Send sensor readings between two ESP32 boards—without a router

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/* Kadosh Build: receiver. Classic ESP32 DevKit; Arduino-ESP32 3.x.
   This learning link is unencrypted. Do not transmit secrets.
   Original example code, MIT license. */
#include <Arduino.h>
#include <WiFi.h>
#include <esp_now.h>
#include <esp_wifi.h>
#include <freertos/FreeRTOS.h>
#include <freertos/queue.h>
#include <math.h>
constexpr uint8_t CHANNEL = 1;
constexpr uint32_t MAGIC = 0x4B424C31;
struct Packet { uint32_t magic; uint32_t sequence; float temperatureC; float humidityPct; };
static_assert(sizeof(Packet) == 16, "Packet layout differs");
QueueHandle_t packets;
uint32_t lastPacketAt = 0, lastSequence = 0;
bool received = false, warned = false;
void onReceive(const esp_now_recv_info_t* info, const uint8_t* bytes, int len) {
  if (!info || len != sizeof(Packet)) return;
  Packet packet;
  memcpy(&packet, bytes, sizeof(packet));
  if (packet.magic != MAGIC || !isfinite(packet.temperatureC) || !isfinite(packet.humidityPct)) return;
  // Wi-Fi task callback: queue the reading and return promptly.
  xQueueSend(packets, &packet, 0);
}
void setup() {
  Serial.begin(115200);
  WiFi.mode(WIFI_STA); WiFi.setSleep(false);
  if (esp_wifi_set_channel(CHANNEL, WIFI_SECOND_CHAN_NONE) != ESP_OK) {
    Serial.println("Channel setup failed"); while (true) delay(1000);
  }
  Serial.print("Receiver STA MAC: "); Serial.println(WiFi.macAddress());
  packets = xQueueCreate(4, sizeof(Packet));
  if (!packets || esp_now_init() != ESP_OK || esp_now_register_recv_cb(onReceive) != ESP_OK) {
    Serial.println("ESP-NOW setup failed"); while (true) delay(1000);
  }
  lastPacketAt = millis();
  Serial.println("Ready on channel 1. Copy the MAC into the sender sketch.");
}
void loop() {
  Packet packet;
  if (xQueueReceive(packets, &packet, 0) == pdTRUE) {
    const uint32_t gap = received && packet.sequence > lastSequence ? packet.sequence - lastSequence - 1 : 0;
    // A lower sequence can be a sender reboot: establish a fresh baseline.
    lastSequence = packet.sequence; received = true; warned = false; lastPacketAt = millis();
    Serial.printf("seq=%lu temp=%.1fC humidity=%.1f%% gap=%lu\n", (unsigned long)packet.sequence, packet.temperatureC, packet.humidityPct, (unsigned long)gap);
  }
  if (!warned && millis() - lastPacketAt > 10000UL) {
    Serial.println(received ? "STALE: no new packet for 10 seconds" : "WAITING: no packet received yet");
    warned = true;
  }
  delay(5);
}

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/* Kadosh Build: DHT22 sender. Classic ESP32 DevKit; Arduino-ESP32 3.x.
   Install Adafruit DHT sensor library and Adafruit Unified Sensor.
   DHT22 DATA -> GPIO4; 10k pull-up from DATA to 3V3 for a bare sensor.
   Original example code, MIT license. */
#include <Arduino.h>
#include <WiFi.h>
#include <esp_now.h>
#include <esp_wifi.h>
#include <DHT.h>
#include <math.h>
constexpr uint8_t CHANNEL = 1, DHT_PIN = 4;
constexpr uint32_t MAGIC = 0x4B424C31;
// Replace all six bytes with the receiver's printed STA MAC. This is a placeholder.
uint8_t receiverMac[] = {0x24, 0x6F, 0x28, 0x00, 0x00, 0x01};
struct Packet { uint32_t magic; uint32_t sequence; float temperatureC; float humidityPct; };
static_assert(sizeof(Packet) == 16, "Packet layout differs");
DHT sensor(DHT_PIN, DHT22);
uint32_t sequence = 0, previous = 0;
void setup() {
  Serial.begin(115200); sensor.begin();
  WiFi.mode(WIFI_STA); WiFi.setSleep(false);
  if (esp_wifi_set_channel(CHANNEL, WIFI_SECOND_CHAN_NONE) != ESP_OK || esp_now_init() != ESP_OK) {
    Serial.println("ESP-NOW setup failed"); while (true) delay(1000);
  }
  esp_now_peer_info_t peer = {};
  memcpy(peer.peer_addr, receiverMac, 6);
  peer.channel = CHANNEL; peer.ifidx = WIFI_IF_STA; peer.encrypt = false;
  if (esp_now_add_peer(&peer) != ESP_OK) {
    Serial.println("Peer setup failed"); while (true) delay(1000);
  }
  Serial.println("Sender ready. Receiver must use the same channel.");
}
void loop() {
  if (millis() - previous < 2500UL) return;
  previous = millis();
  const float t = sensor.readTemperature(), h = sensor.readHumidity();
  if (isnan(t) || isnan(h)) { Serial.println("DHT read failed: check wiring and pull-up"); return; }
  Packet packet = {MAGIC, ++sequence, t, h};
  const esp_err_t result = esp_now_send(receiverMac, reinterpret_cast<const uint8_t*>(&packet), sizeof(packet));
  Serial.printf("seq=%lu temp=%.1fC humidity=%.1f%% %s\n", (unsigned long)sequence, t, h, result == ESP_OK ? "queued (check receiver log)" : "queue failed");
}