ESP-NOW with ESP32

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📌 What is ESP-NOW?

ESP-NOW is a wireless communication protocol developed by Espressif, allowing ESP32 boards to send and receive data directly without Wi-Fi or internet.

🧠 Key Features

📡 Peer-to-peer communication (up to 20 devices)
⚡ Low power and fast (few milliseconds delay)
🔐 Encrypted data transmission
🚫 No Wi-Fi router or internet needed
🔁 Bi-directional communication supported

🔌 Where to Use (Use Cases)

🎮 Wireless joystick controller
🏠 Smart home automation
🚨 Personal safety devices (like Safeguard+)
🌱 Remote environment sensors
🚗 Vehicle-to-vehicle communication
🎓 College projects requiring mesh or local network

🛠️ Components Needed

✅ 2x ESP32 Boards
✅ Micro USB cables
✅ Arduino IDE installed
✅ Sensor/input (e.g., joystick/keypad)
✅ Output (e.g., LED, buzzer, OLED)

📍 How ESP-NOW Works

ESP32 uses its WiFi in STA mode (no router)
One board becomes sender, other is receiver
Data is sent in small packets (struct format)
Boards communicate using each other’s MAC address

⚙️ Pinout (Example for Sender – 4×4 Keypad)

Keypad Pin	ESP32 Pin
R1	GPIO 19
R2	GPIO 18
R3	GPIO 5
R4	GPIO 17
C1	GPIO 16
C2	GPIO 4
C3	GPIO 22
C4	GPIO 15

⚙️ Pinout (Example RECEIVER)

Neopixel Pin	ESP32 Pin
VCC	VCC
GNG	GND
DOUT	GPIO15

🧪 Applications

🔘 Wireless button panel
📦 Inventory scan/tag systems
🔋 Battery-operated remote devices
🔐 Secure, private IoT devices (no cloud dependency)
🎓 Ideal for IEEE & hackathon projects

💡 Code Overview

Sender Side:

Initialize Wi-Fi STA mode
Register peer MAC address
Pack data using struct
Send using esp_now_send()

Receiver Side:

Register receive callback
Decode received struct
Perform action (like LED on, buzzer, Serial print)

📋 Notes

📶 Keep both ESP32 on the same WiFi channel
📍 Use only MAC Address of peer (receiver)
💬 Packet size should be under 250 bytes
🔌 Both must be in WiFi STA mode
🔄 ESP-NOW doesn’t support IP-based networking (no HTTP/MQTT)

HOW TO CHECK 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.
*/
#include <WiFi.h>
#include <esp_wifi.h>

void readMacAddress(){
  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");
  }
}

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

  WiFi.mode(WIFI_STA);
  WiFi.STA.begin();

  Serial.print("[DEFAULT] ESP32 Board MAC Address: ");
  readMacAddress();
}
 
void loop(){

}
 
 
 
 
SENDER ADDRESS CODE
 
 
/*
  Rui Santos & Sara Santos - Random Nerd Tutorials
  Modified by Akash for keypad input + ESP-NOW
*/

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

// Define rows and columns
const byte ROWS = 4;
const byte COLS = 4;

// Define the key map
char keys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};

// Connect keypad ROW0, ROW1, ROW2 and ROW3 to these ESP32 pins
byte rowPins[ROWS] = {19, 18, 5, 17};

// Connect COL0, COL1, COL2, COL3 to these ESP32 pins
byte colPins[COLS] = {16, 4, 22, 15};

// Create keypad object
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

// Replace with receiver MAC Address
uint8_t broadcastAddress[] = {0x30, 0xC6, 0xF7, 0x22, 0xEB, 0xD8};

// Define message structure
typedef struct struct_message {
  char a[32];  // String data to send
} struct_message;

struct_message myData;
esp_now_peer_info_t peerInfo;

String inputBuffer = "";  // Buffer to store key inputs

// Callback function on successful/failed send
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");
}

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

  // Set device as a Wi-Fi Station
  WiFi.mode(WIFI_STA);
  Serial.print("Sender MAC Address: ");
  Serial.println(WiFi.macAddress());

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

  // Register send callback
  esp_now_register_send_cb(OnDataSent);

  // Register peer
  memset(&peerInfo, 0, sizeof(peerInfo));
  memcpy(peerInfo.peer_addr, broadcastAddress, 6);
  peerInfo.channel = 0;
  peerInfo.encrypt = false;
  peerInfo.ifidx = WIFI_IF_STA;

  if (esp_now_add_peer(&peerInfo) != ESP_OK) {
    Serial.println("Failed to add peer");
    return;
  }

  Serial.println("ESP-NOW Sender Ready");
}

void loop() {
  char key = keypad.getKey();

  if (key) {
    Serial.print("Key Pressed: ");
    Serial.println(key);

    if (key == '#') {
      // Send data only when '#' is pressed
      if (inputBuffer.length() > 0) {
        inputBuffer.toCharArray(myData.a, sizeof(myData.a));
        esp_err_t result = esp_now_send(broadcastAddress, (uint8_t *)&myData, sizeof(myData));
       
        if (result == ESP_OK) {
          Serial.print("Sent: ");
          Serial.println(myData.a);
        } else {
          Serial.println("Error sending the data");
        }
        inputBuffer = "";  // Clear buffer after sending
      }
    } else if (key == '*') {
      // Clear buffer manually using '*'
      inputBuffer = "";
      Serial.println("Buffer cleared");
    } else {
      // Append key to input
      inputBuffer += key;
    }

    delay(300);  // Debounce delay
  }
}
 
 
RECEIVER SIDE CODE
 
 
/*
  Rui Santos & Sara Santos - Random Nerd Tutorials
  Complete project details at https://RandomNerdTutorials.com/esp-now-esp32-arduino-ide/  
  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 <esp_now.h>
#include <WiFi.h>
#include <Adafruit_NeoPixel.h>

#define PIN_NEO_PIXEL 15    // Pin connected to the NeoPixel
#define NUM_PIXELS 4       // Total number of NeoPixels

Adafruit_NeoPixel NeoPixel(NUM_PIXELS, PIN_NEO_PIXEL, NEO_GRB + NEO_KHZ800);

// Structure example to receive data
// Must match the sender structure
typedef struct struct_message {
    char a[32];
   
} struct_message;

// Create a struct_message called myData
struct_message myData;

// callback function that will be executed when data is received
void OnDataRecv(const uint8_t * mac, const uint8_t *incomingData, int len) {
  memcpy(&myData, incomingData, sizeof(myData));
  Serial.print("Bytes received: ");
  Serial.println(len);
  Serial.print("Char: ");
  Serial.println(myData.a);
 
  if(strcmp(myData.a, "1") == 0)
  {
   
      NeoPixel.clear();       // Clear any previous data
      NeoPixel.show();
      NeoPixel.setPixelColor(1, NeoPixel.Color(255, 0, 0));
      NeoPixel.show();
      delay(500);
 
 
  }

  if(strcmp(myData.a, "2") == 0)
  {
      NeoPixel.clear();       // Clear any previous data
      NeoPixel.show();
      NeoPixel.setPixelColor(2, NeoPixel.Color(0,255, 0));
      NeoPixel.show();
      delay(500);
  }
 
  if(strcmp(myData.a, "3") == 0)
  {
   NeoPixel.clear();       // Clear any previous data
   NeoPixel.show();
   NeoPixel.setPixelColor(3, NeoPixel.Color(0, 0, 255));
   NeoPixel.show();
  }
   if(strcmp(myData.a, "23") == 0)
  {
   NeoPixel.clear();       // Clear any previous data
   NeoPixel.show();
   NeoPixel.setPixelColor(3, NeoPixel.Color(0, 255, 255));
   NeoPixel.show();
  }
  if(strcmp(myData.a, "4") == 0)
  {
   NeoPixel.clear();       // Clear any previous data
   NeoPixel.show();
  }

}
 
void setup() {

  NeoPixel.begin();       // Initialize the NeoPixel
  NeoPixel.clear();       // Clear any previous data
  NeoPixel.show();        // Apply the clear
  // Initialize Serial Monitor
  Serial.begin(115200);
 
  // 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(esp_now_recv_cb_t(OnDataRecv));
}
 
void loop() {

 

}

HOW TO CHECK 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.
*/
#include <WiFi.h>
#include <esp_wifi.h>

void readMacAddress(){
  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");
  }
}

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

  WiFi.mode(WIFI_STA);
  WiFi.STA.begin();

  Serial.print("[DEFAULT] ESP32 Board MAC Address: ");
  readMacAddress();
}
 
void loop(){

}
 
 
 
 
SENDER ADDRESS CODE
 
 
/*
  Rui Santos & Sara Santos - Random Nerd Tutorials
  Modified by Akash for keypad input + ESP-NOW
*/

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

// Define rows and columns
const byte ROWS = 4;
const byte COLS = 4;

// Define the key map
char keys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};

// Connect keypad ROW0, ROW1, ROW2 and ROW3 to these ESP32 pins
byte rowPins[ROWS] = {19, 18, 5, 17};

// Connect COL0, COL1, COL2, COL3 to these ESP32 pins
byte colPins[COLS] = {16, 4, 22, 15};

// Create keypad object
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

// Replace with receiver MAC Address
uint8_t broadcastAddress[] = {0x30, 0xC6, 0xF7, 0x22, 0xEB, 0xD8};

// Define message structure
typedef struct struct_message {
  char a[32];  // String data to send
} struct_message;

struct_message myData;
esp_now_peer_info_t peerInfo;

String inputBuffer = "";  // Buffer to store key inputs

// Callback function on successful/failed send
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");
}

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

  // Set device as a Wi-Fi Station
  WiFi.mode(WIFI_STA);
  Serial.print("Sender MAC Address: ");
  Serial.println(WiFi.macAddress());

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

  // Register send callback
  esp_now_register_send_cb(OnDataSent);

  // Register peer
  memset(&peerInfo, 0, sizeof(peerInfo));
  memcpy(peerInfo.peer_addr, broadcastAddress, 6);
  peerInfo.channel = 0;
  peerInfo.encrypt = false;
  peerInfo.ifidx = WIFI_IF_STA;

  if (esp_now_add_peer(&peerInfo) != ESP_OK) {
    Serial.println("Failed to add peer");
    return;
  }

  Serial.println("ESP-NOW Sender Ready");
}

void loop() {
  char key = keypad.getKey();

  if (key) {
    Serial.print("Key Pressed: ");
    Serial.println(key);

    if (key == '#') {
      // Send data only when '#' is pressed
      if (inputBuffer.length() > 0) {
        inputBuffer.toCharArray(myData.a, sizeof(myData.a));
        esp_err_t result = esp_now_send(broadcastAddress, (uint8_t *)&myData, sizeof(myData));
       
        if (result == ESP_OK) {
          Serial.print("Sent: ");
          Serial.println(myData.a);
        } else {
          Serial.println("Error sending the data");
        }
        inputBuffer = "";  // Clear buffer after sending
      }
    } else if (key == '*') {
      // Clear buffer manually using '*'
      inputBuffer = "";
      Serial.println("Buffer cleared");
    } else {
      // Append key to input
      inputBuffer += key;
    }

    delay(300);  // Debounce delay
  }
}
 
 
RECEIVER SIDE CODE
 
 
/*
  Rui Santos & Sara Santos - Random Nerd Tutorials
  Complete project details at https://RandomNerdTutorials.com/esp-now-esp32-arduino-ide/  
  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 <esp_now.h>
#include <WiFi.h>
#include <Adafruit_NeoPixel.h>

#define PIN_NEO_PIXEL 15    // Pin connected to the NeoPixel
#define NUM_PIXELS 4       // Total number of NeoPixels

Adafruit_NeoPixel NeoPixel(NUM_PIXELS, PIN_NEO_PIXEL, NEO_GRB + NEO_KHZ800);

// Structure example to receive data
// Must match the sender structure
typedef struct struct_message {
    char a[32];
   
} struct_message;

// Create a struct_message called myData
struct_message myData;

// callback function that will be executed when data is received
void OnDataRecv(const uint8_t * mac, const uint8_t *incomingData, int len) {
  memcpy(&myData, incomingData, sizeof(myData));
  Serial.print("Bytes received: ");
  Serial.println(len);
  Serial.print("Char: ");
  Serial.println(myData.a);
 
  if(strcmp(myData.a, "1") == 0)
  {
   
      NeoPixel.clear();       // Clear any previous data
      NeoPixel.show();
      NeoPixel.setPixelColor(1, NeoPixel.Color(255, 0, 0));
      NeoPixel.show();
      delay(500);
 
 
  }

  if(strcmp(myData.a, "2") == 0)
  {
      NeoPixel.clear();       // Clear any previous data
      NeoPixel.show();
      NeoPixel.setPixelColor(2, NeoPixel.Color(0,255, 0));
      NeoPixel.show();
      delay(500);
  }
 
  if(strcmp(myData.a, "3") == 0)
  {
   NeoPixel.clear();       // Clear any previous data
   NeoPixel.show();
   NeoPixel.setPixelColor(3, NeoPixel.Color(0, 0, 255));
   NeoPixel.show();
  }
   if(strcmp(myData.a, "23") == 0)
  {
   NeoPixel.clear();       // Clear any previous data
   NeoPixel.show();
   NeoPixel.setPixelColor(3, NeoPixel.Color(0, 255, 255));
   NeoPixel.show();
  }
  if(strcmp(myData.a, "4") == 0)
  {
   NeoPixel.clear();       // Clear any previous data
   NeoPixel.show();
  }

}
 
void setup() {

  NeoPixel.begin();       // Initialize the NeoPixel
  NeoPixel.clear();       // Clear any previous data
  NeoPixel.show();        // Apply the clear
  // Initialize Serial Monitor
  Serial.begin(115200);
 
  // 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(esp_now_recv_cb_t(OnDataRecv));
}
 
void loop() {

 

}

ESP-NOW with ESP32

📌 What is ESP-NOW?

🧠 Key Features

🔌 Where to Use (Use Cases)

🛠️ Components Needed

📍 How ESP-NOW Works

⚙️ Pinout (Example for Sender – 4×4 Keypad)

⚙️ Pinout (Example RECEIVER)

🧪 Applications

💡 Code Overview

Sender Side:

Receiver Side:

📋 Notes

Author

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ESP-NOW with ESP32

📌 What is ESP-NOW?

🧠 Key Features

🔌 Where to Use (Use Cases)

🛠️ Components Needed

📍 How ESP-NOW Works

⚙️ Pinout (Example for Sender – 4×4 Keypad)

⚙️ Pinout (Example RECEIVER)

🧪 Applications

💡 Code Overview

Sender Side:

Receiver Side:

📋 Notes

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Author

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