Author  : [a.ratti]                                         *
'*  Notice  : Copyright (c) 2008                                *
'*          : All Rights Reserved                               *
'*  Date    : 20/11/2008                                        *
'*  Version : 2.2                                               *
'*  Notes   :           Micro used: Pic 16F84a                  *
'*          : The software will decode any matrix keypad 4 x n  *
'*          :    where n is any columns number from 1 to 15     *
'****************************************************************

TrisA = %00000000
TRISB = %11111111

Define OSC 4

'--- EEprom ASCII code assignment to define keys response ---------

'------------------- First Row --------------------
Eeprom 1,[49,50,51,52,53,54,55,56,57,48,43,40,94,91,27]' (1,1)-(1,15)

'--------------------Second Row --------------------
Eeprom 16,[65,66,67,68,69,70,71,72,73,74,45,41,37,93,26]' (2,1)-(2,15)

'--------------------- Third Row ------------------
Eeprom 31,[75,76,77,78,79,80,81,82,83,84,47,64,36,60,62]' (3,1)-(3,15)

'--------------------- Fourth Row ------------------
Eeprom 46,[85,86,87,88,89,90,46,58,59,61,42,35,38,32,13]' (4,1)-(4,15)
'------------------------------------------------------------------



'--------------------------- Set variables and pins --------------------

LED         VAR PortA.0     ' Heart beating led
Buz         var PortA.1     ' got character acknowledgement
Tx          var PortA.2     ' Serial out
RTS         var portA.3     ' Ready to sent when low
T9600       con 2           ' baud rate = 9600

UCase       var byte
KeyFlag     var byte
KbOut       var Byte    [2] ' Buffer Array 

high Tx                     ' purge serial line (True Mode)
High RTS                    ' disable RTS
low Buz                     ' Bepper off

KeyFlag = 0                 ' reset variable
Ucase = 0                   ' set uppercase


'-------------------------- Main program -------------------------------

 Loop:
 if KeyFlag>0 then           'If <> 0 then Tx ASCII character and Beep
 Low RTS                     'RTS flag enabled
 pause 20
 
 if KbOut[1]=26 then Loop    'Skip ascii code 26
 
 If KbOut[1]=>65 then        'Skip ascii code <> character 
 KbOut[0] = KbOut[1] + UCase 'If UCase = 0 then UpperCase 
 else
 KbOut[0] = KbOut[1]
 endif
 
 '---------------------------------------------------------------------
 Serout Tx,T9600,[KbOut[0]]  ' Tx ascii character 
 '----- Choose one of the two serout comand DON'T SELECT BOTH !!! -----
 'Serout Tx,T9600,[#KbOut[0]]  ' Tx ascii code 
 '---------------------------------------------------------------------
 
 High RTS                   ' RTS flag disabled
 high buz                   ' Beep on 
 pause 30                   ' time duration of the beep
 low Buz                    ' Bepper off
 pause 150
 endif
 pause 50                   ' Heart beating frequency
 toggle Led                 ' Heart beating
 
 while KeyFlag>0            ' stop auto repeat
 KeyFlag = PortB
 KeyFlag=KeyFlag & %00001111
 wend 
 
 '----------------------------- KeyScan routine ------------------------
 
 KeyFlag=0                  ' reset flag variable
 
 '------------------------ First Row - keys from 1 to 15  --------------
 TRISB = %11101111
 PortB =16
 If PortB>16 then           ' one key of the first row has been pressed
 KeyFlag=PortB 
 KeyFlag=KeyFlag & %00001111  ' decode to which column the key belongs 
 Gosub GetChar
 goto Loop
 endif
 
 '------------------------ Second Row - keys from 16 to 30 -------------
 TRISB = %11011111
 PortB =32
 If PortB>32 then           ' one key of the second row has been pressed
 KeyFlag=PortB
 KeyFlag=KeyFlag & %00001111
 KeyFlag = KeyFlag +15      ' decode to which column the key belongs
 gosub GetChar
 goto Loop
 endif
 
 '----------------------- Third Row - keys from 31 to 45 ---------------
 TRISB = %10111111
 PortB =64
 If PortB>64 then           ' one key of the third row has been pressed
 KeyFlag=PortB
 KeyFlag=KeyFlag & %00001111
 KeyFlag = KeyFlag +30      ' decode to which column the key belongs
 gosub GetChar
 goto Loop
 endif
 
 '------------------------ Fourth Row - keys from 46 to 60 -------------
 TRISB = %01111111
 PortB =128
 If PortB>128 then          ' one key of the fourth row has been pressed
 KeyFlag = PortB
 KeyFlag=KeyFlag & %00001111
 KeyFlag = KeyFlag +45      ' decode to which column the key belongs
 gosub GetChar
 endif
 
 goto Loop
 
 '------------------------ End of keyscan routine ----------------------
 
 
 '----------------------------------------------------------------------
 '---------------- Select Uppercase or LowCase letters -----------------
 '------ (Ucase = 32 then lowerCase)  (UCase = 0 then UpperCase) -------
 '----------------------------------------------------------------------
 GetChar: ' Read ASCII code from eeprom & set UCase or LCase
 Read KeyFlag, KbOut[1]
 If  KbOut[1]=26 then
 If UCase=0 then
 Ucase=32
 else
 UCase=0
 endif
 endif
 return
 
 
 end

[falingtrea]

I found this reference on another forum that was very interesting. I had never heard of Charlieplexing before but this is really cool. It not only applies to multiplexing outputs, but inputs as well. Since the guy that came up with this works at Maxim, there are even some Maxim parts that use charlieplexing to drive LEDs. It looks like aratti's design may be a variant of charlieplexing.