I am writing a code to read DHT11 value and control 4 relay but temp. sensor is showing me "nan" everytime - mqtt

Question

I am making a project on home automation with temperature reading using NodeMCU (ESP8266-12E). I am using a DHT11 sensor with DHT11.h library, but my temperature sensor is showing me "nan" instead of any value. I don't know where I am lagging.
My code is given below:
#include "DHT.h" // including the library of DHT11 temperature and humidity sensor
#define DHTTYPE DHT11 // DHT 11
#include <ESP8266WiFi.h>
#include "Adafruit_MQTT.h"
#include "Adafruit_MQTT_Client.h"
#define Relay1 D1
#define Relay2 D2
#define Relay3 D3
#define Relay4 D4
#define DHTPIN D0
DHT dht(DHTPIN, DHTTYPE);
float temp_f;
String webString = "";
unsigned long previousMillis = 0;
const long interval = 2300;
#define WLAN_SSID "internet" // Your SSID
#define WLAN_PASS "*********" // Your password
/************************* Adafruit.io Setup *********************************/
#define AIO_SERVER "io.adafruit.com" //Adafruit Server
#define AIO_SERVERPORT 1883
#define AIO_USERNAME "foo" // Username
#define AIO_KEY "bar" // Auth Key
//WIFI CLIENT
WiFiClient client;
Adafruit_MQTT_Client mqtt(&client, AIO_SERVER, AIO_SERVERPORT, AIO_USERNAME, AIO_KEY);
// Setup a feed called 'photocell' for publishing.
// Notice MQTT paths for AIO follow the form: <username>/feeds/<feedname>
const char TEMP_FEED[] PROGMEM = AIO_USERNAME "/feeds/photocell";
Adafruit_MQTT_Publish photocell = Adafruit_MQTT_Publish(&mqtt, AIO_USERNAME"/feeds/photocell");
Adafruit_MQTT_Subscribe Light1 = Adafruit_MQTT_Subscribe(&mqtt, AIO_USERNAME"/feeds/Relay1"); // Feeds name should be same everywhere
Adafruit_MQTT_Subscribe Light2 = Adafruit_MQTT_Subscribe(&mqtt, AIO_USERNAME"/feeds/Relay2");
Adafruit_MQTT_Subscribe Light3 = Adafruit_MQTT_Subscribe(&mqtt, AIO_USERNAME"/feeds/Relay3");
Adafruit_MQTT_Subscribe Light4 = Adafruit_MQTT_Subscribe(&mqtt, AIO_USERNAME"/feeds/Relay4");
void MQTT_connect();
void setup()
{
Serial.begin(115200);
delay(10);
dht.begin();
// Print temperature sensor details.
pinMode(Relay1, OUTPUT);
pinMode(Relay2, OUTPUT);
pinMode(Relay3, OUTPUT);
pinMode(Relay4, OUTPUT);
// Connect to WiFi access point.
Serial.println();
Serial.println();
Serial.print("Connecting to ");
Serial.println(WLAN_SSID);
WiFi.begin(WLAN_SSID, WLAN_PASS);
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
Serial.println();
Serial.println("WiFi connected");
Serial.println("IP address: ");
Serial.println(WiFi.localIP());
temp_f = dht.readTemperature(true);
Serial.println();
Serial.print("Initial Temp: ");
Serial.println(temp_f);
Serial.println();
mqtt.subscribe(&Light1);
mqtt.subscribe(&Light3);
mqtt.subscribe(&Light2);
mqtt.subscribe(&Light4);
}
int delayTime = 300000; //Wait 5 minutes before sending data to web
int startDelay = 0;
void loop()
{
MQTT_connect();
if (millis() - startDelay < delayTime) {
Serial.println("waiting delaytime");
}
else {
temp_f = dht.readTemperature(true); //Get temp in Farenheit
startDelay = millis();
Serial.print(F("\nSending temp: "));
Serial.print(temp_f);
Serial.print("...");
if (!photocell.publish(temp_f)) { //Publish to Adafruit
Serial.println(F("Failed"));
}
else {
Serial.println(F("Sent!"));
}
}
/* //int t = dht.readTemperature(true);
// t = t/100000000;
Serial.print(F("\nSending photocell val "));
Serial.print(t);
Serial.print("...");
if (! photocell.publish(t)) {
Serial.println(F("Failed"));
} else {
Serial.println(F("OK!"));
}*/
Adafruit_MQTT_Subscribe* subscription;
while ((subscription = mqtt.readSubscription(2000))) {
if (subscription == &Light1) {
Serial.print(F("Got: "));
Serial.println((char*)Light1.lastread);
int Light1_State = atoi((char*)Light1.lastread);
digitalWrite(Relay1, Light1_State);
}
if (subscription == &Light2) {
Serial.print(F("Got: "));
Serial.println((char*)Light2.lastread);
int Light2_State = atoi((char*)Light2.lastread);
digitalWrite(Relay2, Light2_State);
}
if (subscription == &Light3) {
Serial.print(F("Got: "));
Serial.println((char*)Light3.lastread);
int Light3_State = atoi((char*)Light3.lastread);
digitalWrite(Relay3, Light3_State);
}
if (subscription == &Light4) {
Serial.print(F("Got: "));
Serial.println((char*)Light4.lastread);
int Light4_State = atoi((char*)Light4.lastread);
digitalWrite(Relay4, Light4_State);
}
}
// this is our 'wait for incoming subscription packets and callback em' busy subloop
// try to spend your time here:
mqtt.processPackets(500);
}
void MQTT_connect()
{
int8_t ret;
if (mqtt.connected()) {
return;
}
Serial.print("Connecting to MQTT... ");
uint8_t retries = 3;
while ((ret = mqtt.connect()) != 0) {
Serial.println(mqtt.connectErrorString(ret));
Serial.println("Retrying MQTT connection in 5 seconds...");
mqtt.disconnect();
delay(5000);
retries--;
if (retries == 0) {
while (1);
}
}
Serial.println("MQTT Connected!");
}

Answer 1

you try to read temperature and humidity in setup(). but you need to wait 2s at minima after the dht.begin and before reading, because Sensor readings may also be up to 2 seconds
so add delay(2000) before the first reading..