Communication between two ESP32

Hardware Used In This Tutorial

Communication between two ESP32 - Overview

There are many ways to make ESP32 #1 communicate with ESP32 #2. Depending on the distance, we can choose one of the below ways:

This tutorial is going to use Ethernet/WiFi for communication between two ESP32.

Communication between two ESP32 via Ethernet/WiFi

Two ESP32 can communicate with each other via Ethernet/WiFi if:

• Two ESP32 in the same LAN network. They does not need to connect to Internet
• Two ESP32 in the different LAN networks. They need to connect to Internet

There are two ways that two ESP32 can communicate to each other.

• Two ESP32 communicate with each other directly: one ESP32 is a TCP client, the other is a TCP server.
• Two ESP32 communicate with each other indirectly via a centralized server (e.g. MQTT server): both ESP32 are TCP clients.

It needs an application protocol that two ESP32 uses to communicate to each other. For example:

• Self-defined protocol over raw TCP (directly)
• Modbus TCP (directly)
• HTTP (directly)
• Telnet (directly)
• SSH (directly)
• MQTT (indirectly via a server)

Example Application

Let's realize the following application: A button/switch connected to ESP32 #1 controls an LED connected to ESP32 #2 via Ethernet/WiFi.

To make it simple, This tutorial will use a self-defined protocol (Defined by us, no standard)

Self-defined Protocol

We define a simple protocol as follows:

• Create a TCP connection between ESP32 #1 and ESP32 #2
• ESP32 #1:
• TCP client: actively makes TCP connection request to ESP32 #2
• If the switch's state is changed to ON, ESP32 #1 sends a byte (command) with value 1 to ESP32 #2.
• If the switch's state is changed to OFF, ESP32 #1 sends a byte (command) with value 0 to ESP32 #2.
• ESP32 #2:
• TCP server: listens to a TCP connection request from ESP32 #1. If there is a TCP request, it accepts and the connection is created.
• If It receives a byte:
• If the value is 1, Turn LED on
• If the value is 0, Turn LED off

Wiring Diagram

https://esp32io.com/images/tutorial/two-esp32-led-switch-button.jpg

※ NOTE THAT:

It needs touse a resistor for LED if it does not have a built-in resistor. We have dedicated tutorials for button and LED. You can learn more about them in:

• ESP32 - LED tutorial
• ESP32 - Button tutorial

ESP32 Code for ESP32 #1


/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/communication-between-two-esp32 */ // ESP32 #1: TCP CLIENT + A BUTTON/SWITCH #include <ezButton.h> #include <SPI.h> #include <Ethernet.h> #define BUTTON_PIN 7 #define SERVER_PORT 4080 ezButton button(BUTTON_PIN); // create ezButton that attach to pin 7; byte mac[] = {0x00, 0xAA, 0xBB, 0xCC, 0xDE, 0x03}; IPAddress serverAddress(192, 168, 0, 180); EthernetClient TCPclient; void setup() { Serial.begin(9600); button.setDebounceTime(50); // set debounce time to 50 milliseconds Serial.println("ESP32 #1: TCP CLIENT + A BUTTON/SWITCH"); // Initialize Ethernet Shield: if (Ethernet.begin(mac) == 0) Serial.println("ESP32 #1: Failed to configure Ethernet using DHCP"); // connect to TCP server (ESP32 #2 ) if (TCPclient.connect(serverAddress, SERVER_PORT)) Serial.println("ESP32 #1: Connected to TCP server"); else Serial.println("ESP32 #1: Failed to connect to TCP server"); } void loop() { button.loop(); // MUST call the loop() function first if (!TCPclient.connected()) { Serial.println("ESP32 #1: Connection is disconnected"); TCPclient.stop(); // reconnect to TCP server (ESP32 #2) if (TCPclient.connect(serverAddress, SERVER_PORT)) Serial.println("ESP32 #1: Reconnected to TCP server"); else Serial.println("ESP32 #1: Failed to reconnect to TCP server"); } if (button.isPressed()) { TCPclient.write('1'); TCPclient.flush(); Serial.println("ESP32 #1: - The button is pressed, sent command: 1"); } if (button.isReleased()) { TCPclient.write('0'); TCPclient.flush(); Serial.println("ESP32 #1: - The button is released, sent command: 0"); } }

ESP32 Code for ESP32 #2


/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/communication-between-two-esp32 */ // ESP32 #2: TCP SERVER + AN LED #include <SPI.h> #include <Ethernet.h> #define LED_PIN 7 #define SERVER_PORT 4080 byte mac[] = {0x00, 0xAA, 0xBB, 0xCC, 0xDE, 0x02}; EthernetServer TCPserver(SERVER_PORT); void setup() { Serial.begin(9600); pinMode(LED_PIN, OUTPUT); Serial.println("ESP32 #2: TCP SERVER + AN LED"); // Initialize Ethernet Shield: if (Ethernet.begin(mac) == 0) Serial.println("ESP32 #2: Failed to configure Ethernet using DHCP"); // Print your local IP address: Serial.print("ESP32 #2: TCP Server IP address: "); Serial.println(Ethernet.localIP()); Serial.println("ESP32 #2: -> Please update the serverAddress in ESP32 #1 code"); // Listening for a TCP client (from ESP32 #1) TCPserver.begin(); } void loop() { // Wait for a TCP client from ESP32 #1: EthernetClient client = TCPserver.available(); if (client) { // Read the command from the TCP client: char command = client.read(); Serial.print("ESP32 #2: - Received command: "); Serial.println(command); if (command == '1') digitalWrite(LED_PIN, HIGH); // Turn LED on else if (command == '0') digitalWrite(LED_PIN, LOW); // Turn LED off Ethernet.maintain(); } }

Quick Instructions

• If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE.
• Wire a button/switch to ESP32 #1
• Wire an LED to ESP32 #2
• Open Arduino IDE (called Arduino IDE #1)
• Install ezButton library on Arduino IDE
• Connect ESP32 #1 to PC via USB cable and select COM port of ESP32 #1 on Arduino IDE #1
• Open another Arduino IDE window (called Arduino IDE #2) by clicking on Arduino IDE icon on your PC (important!^(**))
• Connect ESP32 #2 to PC via USB cable and select COM port of ESP32 #2 on Arduino IDE #2
• Copy ESP32 #1 code, paste to Arduino IDE #1 and save it (named ESP321)
• Copy ESP32 #2 code, paste to Arduino IDE #2 and save it (named ESP322)
• Upload ESP32 #2 code to ESP32 #2 first
• Open Serial Monitor on Arduino IDE #2, get TCP Server IP address
COM6
Send
ESP32 #2: TCP SERVER + AN LED TCP Server IP address: 192.168.0.2 -> Please update the serverAddress in ESP32 #1 code
Autoscroll Show timestamp
Clear output
9600 baud  
Newline  
• Update TCP Server IP address in ESP32 #1 code
• Upload ESP32 #1 code to ESP32 #1
• Open Serial Monitor on Arduino IDE #1
• Press and hold the button on ESP32 #1 → see LED's state on ESP32 #2 (ON)
• Release button on ESP32 #1 → see LED's state on ESP32 #2 (OFF)
• Do the above process several times.
• See output on both Serial Monitors
• Serial Monitor of ESP32 #1
COM6
Send
ESP32 #1: TCP CLIENT + A BUTTON/SWITCH ESP32 #1: Connected to TCP server ESP32 #1: - The button is pressed, sent command: 1 ESP32 #1: - The button is released, sent command: 0 ESP32 #1: - The button is pressed, sent command: 1 ESP32 #1: - The button is released, sent command: 0 ESP32 #1: - The button is pressed, sent command: 1 ESP32 #1: - The button is released, sent command: 0
Autoscroll Show timestamp
Clear output
9600 baud  
Newline  
• Serial Monitor of ESP32 #2
COM6
Send
ESP32 #2: TCP SERVER + AN LED ESP32 #2: TCP Server IP address: 192.168.0.2 ESP32 #2: -> Please update the serverAddress in ESP32 #1 code ESP32 #2: - Received command: 1 ESP32 #2: - Received command: 0 ESP32 #2: - Received command: 1 ESP32 #2: - Received command: 0 ESP32 #2: - Received command: 1 ESP32 #2: - Received command: 0
Autoscroll Show timestamp
Clear output
9600 baud  
Newline  

※ NOTE THAT:

• (**): If you open Arduino IDE #2 window via "File" → "New" or "Open" from Arduino IDE #2 window, you will NOT be able to open two Serial Monitors for two ESP32 in the same PC at the same time.
• There is an alternative to this self-defined protocol. It is the Modbus TCP. The Modbus protocol is standardized, it has many advantages over the self-defined protocol. See more in ESP32 - Modbus tutorial

Video Tutorial

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How to connect two ESP32 via Internet

See How to connect two devices via Internet

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