Communication between two ESP32
This tutorial instructs you how to create connection between two ESP32 via TCP/IP over Ethernet/WiFi and exchange data
Hardware Used In This Tutorial
|2||×||ESP-WROOM-32 Dev Module|
|2||×||Micro USB Cable|
|1||×||(Optional) 5V Power Adapter|
|1||×||(Optional) DC Power Jack|
|1||×||(Optional) ESP32 Screw Terminal Adapter|
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:
|UART (TTL)||very short|
※ NOTE THAT:
- If we connect both ESP32 to the Internet, the communication distance is unlimited
- If we does not connect both ESP32 to the Internet, but we connect them to the same LAN network, the communication distance is restricted within the LAN network.
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)
※ NOTE THAT:
- It does NOT matter if:
- Both of ESP32 uses WiFi
- Both of ESP32 uses Ethernet
- One ESP32 uses Ethernet, the other use WiFi
- UDP protocol is beyond the scope of this tutorial.
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)
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
- ESP32 - LED tutorial
- ESP32 - Button tutorial
- 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
- 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
- Serial Monitor of ESP32 #2
- (**): 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
※ 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 Code for ESP32 #1
ESP32 Code for ESP32 #2
※ NOTE THAT:
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How to connect two ESP32 via Internet
See How to connect two devices via Internet
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