Getting NAN-Readings from DHT-11 Sensor

Question

I am trying to read temperature and humidity from a DHT-11 sensor with a arduino uno R3

#include <DHT.h>
#include <LiquidCrystal.h>

#define DHTPIN A3
#define DHTTYPE DHT11

DHT dht(DHTPIN,DHTTYPE);
LiquidCrystal lcd(5,8,9,10,11,12);

String hum="Humidity:";
String temptext="Temp:";

void setup() {

    Serial.begin(9600);
    lcd.clear();
    lcd.begin(16,2);
    dht.begin();
}

void loop() {

    float humidity = dht.readHumidity();
    delay(500);
    float temp = dht.readTemperature();
    delay(500);
      Serial.println(hum+humidity);
      Serial.println(temptext+temp);
      lcd.clear();
      lcd.print(hum + humidity);
      lcd.setCursor(0,2);
      lcd.print(temptext+temp);
      delay (5000);


}

I am sure that my wiring is correct. What would be possible reasons for the DHT-11 reporting nothing but NAN? Might it be broken (I just unpacked it)?

Answer 1

Reverse order:

Q: Might it be broken?

A: Unlikely. The only time I have had one go bad was when I connected the voltage backwards for too long. If it is just a short while it can survive that OK. But when it was too long it melted the thing.

Q: What are the possible reasons to see NaN?

A: Possible reasons:

1) You are using an Analog pin to receive a Digital signal.

2) A wire is loose

I regularly run several sensing stations that have 2 or 3 DHT-22s on them, and I use digital pins. Some of them are 20 feet away from the Arduino.

But if a wire comes loose I can see 0.00 for sure.

Here is a Q&A where I ask how to deal with those: gnuplot: Faulty sensor sometimes reading 0.00 - how to convert them to missing?

Of course the sensor isn't really faulty. It is always that I have pulled on a wire and it comes loose. Losing contact with any of the pins always gives the 0.00 readings.

So switch it over to a digital pin and see how it acts.

Here is my code:

Before setup(), do this:

//     2 devices:  Input pins D2 and D5
#include <Adafruit_Sensor.h>
#include "DHT.h"
#define DHTPIN 2    
#define DHTTYPE DHT22
DHT dht(DHTPIN, DHTTYPE);
#define DHT2PIN 5 
#define DHT2TYPE DHT22
DHT dht2(DHT2PIN, DHT2TYPE);

Then

void loop() {
  float h = dht.readHumidity();
  float t = dht.readTemperature();
  float df = t*(9.0/5.0)+32;
  if (isnan(h) || isnan(t)) { h=0; df=0; }
  float h2 = dht2.readHumidity();
  float t2 = dht2.readTemperature();
  float df2 = t2*(9.0/5.0)+32;
  if (isnan(h2) || isnan(t2)) { h2=0; df2=0; }
  Serial.print(h);  Serial.print("\t");
  Serial.print(df);  Serial.print("\t");
  Serial.print(h2);  Serial.print("\t");
  Serial.println(df2);
  delay(30000);
  }