WiFi Communication Between Two ESP8266 Based MCU Through the Home Router




Posted in TechnologyArduino

Introduction: WiFi Communication Between Two ESP8266 Based MCU Through the Home Router

Hello Makers!

Some months ago I started to experiment ESP8266 based NodeMCU and Wemos boards. At first I used them (in my previous POI hunter project) as a smarter Arduino, because they have higher clock frequency, more memory and built in "SD card" (SPIFFS).

In my Arduino projects sometimes I had to send messages between two MCUs. I used wired communications (serial, i2C) and wireless (bluetooth, RF transmitter / receiver and nRF24). So there was not question I will face this topic using ESP modules also.

I started to mine the internet for ready samples but I didn't find an easy solution for MCU-MCU WiFi communication. Finally I started from the basics. According to the description of the Arduino WiFi library and the WiFi library for ESP8266 I made what I wanted.

In the next pages I will share the result with you in two versions. At first two bare MCU will demonstrate the bare minimum solution of the TCP communication. After that I will show an easy application using an additional DHT22 sensor and some OLEDs.

Step 1: Bare Minimum, TCP Communication Between Two ESP8266 MCUs

Yo can see any HW you need in the picture. Only two MCUs (and a PC).

Both MCUs connect to your home WiFi router. (Don't forget to put your SSID and password into the code before upload the code.) One of the MCUs will be a server and the other will be the client. The client triggers the communication asking the server and the server will send an answer. Modifying the messages you will be able to send anything between the two modules.

Your router will give IP addresses to your MCUs during the connection. Launching the server you will see its IP address in the lower row of the OLED. You have to put this IP into the client's program, because the client will connect to the server using this address. Running the devices some days later you server will receive different IP address, and you will need to modify the client program again. To avoid this annoying thing give fix IP address to your server.

Things you have to do to launch the server:

  • Connect one MCU to a PC with USB cable.
  • Open the "wifi_server_01.ino".
  • Replace the asterisks "****" with the SSID and the password of your home WiFi router.
  • Open the settings of your home WiFi router and choose a free IP address which is out of the DHCP range.
  • Set the IP of your server (row15).
  • Gateway will be the IP of your WiFi router.
  • Upload the program.
  • Run the serial monitor of the Arduino IDE.

Things you have to do to launch the client(s):

  • Run an additional Arduino IDE.
  • Open the "wifi_client_01.ino".
  • Replace the asterisks "****" with the SSID and the password of your home WiFi router.
  • Put the IP address of your server into the 15th row.
  • Upload the program.
  • Run the serial monitor for the new Arduino IDE also.

The client connects to the server soon and you have to see the received messages in both terminal windows. During the communication the built in LEDs will flash for a short time.

Step 2: DHT Server With Clients

Here is an application which uses the TCP communication between ESP8266 MCUs.

A Wemos server listens, reads the DHT22 and shows the temperature and its own IP address on a small OLED screen. Two NodeMCU clients trigger the server and receives the temperature value as the answer. During the communication the server's OLED switches to inverse.

There is only a small modification in the server's program. After some hour work it sometimes stopped serving the clients. It readed the DHT22 and refreshed the OLED, but clients didn't received any answer. To solve this problem I started a timer. The program resets it after serving a client. If the timer reaches 30000 (30 seconds), the server disconnects from the WiFi network and reconnects again.

According to the attached schematics you can build the server and client hardware. Uploading the programs you will have a remote thermometer. Modifying the programs you can build your own project in which the ESP8266 based MCUs can communicate with each other.

Of course every device connected to your local network will be able to ask the DHT server. You can see a screenshot about my mobile also.



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    2 Questions


    How many ESP8266 devices can be connected to a WiFi router?


    Hi Keyur,
    I do not know. It depends on your router, not on ESPs.

    Does this uses TCP or UDP protocol. Because the ESP8266WiFi library uses only UDP, In which the packets might get lost.


    Hi, I'm using an ESP8166-01 to control an Arduino Mega. I was able to turn on and off an LED with a simple web page, when the computer and the esp8266 are both connected to the same wireless router. However, when I use the webpage on a computer that is not connected to my home router, nothing happens. Can you advise what to do? I think there must be an issue with port forwarding or something. Thanks!


    Hi I want to transfer data by connecting Nodemakers. One accees point, connect to it on the other and I want to see this data on the computer screen Can I do this with the codes you share ? help mee please

    4 replies

    Hi PeldaD,

    I am sorry I don't understand well your question. If you would like to make an accesspoint-station communication then my other instructable will be better for you: https://www.instructables.com/id/Accesspoint-Station-Communication-Between-Two-ESP8/#CGDQ2RAJ6IFA8P1


    I want to communicate data between multiple ESPs. Can I do it with these codes? How can I change these codes according to my program? can you speak Turkish ?

    能用Use English communication is very good, I also hope that we use is Chinese. Your problem solved?

    Yes. This code sends data from the client to the server and the server answers it.

    Both program contains comments, which explain the work of the code. Reading this comments you will find the program lines which sends a message and the other which receives.

    No, I am sorry, I don't speak Turkish.

    hello sir pls help me

    I am loaded above code into my two MCUs

    but i have doubt in server programe that is "

    Open the settings of your home WiFi router and choose a free IP address which is out of the DHCP range


    IPAddress gateway(192,168,1,1); // gateway of your network

    my client is working but server dnt..

    1 reply

    Hi vinutp1989,
    there may be a conflict between the DHCP settings of your router and and the fix IP request of the server.
    There are two ways to solve this conflict.
    1, Set an IP range in your router in which DHCP can give IPs for the DHCP clients. The IP of your server (which is defined in this line: IPAddress ip(192, 168, 0, 80);), has to be outside of this range.
    2, Let DHCP to give IP to your server. To do this you have to comment this line: WiFi.config(ip, gateway, subnet);. This way let the server program to print the current IP address to the serial monitor by running this line: Serial.println(WiFi.localIP()); in the setup part of the server program.
    After that in the client program you have to replace this IP: IPAddress server(192,168,0,80); with the current IP of your server.

    Hello Gyalu,

    my application is bit similar to your project.

    My project is to communicate with 2 esp8266 (connected with arduino and relay each) thrugh the app via Home wifi router.

    Can you help in this?

    1 reply

    Hi Shayan,
    I am not an expert, I am hobbyist as you, but can we try. Do you have a concrete question / problem?

    How to set the IP for the server module. You mean its local IP. And is there a possibility of establishing a communication between two ESP modules without internet connection.

    7 replies


    1, you can find the answer in the attached program:

    WiFiServer server(80); // launches the server

    IPAddress ip(192, 168, 0, 80); // fix IP of the server

    IPAddress gateway(192,168,0,1); // WiFi router's IP

    IPAddress subnet(255,255,255,0);

    So the server's IP address will be:

    2, Yes, two ESPs can communicate with each other without internet connection. One has to an access point, the other has to be a client. See the links below.

    I am a beginner so kindly elaborate me on obtaining IP address of the server. How do I ascertain IP address of the module as Is that a local IP.

    My other doubt : Will there be an ssid for the wifi module? Can I use this wifi module like a NRF to transmit and receive data?

    Thanks in advance.


    here is a sample ino, which prints out the local IP of your module to the serial monitor. https://www.arduino.cc/en/Reference/WiFiConfig

    Try to understand the program, make small modifications according the instructions and check the results.

    Hi Gyalu1 ,

    Is there a possibility to send integers instead of strings between two WIFI modules?

    My be, but I never tried.

    I converted the values to string because I always wanted to send more than one numbers in one message.


    see: https://www.instructables.com/id/Accesspoint-Station-Communication-Between-Two-ESP8/

    Hi Gyalu1,
    That was very helpful. Thank you!


    Is it possible to echange data between 2 esp ( one in access point and one in station mode ).

    I tryed to change you're code but i don't arrrived to make it work.

    I arrived to make it work with the 2 esp on my box

    Thanks you