RelayTest with PCF8574

#include <Wire.h>

//  Address of PCF8574
#define DEVICE_1 B0100000

byte Relay = 0;

//  Write a byte to the IO expander
void IOexpanderWrite(byte address, byte _data ) {
  Wire.beginTransmission(address);
  Wire.write(_data);
  Wire.endTransmission();
}

void setup() {
  Serial.begin(115200);
  Wire.begin(D4, D3);/* join i2c bus with SDA=D4 and SCL=D3 of NodeMCU */
}

/*
 * Instead of an integer value you could use a byte.
 * With the byte you can easily set/clear every relay.
 * You can use
 * bitSet(ByteVariable, BitToSet);
 * bitClear(ByteVariable, BitToClear);
 */

void loop() {
  while(i<255) {                  // count up
    Serial.println(i);            // for debug
    IOexpanderWrite(DEVICE_1, i); // send data to PCF
    i++;                          // increase count value
    delay(100);                   // a little delay
  }

  while(i>1) {                    // count down
    Serial.println(i);            // for debug
    IOexpanderWrite(DEVICE_1, i); // send data to PCF
    i--;                          // decrease count value
    delay(100);                   // a little delay
  }
}