ThingSpeak Data Logging with ESP32: Channels, Fields and Live Charts

#include <WiFi.h>
#include <WiFiClientSecure.h>
#include <HTTPClient.h>
#include <DHT.h>

const char* WIFI_SSID = "YourWiFi";
const char* WIFI_PASS = "YourWiFiPassword";
const char* WRITE_KEY = "YOUR_WRITE_KEY";
const uint32_t PERIOD_MS = 20000;   // stay above the 15 s free-account limit

DHT dht(4, DHT22);
uint32_t lastUpdate = 0;

long sendToThingSpeak(float t, float h, int rssi) {
  WiFiClientSecure client;
  client.setInsecure();              // encrypts, but no certificate check
  HTTPClient http;
  if (!http.begin(client, "https://api.thingspeak.com/update")) return -1;
  http.addHeader("Content-Type", "application/x-www-form-urlencoded");

  String body = "api_key=" + String(WRITE_KEY) +
                "&field1=" + String(t, 1) +
                "&field2=" + String(h, 1) +
                "&field3=" + String(rssi);

  int code = http.POST(body);
  long entryId = -1;
  if (code == 200) {
    entryId = http.getString().toInt();   // 0 means rejected
  } else {
    Serial.printf("HTTP error %d", code);
    Serial.println();
  }
  http.end();
  return entryId;
}

void setup() {
  Serial.begin(115200);
  dht.begin();
  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASS);
  while (WiFi.status() != WL_CONNECTED) delay(500);
  Serial.println("WiFi connected");
}

void loop() {
  if (millis() - lastUpdate < PERIOD_MS) return;
  lastUpdate = millis();

  float t = dht.readTemperature();
  float h = dht.readHumidity();
  if (isnan(t) || isnan(h)) { Serial.println("DHT error, skipped"); return; }

  long id = sendToThingSpeak(t, h, WiFi.RSSI());
  if (id > 0)       Serial.printf("Entry %ld stored", id);
  else if (id == 0) Serial.print("Rejected: too fast or bad key");
  else              Serial.print("Request failed");
  Serial.println();
}