Failed to read from DHT11 sensor NodeMCU

[UsamaAmjad]

I am trying to use DHT11 with Blynk App. It was working perfectly fine 2 months ago. Today I am trying to use it again but no matter what I try, it just doesn’t work.

What I have already tried:

1. Changing my sensor with a new one
2. Updated Blynk libraries
3. Trying different pins

Can anyone please help me to identify the problem?

[This is my exact circuit diagram](https://diygeeks.org/wp-content/uploads/2018/03/dht-iot.jpg)

Error Log:

[20718] Connecting to AndroidAP
[21221] Connected to WiFi
[21221] IP: 192.168.43.114
[21221] 
    ___  __          __
   / _ )/ /_ _____  / /__
  / _  / / // / _ \/  '_/
 /____/_/\_, /_//_/_/\_\
        /___/ v0.5.4 on NodeMCU

[21302] Connecting to blynk-cloud.com:80
[31303] Connecting to blynk-cloud.com:80
[32040] Ready (ping: 180ms).
Failed to read from DHT sensor!
Failed to read from DHT sensor!
Failed to read from DHT sensor!

Code:

#define BLYNK_PRINT Serial    // Comment this out to disable prints and save space
#include <SPI.h>
#include <ESP8266WiFi.h>
#include <BlynkSimpleEsp8266.h>
#include <SimpleTimer.h>
#include <DHT.h>

// You should get Auth Token in the Blynk App.
// Go to the Project Settings (nut icon).
char auth[] = "my_token"; //Enter the Auth code which was send by Blink

// Your WiFi credentials.
// Set password to "" for open networks.
char ssid[] = "AndroidAP";  //Enter your WIFI Name
char pass[] = "my_pass";  //Enter your WIFI Password

#define DHTPIN 0          // Digital pin D3

// Uncomment whatever type you're using!
#define DHTTYPE DHT11     // DHT 11

DHT dht(DHTPIN, DHTTYPE);
SimpleTimer timer;


void sendSensor()
{
  float h = dht.readHumidity();
  float t = dht.readTemperature(); // or dht.readTemperature(true) for Fahrenheit

  if (isnan(h) || isnan(t)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }
  // You can send any value at any time.
  // Please don't send more that 10 values per second.
  Blynk.virtualWrite(V5, h);  //V5 is for Humidity
  Blynk.virtualWrite(V6, t);  //V6 is for Temperature
  Blynk.virtualWrite(V7, h); // Humidity for graph
  Blynk.virtualWrite(V8, t); // Temperature for 
}

void setup()
{
  Serial.begin(9600); // See the connection status in Serial Monitor
  Blynk.begin(auth, ssid, pass);

  dht.begin();

  // Setup a function to be called every 5 second
  timer.setInterval(5000L, sendSensor);
}

void loop()
{
  Blynk.run(); // Initiates Blynk
  timer.run(); // Initiates SimpleTimer
}

This is my settings and it was working previously. I also tried to change it to NodeMCU 1.0 (ESP 12E Module) but still not working.

[PeteKnight]

There have been a few posts recently about some DHT libraries not working well with Blynk, like this one:

DHT11 Works, unless I use Blynk.begin()

I’m using a nodemcu es8266 to read the temperature from the DHT11. I’ve posted my code below, and it works until I uncomment the line where I have my Blink.begin() statement. This seems to be the only thing that causes my DHT11 to go from working to returning NaN values. I’m not sure how to get this to work, but I’ve isolated the cause to the parts of the code that connect to Blynk. #include <DHT.h> #include <DHT_U.h> #include <ESP8266WiFi.h> #include <BlynkSimpleEsp8266.h> #define DHTTYPE DHT…

Personally, I don’t use DHT sensors because they are so inaccurate, so have no first-hand knowledge of using these with Blynk.

Maybe switching to something like the BME280 is a better long term solution anyway.

Pete.

[ericssson]

If you have an Arduino Uno or something try with that, because it may be a DHT11 problem… I do use “lits” of DHT22 and they work OK. Which dht library do you use? I use the one from Adafruit (you need to install 2 libs described HERE ). I would also switch to a different GPIO, say GPIO5 or GPIO4 (D1, D2 on NodeMCU)…

[UsamaAmjad]

Thanks everyone, the connectors were faulty I changed the connected wires and it starts working again. Wasted my 4 5 hours

[UsamaAmjad]

DHT sensors are indeed inaccurate. BME280 and BME680 seem good I will try it. Actually I am building it for my hydroponic greenhouse.
Can you also suggest good sensors for water pH and TDS check?

I found this one for pH but not sure if they are reliable or not.

[PeteKnight]

No experience of Ph or TDS I’m afraid, but I would imagine that any sensor that’s permanently immersed in water or soil, and has a current applied across it either permanently or frequently will have a limited life due to the electrolysis effect on the sensor elements.

Might be worth going for the cheapest you can find and replacing frequently.

Pete.