ESP32. Two-way communication protocol between two modules.

Code to know the address “MAC” of “Monitor Series”:

#include <Arduino.h>
#include "WiFi.h"

void setup(){
  Serial.begin(9600);
  WiFi.mode(WIFI_STA);
  Serial.println(WiFi.macAddress());
}
void loop(){
  Serial.println(WiFi.macAddress());
  delay(5000);
}

Code from which a module “ESP32” transfers data to another module and simultaneously receives data from the same module:

Modul 1:

#include <esp_now.h>
#include <WiFi.h>

// REPLACE WITH YOUR RECEIVER MAC Address
uint8_t broadcastAddress[] = {0x34, 0x86, 0x5D, 0xFD, 0x3D, 0xca};

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

// Create a struct_message called myData
struct_message myDataRec;
struct_message myDataSen;

esp_now_peer_info_t peerInfo;

// callback when data is sent
void OnDataSent(const uint8_t *mac_addr, esp_now_send_status_t status) {
  Serial.print("\r\nLast Packet Send Status:\t");
  Serial.println(status == ESP_NOW_SEND_SUCCESS ? "Delivery Success" : "Delivery Fail");
}
 
// callback function that will be executed when data is received
void OnDataRecv(const uint8_t * mac, const uint8_t *incomingData, int len) {
  memcpy(&myDataRec, incomingData, sizeof(myDataRec));
  Serial.print("Bytes received: ");
  Serial.println(len);
  Serial.print("Int: ");
  Serial.println(myDataRec.a);
  Serial.println();
}
 
void setup() {
  // Init Serial Monitor
  Serial.begin(9600);
 
  // Set device as a Wi-Fi Station
  WiFi.mode(WIFI_STA);

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

  // 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
  memcpy(peerInfo.peer_addr, broadcastAddress, 6);
  peerInfo.channel = 0;  
  peerInfo.encrypt = false;
  
  // Add peer        
  if (esp_now_add_peer(&peerInfo) != ESP_OK){
    Serial.println("Failed to add peer");
    return;
  }
  // Once ESPNow is successfully Init, we will register for recv CB to
  // get recv packer info
  esp_now_register_recv_cb(OnDataRecv);
}
 
void loop() {
  // Set values to send
  myDataSen.a = 1;

  // Send message via ESP-NOW
  esp_err_t result = esp_now_send(broadcastAddress, (uint8_t *) &myDataSen, sizeof(myDataSen));
   
  if (result == ESP_OK) {
    Serial.println("Sent with success");
  }
  else {
    Serial.println("Error sending the data");
  }
  delay(2000);
}

Modul 2:

#include <esp_now.h>
#include <WiFi.h>

// REPLACE WITH YOUR RECEIVER MAC Address
uint8_t broadcastAddress[] = {0xc0, 0x49, 0xef, 0xce, 0x19, 0x24};

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

// Create a struct_message called myData
struct_message myDataRec;
struct_message myDataSen;

esp_now_peer_info_t peerInfo;

// callback when data is sent
void OnDataSent(const uint8_t *mac_addr, esp_now_send_status_t status) {
  Serial.print("\r\nLast Packet Send Status:\t");
  Serial.println(status == ESP_NOW_SEND_SUCCESS ? "Delivery Success" : "Delivery Fail");
}

// callback function that will be executed when data is received
void OnDataRecv(const uint8_t * mac, const uint8_t *incomingData, int len) {
  memcpy(&myDataRec, incomingData, sizeof(myDataRec));
  Serial.print("Bytes received: ");
  Serial.println(len);
  Serial.print("Int: ");
  Serial.println(myDataRec.a);
  Serial.println();
}
 
void setup() {
  // Initialize Serial Monitor
  Serial.begin(9600);
  
  // Set device as a Wi-Fi Station
  WiFi.mode(WIFI_STA);

  // Init ESP-NOW
  if (esp_now_init() != ESP_OK) {
    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_register_recv_cb(OnDataRecv);

  // 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
  memcpy(peerInfo.peer_addr, broadcastAddress, 6);
  peerInfo.channel = 0;  
  peerInfo.encrypt = false;
  
  // Add peer        
  if (esp_now_add_peer(&peerInfo) != ESP_OK){
    Serial.println("Failed to add peer");
    return;
  }
}
 
void loop() {
  // Set values to send
  myDataSen.a = 2;

  // Send message via ESP-NOW
  esp_err_t result = esp_now_send(broadcastAddress, (uint8_t *) &myDataSen, sizeof(myDataSen));
   
  if (result == ESP_OK) {
    Serial.println("Sent with success");
  }
  else {
    Serial.println("Error sending the data");
  }
  delay(2000);
}

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