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By dilaritokitto
Dragomir Alin wrote:How can I solve this problem?


Code: Select all/*********
  Rui Santos
  Complete project details at

// Import required libraries
#include <Arduino.h>
#include <ESP8266WiFi.h>
#include <Hash.h>
#include <ESPAsyncTCP.h>
#include <ESPAsyncWebServer.h>
#include <Adafruit_Sensor.h>
#include <DHT.h>

// Replace with your network credentials
const char* ssid = "Selby";
const char* password = "66294894";

#define DHTPIN 2     // Digital pin connected to the DHT sensor

// Uncomment the type of sensor in use:
//#define DHTTYPE    DHT11     // DHT 11
#define DHTTYPE    DHT22     // DHT 22 (AM2302)
//#define DHTTYPE    DHT21     // DHT 21 (AM2301)


// current temperature & humidity, updated in loop()
float t = 0.0;
float h = 0.0;

// Create AsyncWebServer object on port 80
AsyncWebServer server(80);

// Generally, you should use "unsigned long" for variables that hold time
// The value will quickly become too large for an int to store
unsigned long previousMillis = 0;    // will store last time DHT was updated

// Updates DHT readings every 10 seconds
const long interval = 10000; 

const char index_html[] PROGMEM = R"rawliteral(
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="" integrity="sha384-fnmOCqbTlWIlj8LyTjo7mOUStjsKC4pOpQbqyi7RrhN7udi9RwhKkMHpvLbHG9Sr" crossorigin="anonymous">
    html {
     font-family: Arial;
     display: inline-block;
     margin: 0px auto;
     text-align: center;
    h2 { font-size: 3.0rem; }
    p { font-size: 3.0rem; }
    .units { font-size: 1.2rem; }
      font-size: 1.5rem;
      padding-bottom: 15px;
  <h2>ESP8266 DHT Server</h2>
    <i class="fas fa-thermometer-half" style="color:#059e8a;"></i>
    <span class="dht-labels">Temperature</span>
    <span id="temperature">%TEMPERATURE%</span>
    <sup class="units">&deg;C</sup>
    <i class="fas fa-tint" style="color:#00add6;"></i>
    <span class="dht-labels">Humidity</span>
    <span id="humidity">%HUMIDITY%</span>
    <sup class="units">%</sup>
setInterval(function ( ) {
  var xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
      document.getElementById("temperature").innerHTML = this.responseText;
  };"GET", "/temperature", true);
}, 10000 ) ;

setInterval(function ( ) {
  var xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
      document.getElementById("humidity").innerHTML = this.responseText;
  };"GET", "/humidity", true);
}, 10000 ) ;

// Replaces placeholder with DHT values
String processor(const String& var){
  if(var == "TEMPERATURE"){
    return String(t);
  else if(var == "HUMIDITY"){
    return String(h);
  return String();

void setup(){
  // Serial port for debugging purposes
  // Connect to Wi-Fi
  WiFi.begin(ssid, password);
  Serial.println("Connecting to WiFi");
  while (WiFi.status() != WL_CONNECTED) {

  // Print ESP8266 Local IP Address

  // Route for root / web page
  server.on("/", HTTP_GET, [](AsyncWebServerRequest *request){
    request->send_P(200, "text/html", index_html, processor);
  server.on("/temperature", HTTP_GET, [](AsyncWebServerRequest *request){
    request->send_P(200, "text/plain", String(t).c_str());
  server.on("/humidity", HTTP_GET, [](AsyncWebServerRequest *request){
    request->send_P(200, "text/plain", String(h).c_str());

  // Start server
void loop(){ 
  unsigned long currentMillis = millis();
  if (currentMillis - previousMillis >= interval) {
    // save the last time you updated the DHT values
    previousMillis = currentMillis;
    // Read temperature as Celsius (the default)
    float newT = dht.readTemperature();
    // Read temperature as Fahrenheit (isFahrenheit = true)
    //float newT = dht.readTemperature(true);
    // if temperature read failed, don't change t value
    if (isnan(newT)) {
      Serial.println("Failed to read from DHT sensor!");
    else {
      t = newT;
    // Read Humidity
    float newH = dht.readHumidity();
    // if humidity read failed, don't change h value
    if (isnan(newH)) {
      Serial.println("Failed to read from DHT sensor!");
    else {
      h = newH;

If you are using a devellopment module try pushing the boot button while uploading.
User avatar
By Anttiduino
#84636 Your ESP8266 is not in programming mode. When you program ESP8266 you must:

1) Connect GPIO0 to ground
2) Reset the circuit

After programming you must:

1) Open GPIO0 connection
2) Reset the circuit

How to do this depends on the development board you are using.
User avatar
By schufti
#84639 you are on a "newer" core (2.5.2) where the devs started to break most of the working stuff instead of fixing problems. Downgrade to 2.4.2 and it will work OOTB.
User avatar
By btidey
#84640 I used 2.5.2 for quite a while and had no problems downloading.

Currently I am on 2.6.0 and again have experienced no download problems.

The message being printed is typical of esptool trying to connect to a board that is not in serial download flash mode so I would tend to agree with the diagnosis of the GPIO0 / reset issues.