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freedom
Joined: 10 Jul 2011
Posts: 54
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| Sharing/multiplexing GLCD (128X64) data pin with keypad |
 Posted: Sat Nov 22, 2014 12:15 am |
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Hello every one,
I search in this forum and google for LCD and keypad multiplexing.
I found 4X20 and 2X16 lcd display are multiplexed with 4X4 keypad.
They used 4 data pins of lcd with 4 pins of keypad (also use diode), and the rest 4 pins of keypad are connected to another pins of micro controller.
As GLCD (128X64) used 8 data pins for operation, can I use these 8 data pins for 4X4 keypad ?
Or any other solution for Glcd and keypad, so that we can minimize the I/O pins requirement for this.
Thanks |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19552
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| Posted: Sat Nov 22, 2014 1:55 am |
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The way the multiplexing is done, is that with the diodes, when there is no input drive on a 'line' of the keypad (from the other pins), the 'output' side of the keypad does nothing - the diode allows it to go high or low whatever is happening on the keypad. This allows these four lines of the keypad to be used when this is the case, for other things like driving an LCD. This approach can be applied to any line, provided it is not 'in use' when the keypad is being scanned.
So, potentially, yes. You could use four of the LCD data lines as the lines to read the keypad. You could save another pin, if instead of using four output pins on the PIC to drive the LCD, you used two lines feeding a 2-4 line decoder. Then (being sneaky), used a bit of logic, so this is only enabled when both the GLCD CS lines are low. Done like this you could have a keypad using only two extra wires.
However remember this means that the timing of your code _must_ ensure that keypad scans and LCD I/O are always done at separate times. |
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temtronic
Joined: 01 Jul 2010
Posts: 9246
Location: Greensville,Ontario
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| Posted: Sat Nov 22, 2014 8:54 am |
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If you want to be really,really sneaky( and frugal), you only need ONE wire to read a 4by4 kpd! By proper selection of resistors on the row and columns of the kpd you create a 'resistive divider', then read a key pressed' by reading the analog voltage.
Of course you need a free analog input pin on the PIC.
This was done a long,long time ago when techs had to be 'creative'.
just another way to do it.
hth
jay |
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anglab
Joined: 27 Sep 2010
Posts: 4
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| Posted: Sat Nov 22, 2014 6:39 pm |
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Hi,
I use this schematic and driver.
| Code: |
PIC KBD GLCD
18F4620 4X4 AG-12864
------------------------
RD0 R1 ROW1 DB0
RD1 R2 ROW2 DB1
RD2 R3 ROW3 DB2
RD3 R4 ROW4 DB3
RD4 |< COL1 DB4
RD5 |< COL2 DB5
RD6 |< COL3 DB6
RD7 |< COL4 DB7
RE0 RS
RE1 W/R
RE2 E
RB5 CS1
RB6 CS2
RB7 RES
R1-R4 10k, +5V, RD0-3
|< - Diode 1N4148
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| Code: |
///////////////////////////////////////////////////////////////////////////
//// KBD_4X4.c ////
//// ////
//// Keyboard driver V 1.0 ////
//// ////
///////////////////////////////////////////////////////////////////////////
//Keypad connection:
#define row0 PIN_D0
#define row1 PIN_D1
#define row2 PIN_D2
#define row3 PIN_D3
#define col0 PIN_D4
#define col1 PIN_D5
#define col2 PIN_D6
#define col3 PIN_D7
// Keypad layout:
char const KEYS[4][4] =
{{'7','8','9','X'},
{'4','5','6','-'},
{'1','2','3','+'},
{'S','0','C','='}};
short int ALL_ROWS (void)
{
if(input (row0) & input (row1) & input (row2) & input (row3))//All rows' are "1"
return (0);
else
return (1);
}
//******************************************************************************
char kbd_getc()
{
set_tris_d(0x0F);
// output_d(0xFF);
static short int kbd_down;
static char last_key;
static BYTE col;
BYTE kchar;
BYTE row;
kchar='\0';
for (col=0;col<5;++col)
{
switch (col)
{
case 0:
output_low(col0);
output_high(col1);
output_high(col2);
output_high(col3);
break;
case 1:
output_high(col0);
output_low(col1);
output_high(col2);
output_high(col3);
break;
case 2:
output_high(col0);
output_high(col1);
output_low(col2);
output_high(col3);
break;
case 3:
output_high(col0);
output_high(col1);
output_high(col2);
output_low(col3);
break;
case 4:
output_high(col0);
output_high(col1);
output_high(col2);
output_high(col3);
break;
}
delay_us(10);
if(kbd_down)
{
if(!ALL_ROWS())
{
kbd_down=FALSE;
kchar=last_key;
last_key='\0';
}
}
else
{
if(ALL_ROWS())
{
if(!input (row0))
row=0;
else if(!input (row1))
row=1;
else if(!input (row2))
row=2;
else if(!input (row3))
row=3;
last_key=KEYS[row][col];
kbd_down=TRUE;
}
}
}
delay_ms(30);//
return(kchar);
}
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freedom
Joined: 10 Jul 2011
Posts: 54
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| Posted: Tue Dec 02, 2014 12:03 pm |
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Thanks anglab
which GLCD driver did you use?
Would you like to provide me diode polarity in this circuit. |
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anglab
Joined: 27 Sep 2010
Posts: 4
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| Posted: Tue Dec 02, 2014 12:51 pm |
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I use HDM64GS12.c driver.
Connection schematic.
Last edited by anglab on Tue Dec 02, 2014 5:04 pm; edited 1 time in total |
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