A Telegram bot on the ESP32: your home from your phone

Send /status to your bot on Telegram and it replies with the temperature at home; send /led_on and a light turns on. It works from anywhere, even away from home, without opening ports on the router: it is the board that goes and asks Telegram for messages.

// Telegram bot: turn the LED on and off and ask for the temperature from your phone. It only answers your chat.
#include <WiFi.h>
#include <WiFiClientSecure.h>
#include <UniversalTelegramBot.h>
#include <Adafruit_BME280.h>

const char* NETWORK = "your-network-name";
const char* PASSWORD = "your-network-password";
#define TOKEN "123456789:the-token-BotFather-gave-you"   // secret: never publish it
const String MY_CHAT = "123456789";                      // your chat number (step 3)

const int LED = 2;
WiFiClientSecure client;
UniversalTelegramBot bot(TOKEN, client);
Adafruit_BME280 bme;
unsigned long lastCheck = 0;

void reply(int count) {
  for (int i = 0; i < count; i++) {
    String chat = bot.messages[i].chat_id;
    String text = bot.messages[i].text;
    if (chat != MY_CHAT) {                       // a stranger: do not obey
      bot.sendMessage(chat, "You are not authorized.", "");
      continue;
    }
    if (text == "/led_on") {
      digitalWrite(LED, HIGH);
      bot.sendMessage(chat, "LED on", "");
    } else if (text == "/led_off") {
      digitalWrite(LED, LOW);
      bot.sendMessage(chat, "LED off", "");
    } else if (text == "/status") {
      String r = "Temperature: " + String(bme.readTemperature(), 1) + " °C\n";
      r += "Humidity: " + String(bme.readHumidity(), 0) + " %\n";
      r += "LED: " + String(digitalRead(LED) ? "on" : "off");
      bot.sendMessage(chat, r, "");
    } else {
      bot.sendMessage(chat, "Commands: /led_on, /led_off, /status", "");
    }
  }
}

void setup() {
  Serial.begin(115200);
  pinMode(LED, OUTPUT);
  if (!bme.begin(0x77)) Serial.println("BME280 not found: check the wires");
  WiFi.mode(WIFI_STA);
  WiFi.begin(NETWORK, PASSWORD);
  client.setCACert(TELEGRAM_CERTIFICATE_ROOT);   // the certificate to talk to Telegram securely
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  configTime(0, 0, "pool.ntp.org");              // the exact time, as in the library example
  Serial.println("\nConnected. Write to your bot.");
}

void loop() {
  if (millis() - lastCheck > 1000) {             // one check per second, as in the library example
    int newCount = bot.getUpdates(bot.last_message_received + 1);
    while (newCount) {
      reply(newCount);
      newCount = bot.getUpdates(bot.last_message_received + 1);
    }
    lastCheck = millis();
  }
}