wdt_external_pcf

#include "PCF8574.h"
PCF8574 pcf8574(0x20);
byte pinWDT = P7;
byte pinLED = P4;

byte pinRel[] = {P0, P1, P2, P3};

bool stateWDT = 0;
byte dry[] = {35, 34, 39, 36};
unsigned cur_time_wdt, old_time_wdt;


void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);

  Serial.println("init pcf: ");

  for (int i = 0; i < sizeof(pinRel); i++) {
    Serial.print(pinRel[i]);
    pinMode(pinRel[i], OUTPUT);
  }

  pcf8574.pinMode(pinWDT, OUTPUT);
  pcf8574.pinMode(pinLED, OUTPUT);

  if (pcf8574.begin()) {
    Serial.println("OK");
  } else {
    Serial.println("KO");
  }
  delay(100);
  for (int i = 0; i < sizeof(pinRel); i++) {
    pcf8574.digitalWrite(pinRel[i], HIGH); // SET RELAY OFF
  }
}

void loop() {
  // put your main code here, to run repeatedly:
  cur_time_wdt = millis();
  if (cur_time_wdt - old_time_wdt >= 500) {
    seed_wdt();
    for (int i = 0; i < sizeof(dry); i++) {
      Serial.print(digitalRead(dry[i]));
      Serial.print(",");
    }
    Serial.println();
    old_time_wdt = millis();
  }
}

void seed_wdt() {
  stateWDT = !stateWDT;
  pcf8574.digitalWrite(P7, stateWDT);
  pcf8574.digitalWrite(P4, stateWDT);
}