Unable to use DHT22 with TTGO T-Call ESP32

Hi, I'm trying to use DHT22 with TTGO T-Call ESP32. But, its not working. It is continuously failing to receive data from the sensor. I have tried connecting the vcc of the sensor to the 3.3V, 5V and Vin pin of TTGO T-Call ESP32, but nothing works. On the other hand, it works fine with ESP32 Dev module. I'm unable to find out whats wrong here. While uploading code at TTGO T-Call ESP32, I choose the ESP32 Wrover module. There is no problem with uploading the data. I found this code on the internet. Please help me.

#include "WiFi.h"
#include "ESPAsyncWebServer.h"
#include <Adafruit_Sensor.h>
#include <DHT.h>


// Replace with your network credentials
const char* ssid = "Tesla";
const char* password = "isc20177";

#define DHTPIN 27     // 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)

DHT dht(DHTPIN, DHTTYPE);

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

String readDHTTemperature() { 
  // Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
  // Read temperature as Celsius (the default)
  float t = dht.readTemperature();
  // Read temperature as Fahrenheit (isFahrenheit = true)
  //float t = dht.readTemperature(true);
  // Check if any reads failed and exit early (to try again).
  if (isnan(t)) {    
    Serial.println("Failed to read from DHT sensor!");
    return "--";
  }
  else {
    Serial.println(t);
    return String(t);
  }
}

String readDHTHumidity() {
  // Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
  float h = dht.readHumidity();
  if (isnan(h)) {
    Serial.println("Failed to read from DHT sensor!");
    return "--";
  }
  else {
    Serial.println(h);
    return String(h);
  }
}

const char index_html[] PROGMEM = R"rawliteral(
<!DOCTYPE HTML><html>
<head>
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.7.2/css/all.css" integrity="sha384-fnmOCqbTlWIlj8LyTjo7mOUStjsKC4pOpQbqyi7RrhN7udi9RwhKkMHpvLbHG9Sr" crossorigin="anonymous">
  <style>
    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; }
    .dht-labels{
      font-size: 1.5rem;
      vertical-align:middle;
      padding-bottom: 15px;
    }
  </style>
</head>
<body>
  <h2>ESP32 DHT Server</h2>
  <p>
    <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>
  </p>
  <p>
    <i class="fas fa-tint" style="color:#00add6;"></i> 
    <span class="dht-labels">Humidity</span>
    <span id="humidity">%HUMIDITY%</span>
    <sup class="units">&percnt;</sup>
  </p>
</body>
<script>
setInterval(function ( ) {
  var xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
      document.getElementById("temperature").innerHTML = this.responseText;
    }
  };
  xhttp.open("GET", "/temperature", true);
  xhttp.send();
}, 10000 ) ;

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

// Replaces placeholder with DHT values
String processor(const String& var){
  //Serial.println(var);
  if(var == "TEMPERATURE"){
    return readDHTTemperature();
  }
  else if(var == "HUMIDITY"){
    return readDHTHumidity();
  }
  return String();
}

void setup(){
  // Serial port for debugging purposes
  Serial.begin(115200);

  dht.begin();
  
  // Connect to Wi-Fi
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.println("Connecting to WiFi..");
  }

  // Print ESP32 Local IP Address
  Serial.println(WiFi.localIP());

  // 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", readDHTTemperature().c_str());
  });
  server.on("/humidity", HTTP_GET, [](AsyncWebServerRequest *request){
    request->send_P(200, "text/plain", readDHTHumidity().c_str());
  });

  // Start server
  server.begin();
}
 
void loop(){
  
}

Hi,
Have you included the pull up resistor that is suggested with the DHT22?

Tom... :smiley: :+1: :coffee: :australia:

Unfortunately you failed to provide links to the used hardware. If your TTGO board is the one from Lilygo you simply used a pin to connect the DHT which is already used by the onboard SIM800 module.

Yes, my board is from lilygo. I tried with digital 2,4,27 on different occasions. But none of them produced any results.

Yes, I tried with a 4.7k ohm resistor, but still there was no value.

Hi,
Have you tried the execises at this tutorial site?

Tom... :smiley: :+1: :coffee: :australia:

4 is also used by the SIM module. Did you actually looked at the module documentation before wiring your setup?

While you used pin 2 did you adapt the code accordingly?

Post a complete wiring diagram and the changed code!

Yes I did

That probably means there's something wrong in the circuit or the code. Post a complete wiring diagram and the complete (adapted) code! Post links to all used hardware! Post links to the used libraries (there are at least 4 libraries out there called DHT.h)!


I have connected the Vcc of the DHT22 to the Vin of the TTgo board, Signal pin of the sensor board to the digital pin 27 of the ttgo board, also connected a 4.7k ohm resistor between the signal pin and the vcc line and connected the ground to the ground. And I'm using the DHT library which is available in the arduino IDE. Later, I tried connecting the signal pin to digital pin 26,15,2. But still there was no data. With the same code and same wiring(connecting signal pin of sensor to digital pin 2 of ttgo board) I was able to receive data from esp32 easily.

#include "WiFi.h"
#include "ESPAsyncWebServer.h"
#include <Adafruit_Sensor.h>
#include <DHT.h>


// Replace with your network credentials
const char* ssid = "Tesla";
const char* password = "isc20177";

#define DHTPIN 27     // 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)

DHT dht(DHTPIN, DHTTYPE);

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

String readDHTTemperature() { 
  // Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
  // Read temperature as Celsius (the default)
  float t = dht.readTemperature();
  // Read temperature as Fahrenheit (isFahrenheit = true)
  //float t = dht.readTemperature(true);
  // Check if any reads failed and exit early (to try again).
  if (isnan(t)) {    
    Serial.println("Failed to read from DHT sensor!");
    return "--";
  }
  else {
    Serial.println(t);
    return String(t);
  }
}

String readDHTHumidity() {
  // Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
  float h = dht.readHumidity();
  if (isnan(h)) {
    Serial.println("Failed to read from DHT sensor!");
    return "--";
  }
  else {
    Serial.println(h);
    return String(h);
  }
}

const char index_html[] PROGMEM = R"rawliteral(
<!DOCTYPE HTML><html>
<head>
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.7.2/css/all.css" integrity="sha384-fnmOCqbTlWIlj8LyTjo7mOUStjsKC4pOpQbqyi7RrhN7udi9RwhKkMHpvLbHG9Sr" crossorigin="anonymous">
  <style>
    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; }
    .dht-labels{
      font-size: 1.5rem;
      vertical-align:middle;
      padding-bottom: 15px;
    }
  </style>
</head>
<body>
  <h2>ESP32 DHT Server</h2>
  <p>
    <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>
  </p>
  <p>
    <i class="fas fa-tint" style="color:#00add6;"></i> 
    <span class="dht-labels">Humidity</span>
    <span id="humidity">%HUMIDITY%</span>
    <sup class="units">&percnt;</sup>
  </p>
</body>
<script>
setInterval(function ( ) {
  var xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
      document.getElementById("temperature").innerHTML = this.responseText;
    }
  };
  xhttp.open("GET", "/temperature", true);
  xhttp.send();
}, 10000 ) ;

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

// Replaces placeholder with DHT values
String processor(const String& var){
  //Serial.println(var);
  if(var == "TEMPERATURE"){
    return readDHTTemperature();
  }
  else if(var == "HUMIDITY"){
    return readDHTHumidity();
  }
  return String();
}

void setup(){
  // Serial port for debugging purposes
  Serial.begin(115200);

  dht.begin();
  
  // Connect to Wi-Fi
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.println("Connecting to WiFi..");
  }

  // Print ESP32 Local IP Address
  Serial.println(WiFi.localIP());

  // 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", readDHTTemperature().c_str());
  });
  server.on("/humidity", HTTP_GET, [](AsyncWebServerRequest *request){
    request->send_P(200, "text/plain", readDHTHumidity().c_str());
  });

  // Start server
  server.begin();
}
 
void loop(){
  
}`Preformatted text`

And, an imporatnt bit, how are you powering the board ?

Hi,
Random Nerd suggests for the TTGO T-Call ESP32;

To upload code to your board, go to Tools > Board and select ESP32 Dev module .

Tom.. :smiley: :+1: :coffee: :australia:

I power it using a usb cable from my desktop computer

I tried this too, but didn't find any luck. I also tried with DOIT dev module, TTGO v1 at the board manager

Any updates on this? I have the same problem.

I soldered the pins of the esp32 again. Now, it works. I guess due to improper soldering, the sensor was not getting enough power from 3.3V pin.

1 Like