4x4 Keypad I2C 8bit IO Expander

PCF8574A - Manual

4x4 8 wire keypad membrane

This is a great example library for use with keypads and in I2C port expander.

Note: With A0, A1 and A2 grounded on this I2C chip the address becomes 0x38.


#include <Keypad_I2C.h>
#include <Keypad.h>
#include <Wire.h>
// A0, A1, A2 all to GND
#define I2CADDR 0x38

const byte ROWS = 4; //four rows
const byte COLS = 4; //four columns
char keys[ROWS][COLS] = {

// Digitran keypad, bit numbers of PCF8574 i/o port
byte rowPins[ROWS] = {0, 1, 2, 3}; //connect to the row pinouts of the keypad
byte colPins[COLS] = {4, 5, 6, 7}; //connect to the column pinouts of the keypad

Keypad_I2C kpd( makeKeymap(keys), rowPins, colPins, ROWS, COLS, I2CADDR, PCF8574 );

void setup(){
  Wire.begin( );
  kpd.begin( makeKeymap(keys) );
  Serial.println( "start" );
void loop(){
  char key = kpd.getKey();
  if (key){

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