12Dec
ESP-NOW with ESP32
What is ESP-NOW?
ESP-NOW is a wireless communication protocoldeveloped by Espressif, allowing ESP32 boards to send and receive data directly without Wi-Fi or internet.
ð§ Key Features
- ðĄ Peer-to-peer communication (up to 20 devices)
- ⥠Low power and fast (few milliseconds delay)
- ð Encrypted data transmission
- ðŦ No Wi-Fi router or internet needed
- ð Bi-directional communication supported
ð Where to Use (Use Cases)
- ðŪ Wireless joystick controller
- ð Smart home automation
- ðĻ Personal safety devices (like Safeguard+)
- ðą Remote environment sensors
- ð Vehicle-to-vehicle communication
- ð College projects requiring mesh or local network
ð ïļ Components Needed
- â 2x ESP32 Boards
- â Micro USB cables
- â Arduino IDE installed
- â Sensor/input (e.g., joystick/keypad)
- â Output (e.g., LED, buzzer, OLED)
ð 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
âïļ Pinout (Example for Sender â 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 |
âïļ Pinout (Example RECEIVER)
| Neopixel Pin | ESP32 Pin |
|---|---|
| VCC | VCC |
| GNG | GND |
| DOUT | GPIO15 |
𧊠Applications
- ð Wireless button panel
- ðĶ Inventory scan/tag systems
- ð Battery-operated remote devices
- ð Secure, private IoT devices (no cloud dependency)
- ð Ideal for IEEE & hackathon projects
ðĄ 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)
ð Notes
- ðķ Keep both ESP32 on the same WiFi channel
- ð Use only MAC Address of peer (receiver)
- ðŽ Packet size should be under 250 bytes
- ð Both must be in WiFi STA mode
- ð ESP-NOW doesnât 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 = ""; Â // 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/ Â
 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 Â Â // Pin connected to the NeoPixel
#define NUM_PIXELS 4Â Â Â Â // 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() {
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