Added source code and schematic.

src/relais.cpp

@@ -0,0 +1,169 @@
+#include <ESP8266WiFi.h>
+#include <PubSubClient.h>
+
+// Name and password of the WLAN access point.
+#define SSID "YourWiFiSSIDhere" // Carmageddon
+#define PASSWORD "OhAndYourWiFiPasswordHere;-)"
+
+#define MQTT_BROKER "192.168.0.25"
+#define MQTT_PORT 1883
+
+// Relais status flag
+uint8_t relais_status = 0;
+
+// Variable for the MQTT Topic where the on/off command arrvies
+char mqtt_topic[64];
+// Variable for the MQTT topic where the current relais state is published to
+char mqtt_topic_state[64];
+
+WiFiClient espClient;
+PubSubClient mqtt(espClient);
+
+void Serialprint(const char *input...) {
+    va_list args;
+    va_start(args, input);
+    for (const char *i = input; *i != 0; ++i) {
+        if (*i != '%') {
+            Serial.print(*i);
+            continue;
+        }
+        switch (*(++i)) {
+            case '%':
+                Serial.print('%');
+                break;
+            case 's':
+                Serial.print(va_arg(args, char*));
+                break;
+            case 'd':
+                Serial.print(va_arg(args, int), DEC);
+                break;
+            case 'b':
+                Serial.print(va_arg(args, int), BIN);
+                break;
+            case 'o':
+                Serial.print(va_arg(args, int), OCT);
+                break;
+            case 'x':
+                Serial.print(va_arg(args, int), HEX);
+                break;
+            case 'f':
+                Serial.print(va_arg(args, double), 2);
+                break;
+        }
+    }
+    va_end(args);
+}
+
+void publish_relais_state() {
+    char payload[7];
+    if(relais_status==0) {
+        sprintf(payload,"%s","off");
+    } else {
+        sprintf(payload,"%s","on");
+    }
+    mqtt.publish(mqtt_topic_state,(byte*) payload,strlen(payload),true);
+    //mqtt.publish(mqtt_topic,payload,NULL,true);
+}
+
+void onWiFiEvent(WiFiEvent_t event) {
+    switch (event) {
+        case WIFI_EVENT_STAMODE_CONNECTED:
+            Serial.println("WiFi connection established.");
+            break;
+        case WIFI_EVENT_STAMODE_DISCONNECTED:
+            Serial.println("WiFi disconnected.");
+            break;
+        case WIFI_EVENT_STAMODE_GOT_IP:
+            Serialprint("WiFi IP recieved: %s\r\n", WiFi.localIP().toString().c_str());
+            break;
+        case WIFI_EVENT_STAMODE_DHCP_TIMEOUT:
+            Serial.println("WiFi DHCP timeout.");
+            break;
+        default:
+            break;
+    }
+}
+
+/**
+ * This callback is registered an run when data for a subscribed topic arrives.
+ * In this case, the payload can only be "on" and "off" which switches the relais
+ * to the corresponding state.
+ * (Maybe this can be tuned a bit: directly use payload by casting it from byte to char.)
+ */
+void mqtt_data_arrived(char *topic, byte *payload, unsigned int length) {
+    char buf[32];
+    snprintf(buf, length + 1, "%s", payload);
+    Serial.println(buf);
+    if (strcmp(buf, "on") == 0) {
+        // LOW (0V) level for "ON", because schematic inverts the signal
+        digitalWrite(2,LOW);
+        relais_status=1;
+        publish_relais_state();
+    } else if (strcmp(buf, "off") == 0) {
+        // HIGH (3,3V) level for "OFF", because schematic inverts the signal
+        digitalWrite(2,HIGH);
+        relais_status=0;
+        publish_relais_state();
+    }
+}
+
+/**
+ * Connect to the MQTT broker if not already connected.
+ * When connecting, register the last will topic, QoS, retained flag and last will also.
+ * This is done to tell any subscriber that the relay is off when it diconnects from the broker.
+ */
+void mqtt_connect() {
+    if (!mqtt.connected()) {
+        //Serialprint("MQTT connecting to: %s\r\n",MQTT_BROKER);
+        if (!mqtt.connect(WiFi.hostname().c_str(), mqtt_topic_state, 0, true, "off")) {
+            // connect using Hostname as Client-ID, last will, will QoS and will retianed flag
+            // Leave the function if the connection could not be established (broker down).
+            return;
+        }
+    }
+    mqtt.subscribe(mqtt_topic);
+}
+
+void setup() {
+    pinMode(2,OUTPUT);
+    digitalWrite(2,HIGH);
+
+
+    // put your setup code here, to run once:
+    Serial.begin(9600);
+
+    WiFi.onEvent(onWiFiEvent, WIFI_EVENT_STAMODE_CONNECTED);
+    WiFi.onEvent(onWiFiEvent, WIFI_EVENT_STAMODE_DISCONNECTED);
+    WiFi.onEvent(onWiFiEvent, WIFI_EVENT_STAMODE_GOT_IP);
+    WiFi.onEvent(onWiFiEvent, WIFI_EVENT_STAMODE_DHCP_TIMEOUT);
+
+    // Connect to Wifi
+    WiFi.mode(WIFI_STA);
+    WiFi.begin(SSID, PASSWORD);
+    if (WiFi.waitForConnectResult(60000) < 0) {
+        ESP.reset();
+    }
+
+    mqtt.setServer(MQTT_BROKER, MQTT_PORT);
+
+    // Set the topic for recieving the commands and the topic for publishing the
+    // relay state (on or off) to the hostname of the ESP (ESP-1A2B3C).
+    sprintf(mqtt_topic, "/%s/relay", WiFi.hostname().c_str());
+    sprintf(mqtt_topic_state, "/%s/relay/state", WiFi.hostname().c_str());
+
+    // Register the MQTT callback function which recieves the data from the topic
+    mqtt.setCallback(mqtt_data_arrived);
+
+    // Now, connect to the MQTT broker.
+    mqtt_connect();
+
+    publish_relais_state();
+}
+
+void loop() {
+    if (!mqtt.loop()) {
+        // loop() returns false if connection was closed
+        // try to reconnect
+        mqtt_connect();
+    }
+}