I2C connection example

i2c.c

#include <Wire.h>

void setup() {
  Wire.begin();
  Serial.begin(9600);
}

int reading = 0;


void loop() {
  if (Serial.available() > 0) {
    int input = Serial.read();
    Serial.write("read :");
    Serial.write(input);
    Serial.write("\n");
    command(input);
  }
  delay(70);
}

void off(void){
  // 32 = 0x20 --> this is the first address of PCF8574. it should be changed when you changed the chip.
  Wire.beginTransmission(32);
  Wire.write(byte(0x00));
  Wire.endTransmission();
}

void on(void){
  // 32 = 0x20 --> this is the first address of PCF8574. it should be changed when you changed the chip.
  Wire.beginTransmission(32);
  Wire.write(byte(0xFF));
  Wire.endTransmission();
}

void command(int cmd) {
  Wire.beginTransmission(32);
  Wire.write(byte(cmd));
  Wire.endTransmission();
}