已从DHT22获得NaN应答

Question

我正在尝试从DHT22读取温度和湿度，代码如下：

#include "fsm_config.h"
#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <DHT.h>

#define DHTPIN D4          // what pin we're connected to
#define DHTTYPE DHT22     // DHT 22  (AM2302)
DHT dht(DHTPIN, DHTTYPE); //// Initialize DHT sensor for normal 16mhz Arduino
const int buttonPin = D5;    // definicao do pino utilizado pelo botao
const int ledPin = D7;       // definicao do pino utilizado pelo led
const char* ssid = "augusto-Aspire-E5-571"; // id da rede
const char* password = "sLPCwZqX"; // senha da rede
const char* mqtt_server = "things.ubidots.com"; // server    

int buttonState = LOW;             // armazena a leitura atual do botao
int lastButtonState = LOW;         // armazena a leitura anterior do botao
unsigned long lastDebounceTime = 0;  // armazena a ultima vez que a leitura da entrada variou
unsigned long debounceDelay = 50;    // tempo utilizado para implementar o debounce
float umidade;  //Stores humidity value
float temperatura; //Stores temperature value
String hum = "{\"value\":";
String temp = "{\"value\":";
char humChar[50];
char tempChar[50];

WiFiClient espClient;
PubSubClient client(espClient);
int lastMsg = 1000;
int now;
char msg[60];
char msg1[60];

int send_data() {
  dht.begin();
  umidade = dht.readHumidity();
  temperatura = dht.readTemperature();
  //Print temp and humidity values to serial monitor
  Serial.print("Humidity: ");
  Serial.print(umidade);
  Serial.print(" %, Temp: ");
  Serial.print(temperatura);
  Serial.println(" Celsius");
  temp.concat(temperatura);
  temp.concat("}");
  hum.concat(umidade);
  hum.concat("}");
  temp.toCharArray(tempChar, 50);
  hum.toCharArray(humChar, 50);
  String hum = "{\"value\":";
  String temp = "{\"value\":";
  client.publish("/v1.6/devices/wemos/umidade", humChar);
  client.publish("/v1.6/devices/wemos/temp", humChar);

  delay(10000); //Delay 2 sec.
  return true;
}

但是我只得到了"NaN“作为答案，应该发生什么？我在这里寻找了一些其他问题，但没有一个对我有用。

这里是连接图像的链接：

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Answer 1

NaN代表“不是一个数字”。有时传感器无法读取，并会给出一个NaN值。您无法对其执行任何操作，但是在DHT.h库中有一个名为isnan()的函数。所以你可以在存储最后一个正确的值时创建一个备份变量。然后，您可以检查您的传感器是否显示为nan，如果他显示，您可以打印出备份变量：

float temperature;
float bTemperature;

temperature = dht.readTemperature();

if(!isnan(temperature)){
  bTemperature = temperature;
  Serial.println(temperature);

}
else{
  Serial.println(bTemperature);
}