ESP-NOW is a wireless communication protocoldeveloped 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 PinESP32 PinR1GPIO 19R2GPIO 18R3GPIO 5R4GPIO 17C1GPIO 16C2GPIO 4C3GPIO 22C4GPIO 15

⚙️ Pinout (Example RECEIVER)

Neopixel PinESP32 PinVCCVCCGNGGNDDOUTGPIO15

🧪 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() {

}