Bridging the wifi networks on nodemcu: how to set the esp8266 as wifi extender, simplest case It seems to me that humidity is getting high in one room in the basement in my house. To monitor the situation temporarily, I would like to build a very small wifi-mesh network to exchange these humidity data to a locally installed raspberry pie server. Most of the time the networking would be in idle state, every some 5 minutes sending the humidity sensor data over mqtt to the server.

What is the simplest code that sets up an esp8266 to connect to an existing wifi network and act as an access point and wifi extender a couple of yards further?

I tried this code:

#include &lt;ESP8266WiFi.h&gt;
#include &lt;ESP8266WebServer.h&gt;

const char* ssid = "SSID_Internet";
const char* password = "qaz12345";

const char* newssid = "SSID_Extender";
const char* newpassword = "qaz12345";

void setup(void){
  Serial.begin(115200);
  Serial.println("");

  // set both access point and station
  WiFi.mode(WIFI_AP_STA);
  WiFi.softAP(newssid, newpassword);

  Serial.print(newssid);
  Serial.print(" server ip: ");
  Serial.println(WiFi.softAPIP());

  WiFi.begin(ssid, password);
  int wifi_it = 0;
  int wifi_status;
  while ((wifi_status = WiFi.status()) != WL_CONNECTED) {
    Serial.println("Trying to connect to wifi");

    wifi_it++;
    delay(500);
  }

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());

  long rssi = WiFi.RSSI();
  Serial.print("Signal strength: ");
  Serial.print(rssi);
  Serial.println("dBm");
}

void loop(void){

}


It successfully registers the esp8266 to the wifi, sets up an AP, but if I connect to SID_Extender with my mobile phone, the internet traffic is not forwarded further.

There are projects that allows to configure multiple esps in user friendly manner, but I am wondering how to setup such an esp myself.
The esp8266 will not bridge the networks. You can perhaps bridge the communication from your other ep8266 on the TCP level with WiFiServer and WiFiClient. Send the sensor value to middle esp8266 running AP and it sends the value to Raspberry.

With MQTT you could create some MQTT proxy. Receive the data with WiFiServer and forward it with WiFiClient. without parsing or anything, only copying the chars between servers client and local client in booth directions

something like this (not tested):

void loop() {

  if (!serverClient || !serverClient.connected()) {
    serverClient = server.available();
  }
  if (!serverClient || !serverClient.connected()) {
    if (client.connected()) {
      client.stop();
    }
    return;
  }

  if (!client || !client.connected()) {
    if (!client.connect(raspiIP, MQTT_PORT)) {
      Serial.println("Can't connect to MQTT");
      delay(1000);
      return;
    }
  }

  while (serverClient.available() &gt; 0) {
    client.write(serverClient.read());
  }
  while (client.available() &gt; 0) {
    serverClient.write(client.read());
  }
}