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4x4 Matrix Membrane Keypad (#27899)
This 16-button keypad provides a useful human interface component for microcontroller projects.
Convenient adhesive backing provides a simple way to mount the keypad in a variety of applications.
Features
Ultra-thin design
Adhesive backing
Excellent price/performance ratio
Easy interface to any microcontroller
Example programs provided for the BASIC
Stamp 2 and Propeller P8X32A
microcontrollers
Key Specifications
Maximum Rating: 24 VDC, 30 mA
Interface: 8-pin access to 4x4 matrix
Operating temperature: 32 to 122 °F
(0 to 50°C)
Dimensions:
Keypad, 2.7 x 3.0 in (6.9 x 7.6 cm)
Cable: 0.78 x 3.5 in (2.0 x 8.8 cm)
Application Ideas
Security systems
Menu selection
Data entry for embedded systems
Copyright © Parallax Inc.
4x4 Matrix Membrane Keypad (#27899)
v1.2 12/16/2011 Page 1 of 5
How it Works
Matrix keypads use a combination of four rows and four columns to provide button states to the host
device, typically a microcontroller. Underneath each key is a pushbutton, with one end connected to one
row, and the other end connected to one column. These connections are shown in Figure 1.
Figure 1: Matrix Keypad Connections
In order for the microcontroller to determine which button is pressed, it first needs to pull each of the
four columns (pins 1-4) either low or high one at a time, and then poll the states of the four rows
(pins 5-8). Depending on the states of the columns, the microcontroller can tell which button is pressed.
For example, say your program pulls all four columns low and then pulls the first row high. It then reads
the input states of each column, and reads pin 1 high. This means that a contact has been made
between column 4 and row 1, so button ‘A’ has been pressed.
Copyright © Parallax Inc.
4x4 Matrix Membrane Keypad (#27899)
v1.2 12/16/2011 Page 2 of 5
Connection Diagrams
Figure 2
For use with the BASIC Stamp
example program listed below.
Figure 3
For use with the Propeller P8X32A
example program listed below.
BASIC Stamp
®
Example Code
The example code below displays the button states of the 4x4 Matrix Membrane Keypad. It uses the
Debug Terminal, which is built into the BASIC Stamp Editor software. The software is a free download
from
www.parallax.com/basicstampsoftware.
' 4x4MatrixKeypad_Demo.bs2
' Display buttons pressed on the 4x4 Matrix Membrane Keypad
' Author: Parallax HK Engineering
' {$STAMP BS2}
' {$PBASIC 2.5}
row
column
keypad
keypadOld
temp
VAR
VAR
VAR
VAR
VAR
Nib
Nib
Word
Word
Nib
'
'
'
'
'
Variable
Variable
Variable
Variable
Variable
space
space
space
space
space
for row counting
for column counting
to store keypad output
to store old keypad output
for polling column states
DEBUG CLS
GOSUB Update
DO
GOSUB ReadKeypad
DEBUG HOME, BIN16 keypad, CR, CR,
BIN4 keypad >> 12,CR,
BIN4 keypad >> 8, CR,
BIN4 keypad >> 4, CR,
BIN4 keypad
' Clear Debug Terminal
' Display keypad graphic
'
'
'
'
'
'
Read keypad button states
Display 16-bit keypad value
Display 1st row 4-bit keypad
Display 2nd row 4-bit keypad
Display 3rd row 4-bit keypad
Display 4th row 4-bit keypad
value
value
value
value
Copyright © Parallax Inc.
4x4 Matrix Membrane Keypad (#27899)
v1.2 12/16/2011 Page 3 of 5
IF keypad <> keypadOld THEN
GOSUB Update
ENDIF
IF keypad THEN
GOSUB display
ENDIF
keypadOld = keypad
LOOP
' If different button is pressed,
' update the keypad graphic to clear
' old display
' Display button pressed in graphic
' Store keypad value in variable keypadOld
' -----[ Subroutine - ReadKeypad ]-------------------------------------------------
' Read keypad button states
ReadKeypad:
keypad = 0
OUTL
= %00000000
' Initialize IO
DIRL
= %00000000
FOR row = 0 TO 3
DIRB = %1111
OUTB = %0000
OUTA = 1 << row
DIRA = 1 << row
temp = 0
FOR column = 0 TO 3
INPUT (column + 4)
temp = temp | (INB & (1 << column))
NEXT
keypad = keypad << 4 | (Temp REV 4)
NEXT
RETURN
' Set columns (P7-P4) as outputs
' Pull columns low (act as pull down)
' Set rows high one by one
' Reset temp variable to 0
' Set columns as inputs
' Poll column state and store in temp
' Store keypad value
' -----[ Subroutine - Update ]-----------------------------------------------------
' Graphical depiction of keypad
Update:
DEBUG CRSRXY,0,7,
"+---+---+---+---+",CR,
"|
|
|
|
|",CR,
"+---+---+---+---+",CR,
"|
|
|
|
|",CR,
"+---+---+---+---+",CR,
"|
|
|
|
|",CR,
"+---+---+---+---+",CR,
"|
|
|
|
|",CR,
"+---+---+---+---+"
RETURN
' -----[ Subroutine - Display ]----------------------------------------------------
' Display button pressed in keypad graphic
Display:
IF KeyPad.BIT15 THEN DEBUG CRSRXY, 02,08,"1"
IF Keypad.BIT14 THEN DEBUG CRSRXY, 06,08,"2"
IF KeyPad.BIT13 THEN DEBUG CRSRXY, 10,08,"3"
IF Keypad.BIT12 THEN DEBUG CRSRXY, 14,08,"A"
IF KeyPad.BIT11 THEN DEBUG CRSRXY, 02,10,"4"
IF Keypad.BIT10 THEN DEBUG CRSRXY, 06,10,"5"
IF KeyPad.BIT9 THEN DEBUG CRSRXY, 10,10,"6"
IF Keypad.BIT8 THEN DEBUG CRSRXY, 14,10,"B"
IF KeyPad.BIT7 THEN DEBUG CRSRXY, 02,12,"7"
IF Keypad.BIT6 THEN DEBUG CRSRXY, 06,12,"8"
IF KeyPad.BIT5 THEN DEBUG CRSRXY, 10,12,"9"
Copyright © Parallax Inc.
4x4 Matrix Membrane Keypad (#27899)
v1.2 12/16/2011 Page 4 of 5
IF Keypad.BIT4
IF KeyPad.BIT3
IF Keypad.BIT2
IF KeyPad.BIT1
IF Keypad.BIT0
RETURN
THEN
THEN
THEN
THEN
THEN
DEBUG
DEBUG
DEBUG
DEBUG
DEBUG
CRSRXY,
CRSRXY,
CRSRXY,
CRSRXY,
CRSRXY,
14,12,"C"
02,14,"*"
06,14,"0"
10,14,"#"
14,14,"D"
Propeller
™
P8X32A Example Code
The example code below displays the button states of the 4x4 Matrix Membrane Keypad, and is a
modified version of the 4x4 Keypad Reader DEMO object by Beau Schwabe.
Note: This application uses the 4x4 Keypad Reader.spin object. It also uses the Parallax Serial Terminal
to display the device output. Both objects and the Parallax Serial Terminal itself are included with the
with the Propeller Tool v1.2.7 or higher, which is available from the Downloads link at
www.parallax.com/Propeller.
{{ 4x4 Keypad Reader PST.spin
Returns the entire 4x4 keypad matrix into a single WORD variable indicating which buttons are
pressed. }}
CON
_clkmode = xtal1 + pll16x
_xinfreq = 5_000_000
OBJ
text : "Parallax Serial Terminal"
KP : "4x4 Keypad Reader"
VAR
word keypad
PUB start
'start term
text.start(115200)
text.str(string(13,"4x4 Keypad Demo..."))
text.position(1, 7)
text.str(string(13,"RAW keypad value 'word'"))
text.position(1, 13)
text.str(string(13,"Note: Try pressing multiple keys"))
repeat
keypad := KP.ReadKeyPad
text.position(5, 2)
text.bin(keypad>>0, 4)
text.position(5,3)
text.bin(keypad>>4, 4)
text.position(5, 4)
text.bin(keypad>>8, 4)
text.position(5, 5)
text.bin(keypad>>12, 4)
text.position(5, 9)
text.bin(keypad, 16)
'<-- One line command to read the 4x4 keypad
'Display 1st ROW
'Display 2nd ROW
'Display 3rd ROW
'Display 4th ROW
'Display RAW keypad value
Revision History
v1.0: original document
v1.1: Updated Figure 1 on page 2
v1.2: Updated Figure 1 on page 2 (again); updated BS2 comments
Copyright © Parallax Inc.
4x4 Matrix Membrane Keypad (#27899)
v1.2 12/16/2011 Page 5 of 5
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