🛠 Communication inter-cartes avec ESP-NOW

Objectives

Make two Nano ESP32 boards communicate via ESP-NOW: peer-to-peer radio without a router or pairing, with frames up to 250 bytes. One transmitter broadcasts a counter, and a receiver displays it — the foundation of an autonomous sensor network.

Hardware

• 2 × Arduino Nano ESP32 + 2 USB-C cables
• Both boards on the same Wi-Fi channel (channel 0 = current channel)

Complete Code

// Émetteur (diffusion). Côté récepteur, décommenter la callback et son
// enregistrement dans setup.
#include <WiFi.h>
#include <esp_now.h>

uint8_t broadcast[] = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
uint32_t n = 0;

// void onRecu(const uint8_t* src, esp_now_recv_info_t* info,
//             const uint8_t* data, int8_t len) {
//   Serial.printf("reçu %.*s\n", len, data);
// }

void setup {
  Serial.begin(115200);
  WiFi.mode(WIFI_STA);            // ESP-NOW exige STA, sans connexion AP
  if (esp_now_init != ESP_OK) { Serial.println("ESP-NOW KO"); while (1); }
  // Récepteur : esp_now_register_recv_cb(onRecu);
  esp_now_peer_info_t peer = {};
  memcpy(peer.peer_addr, broadcast, 6);
  peer.channel = 0;               // 0 = canal courant
  peer.encrypt = false;
  esp_now_add_peer(&peer);
}

void loop {
  char msg[32];
  int len = snprintf(msg, sizeof msg, "hello #%lu", (unsigned long)n++);
  esp_now_send(broadcast, (uint8_t*)msg, len);
  Serial.println(msg);
  delay(1000);
}

Expected Verification

The receiver's serial monitor displays "hello #0", "hello #1"… every second, without any router. The exchange is direct between the two boards, with a range significantly greater than that of a distant access point.

Common Errors

• Missing WiFi.mode(WIFI_STA), or connecting to an AP on a different channel: frames are not sent.
• Payload larger than 250 bytes: esp_now_send fails silently.
• Receive callback not registered: the transmitter sends, but the receiver displays nothing.
• Mixing cores: the "Arduino ESP32 Boards" package documents ESP-NOW; with the Espressif core, callback signatures differ.