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Topic: i2c port expander PCF8574 as input (Read 8590 times) previous topic - next topic


To only get one output each time you change the button state then change the lines:-

attachInterrupt(5, expanderInterrupt, LOW);
attachInterrupt(5, expanderInterrupt, CHANGE);


The pullup resistor was ok i think. In doubt check datasheet. :)

Fig.13  Application of multiple PCF8574s with interrupt.



Yei! I have double checked every connection again and I have ended up with a pair of codes in output what I press my button. I was able to idendify this to change the data on my lcd screen. I have still to semplify my code but more or less is working now. I will post it as soon as possible. The code of Yot was my key in this work, thanks again! Thanks to everyone :)

I am programming this system to sobstitute the lcd clock of my car, to have an enhanced clock and the possibility to switch visual to see the temperature of many electronics I have installed (via i2c) into.

Federico - Sideralis
Arduino &C: http://www.sideralis.org
Foto: http://blackman.amicofigo.com


Can you please post the working code


This is my code, it's working but perhaps not perfect :) Keep in mind that is my code there is also the part of code that is needed by my rtc.

Code: [Select]

#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <WProgram.h>
#include <DS1307.h>

int rtc[7];
byte data[56];
char orario[16]; //non cambiare 16 perchè per qualche motivo non va piu' niente dopo
char dataOdierna[16];
int anno;
int changeScreen = 0;
int k = 0;
int primaAccensione = 0;

#define expander 0x20  // Address with three address pins grounded (B0100000).
                    // Note that the R/W bit is not part of this address.
volatile byte count = 0;

uint8_t bell[8]  = {0x4,0xe,0xe,0xe,0x1f,0x0,0x4};
uint8_t note[8]  = {0x2,0x3,0x2,0xe,0x1e,0xc,0x0};
uint8_t clock[8] = {0x0,0xe,0x15,0x17,0x11,0xe,0x0};
uint8_t heart[8] = {0x0,0xa,0x1f,0x1f,0xe,0x4,0x0};
uint8_t duck[8]  = {0x0,0xc,0x1d,0xf,0xf,0x6,0x0};
uint8_t check[8] = {0x0,0x1,0x3,0x16,0x1c,0x8,0x0};
uint8_t cross[8] = {0x0,0x1b,0xe,0x4,0xe,0x1b,0x0};
uint8_t retarrow[8] = {      0x1,0x1,0x5,0x9,0x1f,0x8,0x4};
LiquidCrystal_I2C lcd(expander,8,2);  // set the LCD address to 0x20 for a 16 chars and 2 line display

void setup()
 attachInterrupt(0, expanderInterrupt, CHANGE);

 lcd.init();        // initialize the lcd
 lcd.noBacklight(); // accende e spegne l'uscita sul pin 12.
                    // lcd.backlight();
                    // sink current +5V------+LED-------330Rresistor------P8574pin
 lcd.createChar(0, bell);
 lcd.createChar(1, note);
 lcd.createChar(2, clock);
 lcd.createChar(3, heart);
 lcd.createChar(4, duck);
 lcd.createChar(5, check);
 lcd.createChar(6, cross);
 lcd.createChar(7, retarrow);
 lcd.print(" System");
 lcd.setCursor(0, 1);
 lcd.print(" Ready.");
 for(int i=0; i<9; i++)  {
 for(int i=0; i<56; i++)  {


void loop()

 /*for(int i=0; i<7; i++)
  Serial.print(" ");

 //rtc[0] --> secondi
 //Tramite questo IF faccio lampeggiare il : per i secondi
 if (rtc[0]%2) {
   sprintf(orario,"%02d:%02d",rtc[2],rtc[1]); //%02d converte 9 in 09 e 32 in 32
 else {
   sprintf(orario,"%02d %02d",rtc[2],rtc[1]);
 if (changeScreen==0) {
   lcd.print(2, BYTE);
 else if (changeScreen==1) {
   lcd.print(1, BYTE);
   lcd.print(4, BYTE);
   lcd.print("hcca XX");
 if (count == 1) {
   count = 0;
   attachInterrupt(0, expanderInterrupt, LOW);
   if (primaAccensione==0) {changeScreen=0; primaAccensione++;}
   else if (k==1) { changeScreen=!changeScreen; lcd.clear(); }
   else if (k>1) { k=0; }

// display all keycodes
void displayKeyCodes(void) {
 uint8_t i = 0;
 while (1) {
   lcd.print("Codes 0x"); lcd.print(i, HEX);
   lcd.print("-0x"); lcd.print(i+8, HEX);
   lcd.setCursor(0, 1);
   for (int j=0; j<8; j++) {
     lcd.print(i+j, BYTE);

// Funzioni per interrupt da arduino
void expanderInterrupt() {    
 count = 1;

void expanderWrite(byte _data ) {

byte expanderRead() {
 byte _data;
 Wire.requestFrom(expander, 1);
 if(Wire.available()) {
   _data = Wire.receive();
 return _data;

Federico - Sideralis
Arduino &C: http://www.sideralis.org
Foto: http://blackman.amicofigo.com

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