Working MQTT example for a Digistump Oak

oak-mqtt-led.ino

#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <string.h>

// Update with values suitable for your network.
const char* mqtt_server = "pine64";

WiFiClient espClient;
PubSubClient client(espClient);
long lastMsg = 0;
char msg[50];

int value = 0;

const byte ledPin = 1; // Pin with LED on Digistump Oak

long lastReconnectAttempt = 0;

void setup()
{
  pinMode(ledPin, OUTPUT);
  Particle.publish("MQTT ledStatus sketch starting...");

  client.setServer(mqtt_server, 1883);
  client.setCallback(callback);
  lastReconnectAttempt = 0;
}

void callback(char* topic, byte* payload, unsigned int length)
{
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] ");
  for (int i = 0; i < length; i++)
  {
    char receivedChar = (char)payload[i];
    Serial.print(receivedChar);
    if (receivedChar == '0')
      digitalWrite(ledPin, LOW);
    if (receivedChar == '1')
      digitalWrite(ledPin, HIGH);
  }
  Serial.println();
}

boolean reconnect()
{
  if (client.connect("OAK"))
  {
    // Once connected, publish an announcement...
    client.publish("outTopic/stat", "hello world");
    // ... and resubscribe
    client.subscribe("ledStatus");
  }
  return client.connected();
}

void loop()
{
  long now = millis();
  if (!client.connected())
  {
    if (now - lastReconnectAttempt > 5000)
    {
      lastReconnectAttempt = now;
      // Attempt to reconnect
      if (reconnect())
      {
        lastReconnectAttempt = 0;
      }
    }
  }
  else
  {
    client.loop();
  }
  delay(20);
}