ESP-NOW with ESP8266: Receive Data from Multiple Boards (many-to-one)

This tutorial shows how to setup an ESP8266 board to receive data from multiple ESP8266 boards via ESP-NOW communication protocol (many-to-one configuration). This configuration is ideal if you want to collect data from several sensors nodes into one ESP8266 board. The boards will be programmed using Arduino IDE.

Other ESP-NOW Guides with the ESP8266:

• Getting Started with ESP-NOW (ESP8266 NodeMCU with Arduino IDE)
• ESP-NOW Two-Way Communication Between ESP8266 Boards
• ESP-NOW with ESP8266: Send Data to Multiple Boards (one-to-many)

Project Overview

This tutorial shows how to setup an ESP8266 board to receive data from multiple ESP8266 boards via ESP-NOW communication protocol (many-to-one configuration) as shown in the following figure.

• One ESP8266 board acts as a receiver/slave;
• Multiple ESP8266 boards act as senders/masters. As an example, we’ll use two senders. You should be able to add more boards to your setup;
• The sender board receives an acknowledge message indicating if the message was successfully delivered or not;
• The ESP8266 receiver board receives the messages from all senders and identifies which board sent the message;
• As an example, we’ll exchange random values between the boards. You should modify this example to send commands or sensor readings.

Note: in the ESP-NOW documentation there isn’t such thing as “sender/master” and “receiver/slave”. Every board can be a sender or receiver. However, to keep things clear we’ll use the terms “sender” and “receiver” or “master” and “slave”.

Prerequisites

We’ll program the ESP8266 boards using Arduino IDE, so before proceeding with this tutorial, make sure you have these boards installed in your Arduino IDE.

• Installing ESP8266 Board in Arduino IDE (Windows, Mac OS X, and Linux)

Getting the Receiver Board MAC Address

To send messages via ESP-NOW, you need to know the receiver board’s MAC address. Each board has a unique MAC address (learn how to Get and Change the ESP8266 MAC Address).

Upload the following code to your ESP8266 receiver board to get is MAC address.

/*
  Rui Santos & Sara Santos - Random Nerd Tutorials
  Complete project details at https://RandomNerdTutorials.com/get-change-esp32-esp8266-mac-address-arduino/
  Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files.  
  The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
*/
#ifdef ESP32
  #include <WiFi.h>
  #include <esp_wifi.h>
#else
  #include <ESP8266WiFi.h>
#endif

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

  Serial.print("ESP Board MAC Address: ");
  #ifdef ESP32
    WiFi.mode(WIFI_STA);
    WiFi.STA.begin();
    uint8_t baseMac[6];
    esp_err_t ret = esp_wifi_get_mac(WIFI_IF_STA, baseMac);
    if (ret == ESP_OK) {
      Serial.printf("%02x:%02x:%02x:%02x:%02x:%02x\n",
                    baseMac[0], baseMac[1], baseMac[2],
                    baseMac[3], baseMac[4], baseMac[5]);
    } else {
      Serial.println("Failed to read MAC address");
    }
  #else
    Serial.println(WiFi.macAddress());
  #endif
}
 
void loop(){

}

View raw code

After uploading the code, press the RST/EN button, and the MAC address should be displayed on the Serial Monitor.

ESP8266 NodeMCU Sender Code (ESP-NOW)

The receiver can identify each sender by its unique MAC address. However, dealing with different MAC addresses on the Receiver side to identify which board sent which message can be a little tricky.

So, to make things easier, we’ll identify each board with a unique number (id) that starts at 1. If you have three boards, one will have ID number 1, the other number 2, and finally number 3. The ID will be sent to the receiver alongside the other variables.

As an example, we’ll exchange a structure that contains the board id number and two random numbers x and y as shown in the figure below.

Upload the following code to each of your sender boards. Don’t forget to increment the id number for each sender board.

/*
  Rui Santos
  Complete project details at https://RandomNerdTutorials.com/esp-now-many-to-one-esp8266-nodemcu/
  
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files.
  
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
*/

#include <ESP8266WiFi.h>
#include <espnow.h>

// REPLACE WITH RECEIVER MAC Address
uint8_t broadcastAddress[] = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};

// Set your Board ID (ESP32 Sender #1 = BOARD_ID 1, ESP32 Sender #2 = BOARD_ID 2, etc)
#define BOARD_ID 2

// Structure example to send data
// Must match the receiver structure
typedef struct struct_message {
    int id;
    int x;
    int y;
} struct_message;

// Create a struct_message called test to store variables to be sent
struct_message myData;

unsigned long lastTime = 0;
unsigned long timerDelay = 10000;

// Callback when data is sent
void OnDataSent(uint8_t *mac_addr, uint8_t sendStatus) {
  Serial.print("\r\nLast Packet Send Status: ");
  if (sendStatus == 0){
    Serial.println("Delivery success");
  }
  else{
    Serial.println("Delivery fail");
  }
}
 
void setup() {
  // Init Serial Monitor
  Serial.begin(115200);
 
  // Set device as a Wi-Fi Station
  WiFi.mode(WIFI_STA);
  WiFi.disconnect();

  // Init ESP-NOW
  if (esp_now_init() != 0) {
    Serial.println("Error initializing ESP-NOW");
    return;
  } 
  // Set ESP-NOW role
  esp_now_set_self_role(ESP_NOW_ROLE_CONTROLLER);

  // Once ESPNow is successfully init, we will register for Send CB to
  // get the status of Trasnmitted packet
  esp_now_register_send_cb(OnDataSent);
  
  // Register peer
  esp_now_add_peer(broadcastAddress, ESP_NOW_ROLE_SLAVE, 1, NULL, 0);

}
 
void loop() {
  if ((millis() - lastTime) > timerDelay) {
    // Set values to send
    myData.id = BOARD_ID;
    myData.x = random(1, 50);
    myData.y = random(1, 50);

    // Send message via ESP-NOW
    esp_now_send(0, (uint8_t *) &myData, sizeof(myData));
    lastTime = millis();
  }
}

View raw code

How the Code Works

Include the ESP8266WiFi and espnow libraries.

#include <ESP8266WiFi.h>
#include <espnow.h>

Insert the receiver’s MAC address on the following line.

uint8_t broadcastAddress[] = {0x5C, 0xCF, 0x7F, 0x99, 0xA1, 0x70};

Set the board ID on the BOARD_ID variable. Don’t forget to change this variable for each of your sender boards.

// Set your Board ID (ESP8266 Sender #1 = BOARD_ID 1, ESP8266 Sender #2 = BOARD_ID 2, etc)
#define BOARD_ID 2

Then, create a structure that contains the data we want to send. We called this structure struct_message and it contains three integer variables: the board id, x and y. You can change this to send whatever variable types you want (but don’t forget to change that on the receiver side too).

typedef struct struct_message {
    int id;
    int x;
    int y;
} struct_message;

Create a new variable of type struct_message that is called myData that will store the variables values.

struct_message myData;

OnDataSent() callback function

Next, define the OnDataSent() function. This is a callback function that will be executed when a message is sent. In this case, this function prints if the message was successfully delivered or not.

void OnDataSent(uint8_t *mac_addr, uint8_t sendStatus) {
  Serial.print("\r\nLast Packet Send Status: ");
  if (sendStatus == 0){
    Serial.println("Delivery success");
  }
  else{
    Serial.println("Delivery fail");
  }
}

setup()

In the setup(), initialize the serial monitor for debugging purposes:

Serial.begin(115200);

Set the device as a Wi-Fi station and disconnect Wi-Fi:

WiFi.mode(WIFI_STA);
WiFi.disconnect();

Initialize ESP-NOW:

if (esp_now_init() != 0) {
  Serial.println("Error initializing ESP-NOW");
  return;
}

Set the board role. This is a sender board, so we’ll set it to ESP_NOW_ROLE_CONTROLLER.

esp_now_set_self_role(ESP_NOW_ROLE_CONTROLLER);

After successfully initializing ESP-NOW, register the callback function that will be called when a message is sent. In this case, register for the OnDataSent() function created previously.

esp_now_register_send_cb(OnDataSent);

Add peer device

To send data to another board (the receiver), you need to pair it as a peer. The following line registers a new peer.

esp_now_add_peer(broadcastAddress, ESP_NOW_ROLE_SLAVE, 1, NULL, 0);

The esp_now_add_peer() function accepts the following arguments, in this order: mac address, peer role, wi-fi channel, key, and key length.

loop()

In the loop(), we’ll send a message via ESP-NOW every 10 seconds (you can change this delay time in the timerDelay variable).

Assign a value to each variable.

myData.id = BOARD_ID;
myData.x = random(1, 50);
myData.y = random(1, 50);

Don’t forget to change the id for each sender board.

Remember that myData is a structure. Here assign the values that you want to send inside the structure. In this case, we’re just sending the id and random values x and y. In a practical application these should be replaced with commands or sensor readings, for example.

Send ESP-NOW message

Finally, send the message via ESP-NOW.

esp_now_send(0, (uint8_t *) &myData, sizeof(myData));

ESP8266 NodeMCU Receiver Code (ESP-NOW)

Upload the following code to your ESP8266 receiver board. The code is prepared to receive data from two different boards. You can easily modify the code to receive data from a different number of boards.

/*
  Rui Santos
  Complete project details at https://RandomNerdTutorials.com/esp-now-many-to-one-esp8266-nodemcu/
  
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files.
  
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
*/

#include <ESP8266WiFi.h>
#include <espnow.h>

// Structure example to receive data
// Must match the sender structure
typedef struct struct_message {
    int id;
    int x;
    int y;
} struct_message;

// Create a struct_message called myData
struct_message myData;

// Create a structure to hold the readings from each board
struct_message board1;
struct_message board2;

// Create an array with all the structures
struct_message boardsStruct[2] = {board1, board2};

// Callback function that will be executed when data is received
void OnDataRecv(uint8_t * mac_addr, uint8_t *incomingData, uint8_t len) {
  char macStr[18];
  Serial.print("Packet received from: ");
  snprintf(macStr, sizeof(macStr), "%02x:%02x:%02x:%02x:%02x:%02x",
           mac_addr[0], mac_addr[1], mac_addr[2], mac_addr[3], mac_addr[4], mac_addr[5]);
  Serial.println(macStr);
  memcpy(&myData, incomingData, sizeof(myData));
  Serial.printf("Board ID %u: %u bytes\n", myData.id, len);
  // Update the structures with the new incoming data
  boardsStruct[myData.id-1].x = myData.x;
  boardsStruct[myData.id-1].y = myData.y;
  Serial.printf("x value: %d \n", boardsStruct[myData.id-1].x);
  Serial.printf("y value: %d \n", boardsStruct[myData.id-1].y);
  Serial.println();
}
 
void setup() {
  // Initialize Serial Monitor
  Serial.begin(115200);
  
  // Set device as a Wi-Fi Station
  WiFi.mode(WIFI_STA);
  WiFi.disconnect();

  // Init ESP-NOW
  if (esp_now_init() != 0) {
    Serial.println("Error initializing ESP-NOW");
    return;
  }
  
  // Once ESPNow is successfully Init, we will register for recv CB to
  // get recv packer info
  esp_now_set_self_role(ESP_NOW_ROLE_SLAVE);
  esp_now_register_recv_cb(OnDataRecv);
}

void loop(){
  // Access the variables for each board
  /*int board1X = boardsStruct[0].x;
  int board1Y = boardsStruct[0].y;
  int board2X = boardsStruct[1].x;
  int board2Y = boardsStruct[1].y;
  */
}

View raw code

How the Code Works

Similarly to the sender, start by including the libraries:

#include <ESP8266WiFi.h>
#include <espnow.h>

Create a structure to receive the data. This structure should be the same defined in the sender sketch.

typedef struct struct_message {
    int id;
    int x;
    int y;
} struct_message;

Create a struct_message variable called myData that will hold the data received.

struct_message myData;

Then, create a struct_message variable for each board, so that we can assign the received data to the corresponding board. Here we’re creating structures for two sender boards. If you have more sender boards, you need to create more structures.

struct_message board1;
struct_message board2;

Create an array that contains all the board structures. If you’re using a different number of boards you need to change that.

struct_message boardsStruct[2] = {board1, board2};

onDataRecv()

Create a callback function that is called when the ESP8266 receives the data via ESP-NOW. The function is called onDataRecv() and should accept several parameters as follows:

void OnDataRecv(uint8_t * mac_addr, uint8_t *incomingData, uint8_t len) {

Get the sender board’s MAC address:

Serial.print("Packet received from: ");
snprintf(macStr, sizeof(macStr), "%02x:%02x:%02x:%02x:%02x:%02x",
         mac_addr[0], mac_addr[1], mac_addr[2], mac_addr[3], mac_addr[4], mac_addr[5]);
Serial.println(macStr);

Copy the content of the incomingData data variable into the myData variable.

memcpy(&myData, incomingData, sizeof(myData));

Now, the myData structure contains several variables with the values sent by one of the ESP8266 senders. We can identify which board send the packet by its ID: myData.id.

This way, we can assign the values received to the corresponding boards on the boardsStruct array:

boardsStruct[myData.id-1].x = myData.x;
boardsStruct[myData.id-1].y = myData.y;

For example, imagine you receive a packet from board with id 2. The value of myData.id is 2.

So, you want to update the values of the board2 structure. The board2 structure is the element with index 1 on the boardsStruct array. That’s why we subtract 1, because arrays in C have 0 indexing. It may help if you take a look at the following image.

setup()

In the setup(), initialize the Serial Monitor.

Serial.begin(115200);

Set the device as a Wi-Fi Station and disconnect Wi-Fi.

WiFi.mode(WIFI_STA);
WiFi.disconnect();

Initialize ESP-NOW:

if (esp_now_init() != ESP_OK) {
  Serial.println("Error initializing ESP-NOW");
  return;
}

Set the board role. This is a receiver board, so we’ll set it to ESP_NOW_ROLE_SLAVE.

Register for a callback function that will be called when data is received. In this case, we register for the OnDataRecv() function that was created previously.

esp_now_register_recv_cb(OnDataRecv);

The following lines commented on the loop exemplify what you need to do if you want to access the variables of each board structure. For example, to access the x value of board1:

int board1X = boardsStruct[0].x;

Demonstration

Upload the sender code to each of your sender boards. Don’t forget to give a different ID to each board.

Upload the receiver code to the ESP8266 receiver board. Don’t forget to modify the structure to match the number of sender boards.

On the senders’ Serial Monitor, you should get a “Delivery Success” message if the messages are delivered successfully.

On the receiver board, you should be receiving the packets from all the other boards. In this test, we were receiving data from 2 different boards.

Wrapping Up

In this tutorial you’ve learned how setup an ESP8266 to receive data from multiple ESP8266 boards using ESP-NOW (many-to-one configuration). You can do something similar with ESP32 boards (ESP32 ESP-NOW: Many-to-one).

As an example, we’ve exchanged random numbers. In a practical application those should be replaced with actual sensor readings or commands. This is ideal if you want to collect data from several sensor nodes.

We have other tutorials related with ESP-NOW that you may like:

• Getting Started with ESP-NOW (ESP8266 NodeMCU with Arduino IDE)
• ESP-NOW Two-Way Communication Between ESP8266 Boards
• ESP-NOW with ESP8266: Send Data to Multiple Boards (one-to-many)

Learn more about ESP8266 with our resources:

• Home Automation using ESP8266
• MicroPython Programming with ESP32 and ESP8266
• More ESP8266 NodeMCU Projects and Tutorials…

Thanks for reading.