Add source and examples

examples/MqttClient/MqttClient.ino

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+/**************************************************************
+ *
+ * For this example, you need to install PubSubClient library:
+ *   https://github.com/knolleary/pubsubclient/releases/latest
+ *
+ * TinyGSM Getting Started guide:
+ *   http://tiny.cc/tiny-gsm-readme
+ *
+ **************************************************************
+ * Use Mosquitto client tools to work with MQTT
+ *   Ubuntu/Linux: sudo apt-get install mosquitto-clients
+ *   Windows:      https://mosquitto.org/download/
+ *
+ * Subscribe for messages:
+ *   mosquitto_sub -h test.mosquitto.org -t GsmClientTest/init -t GsmClientTest/ledStatus -q 1
+ * Toggle led:
+ *   mosquitto_pub -h test.mosquitto.org -t GsmClientTest/led -q 1 -m "toggle"
+ *
+ * You can use Node-RED for wiring together MQTT-enabled devices
+ *   https://nodered.org/
+ * Also, take a look at these additional Node-RED modules:
+ *   node-red-contrib-blynk-websockets
+ *   node-red-dashboard
+ *
+ **************************************************************/
+
+#include <TinyGsmClient.h>
+#include <PubSubClient.h>
+
+// Your GPRS credentials
+// Leave empty, if missing user or pass
+char apn[]  = "YourAPN";
+char user[] = "";
+char pass[] = "";
+
+// Use Hardware Serial on Mega, Leonardo, Micro
+#define GsmSerial Serial1
+
+// or Software Serial on Uno, Nano
+//#include <SoftwareSerial.h>
+//SoftwareSerial GsmSerial(2, 3); // RX, TX
+
+TinyGsmClient gsm(GsmSerial);
+PubSubClient mqtt(gsm);
+
+const char* broker = "test.mosquitto.org";
+
+const char* topicLed = "GsmClientTest/led";
+const char* topicInit = "GsmClientTest/init";
+const char* topicLedStatus = "GsmClientTest/ledStatus";
+
+#define LED_PIN 13
+int ledStatus = LOW;
+
+long lastReconnectAttempt = 0;
+
+void setup() {
+  pinMode(LED_PIN, OUTPUT);
+
+  // Set console baud rate
+  Serial.begin(115200);
+  delay(10);
+
+  // Set GSM module baud rate
+  GsmSerial.begin(115200);
+  delay(3000);
+
+  // Restart takes quite some time
+  // You can skip it in many cases
+  Serial.println("Restarting modem...");
+  gsm.restart();
+
+  Serial.print("Connecting to ");
+  Serial.print(apn);
+  if (!gsm.networkConnect(apn, user, pass)) {
+    Serial.println(" failed");
+    while (true);
+  }
+  Serial.println(" OK");
+
+  // MQTT Broker setup
+  mqtt.setServer(broker, 1883);
+  mqtt.setCallback(mqttCallback);
+}
+
+boolean mqttConnect() {
+  Serial.print("Connecting to ");
+  Serial.print(broker);
+  if (!mqtt.connect("GsmClientTest")) {
+    Serial.println(" failed");
+    return false;
+  }
+  Serial.println(" OK");
+  mqtt.publish(topicInit, "GsmClientTest started");
+  mqtt.subscribe(topicLed);
+  return mqtt.connected();
+}
+
+void loop() {
+
+  if (mqtt.connected()) {
+    mqtt.loop();
+  } else {
+    // Reconnect every 10 seconds
+    unsigned long t = millis();
+    if (t - lastReconnectAttempt > 10000L) {
+      lastReconnectAttempt = t;
+      if (mqttConnect()) {
+        lastReconnectAttempt = 0;
+      }
+    }
+  }
+
+}
+
+void mqttCallback(char* topic, byte* payload, unsigned int len) {
+  Serial.print("Message arrived [");
+  Serial.print(topic);
+  Serial.print("]: ");
+  Serial.write(payload, len);
+  Serial.println();
+
+  // Only proceed if incoming message's topic matches
+  if (String(topic) == topicLed) {
+    ledStatus = !ledStatus;
+    digitalWrite(LED_PIN, ledStatus);
+    mqtt.publish(topicLedStatus, ledStatus ? "1" : "0");
+  }
+}
+