Coding Grouping Light

ESP-NOW

ESP-NOW is a connectionless communication protocol developed by Espressif. It functions similarly to Wi-Fi (802.11) but offers lower power consumption and minimal latency, making it ideal for point-to-point communication in IoT applications.

Key Features:

No Wi-Fi configuration required.
Low power consumption and low latency.
Supports both one-to-one and one-to-many communication.

1. Unicast Communication (One-to-One)

Receiver Sketch Example

#include <esp_now.h>   // ESP-NOW library
#include <WiFi.h>      // Wi-Fi functions

// Structure to hold an incoming text message
struct MessagePacket {
  char text[32];
};

// Callback when data arrives
void onMessageReceived(const esp_now_recv_info_t *info, const uint8_t *data, int len) {
  MessagePacket receivedPacket;
  memcpy(&receivedPacket, data, sizeof(receivedPacket));  // Copy payload

  // Print sender's MAC address
  char senderMac[18];
  snprintf(senderMac, sizeof(senderMac), "%02X:%02X:%02X:%02X:%02X:%02X",
           info->src_addr[0], info->src_addr[1], info->src_addr[2],
           info->src_addr[3], info->src_addr[4], info->src_addr[5]);
  Serial.print("Received from MAC: "); Serial.println(senderMac);

  // Print message text
  Serial.print("Received message: "); Serial.println(receivedPacket.text);
}

void setup() {
  Serial.begin(115200);              // Start serial logging
  WiFi.mode(WIFI_STA);               // Set to station mode
  delay(100);                        // Short delay to ensure MAC address is ready

  // Show this board's MAC for peer registration
  Serial.print("This Receiver's MAC: ");
  Serial.println(WiFi.macAddress());

  esp_now_init();                    // Initialize ESP-NOW
  esp_now_register_recv_cb(onMessageReceived);  // Register receive callback
}

void loop() {
  // Nothing needed here; callback handles incoming messages
}

Receiver Sketch Explanation

</aside>

Upload Receiver sketch first, and note down the MAC address from serial monitor:

This Receiver's MAC: AA:BB:CC:DD:EE:FF

Sender Sketch Example

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

// Structure for the outgoing text message
struct MessagePacket {
  char text[32];
};

MessagePacket sendPacket;             // Buffer for outgoing message
int sendMessageCount = 0;             // Counter for sent messages

// Replace with the Receiver's MAC address shown in its Serial Monitor
uint8_t receiverAddress[6] = {0x24,0x6F,0x28,0xAB,0xCD,0xEF};

void setup() {
  Serial.begin(115200);                // Start serial logging
  WiFi.mode(WIFI_STA);                 // Station mode
  delay(100);                          // Ensure MAC ready

  esp_now_init();                      // Initialize ESP-NOW

  esp_now_peer_info_t peerInfo = {};
  memcpy(peerInfo.peer_addr, receiverAddress, 6);
  peerInfo.channel = 0;
  peerInfo.encrypt = false;
  esp_now_add_peer(&peerInfo);         // Register the Receiver as a peer
}

void loop() {
  sendMessageCount++;                  // Increment send counter
  // Prepare message with embedded counter
  snprintf(sendPacket.text, sizeof(sendPacket.text), "Msg #%d from ESP32", sendMessageCount);

  // Send the packet
  bool ok = (esp_now_send(receiverAddress, (uint8_t *)&sendPacket, sizeof(sendPacket)) == ESP_OK);
  Serial.print(ok ? "Sent: " : "Failed: ");
  Serial.println(sendPacket.text);

  delay(2000);  // Send every 2 seconds
}

Sender Sketch Explanation: