Nodemcu ESP8266搭配DHT22传感器出现nan值问题求助

问题描述 #

我用NodeMCU ESP8266搭配DHT22传感器搭建的系统，运行数天后串口监视器输出的温湿度值变成了nan，这个异常值还干扰了Adafruit Dashboard的数据读取。截至2023年2月6日发帖前两日，系统仍能正常输出正确数值。

使用的库 #

• Adafruit Unified Sensor
• ArduinoHttpclient
• Ethernet
• WiFi101
• Adafruit IO Arduino及依赖库

系统代码 #

// Adafruit IO Temp e Hum com Switch 
// Tutorial Link: https://learn.adafruit.com/adafruit-io-basics-temperature-and-humidity

/************************** Configuration ***********************************/

// edit the config.h tab and enter your Adafruit IO credentials
#define IO_USERNAME  "*****"
#define IO_KEY       "*****"
// and any additional configuration needed for WiFi, cellular,
#define WIFI_SSID "*****"
#define WIFI_PASS "*****"
// or ethernet clients.
#include <AdafruitIO.h>
#include <AdafruitIO_WiFi.h>
#include <AdafruitIO_MQTT.h>

#include "config.h"

/************************ Comeca Aqui! *******************************/
//Sensor DHT
#include <Adafruit_Sensor.h>
#include <DHT.h>
#include <DHT_U.h>

// pin connected to DH22 data line
#define DATA_PIN 2//D2


//Esp library
#include <ESP8266WiFi.h>

// create DHT22 instance
DHT_Unified dht(DATA_PIN, DHT22);

// set up the 'temperature' and 'humidity' feeds
AdafruitIO_Feed *temperature = io.feed("temperature");
AdafruitIO_Feed *humidity = io.feed("humidity");
AdafruitIO_Feed *light = io.feed("lightfeed");

// Define correct feeds relays
AdafruitIO_Feed *pumpfeed = io.feed("pumpfeed"); 
AdafruitIO_Feed *fanfeed = io.feed("fanfeed");
AdafruitIO_Feed *lightfeed = io.feed("lightfeed");

// Define pins relays
 int fanPin = 13; // Pin GPIO13 (D7) controll fanfeed relay
 int pumpPin = 5; // Pin GPIO5 (D1) controll pumpfeed relay
 int lightPin = 15; // Pin GPIO15 (D8) controll pumpfeed relay

void setup() {
  // start the serial connection
  Serial.begin(9600);

  // wait for serial monitor to open
  while(! Serial);

  // connect to WiFi 
  io.connect();
  // Initialize pins as output
  pinMode(pumpPin, OUTPUT);
  pinMode(fanPin, OUTPUT);
   pinMode(lightPin, OUTPUT);

  // initialize dht22
  dht.begin();

  // connect to io.adafruit.com
  Serial.print("Connectando ao Adafruit IO");
  io.connect();

  // wait for a connection
  while(io.status() < AIO_CONNECTED) {
    Serial.print(".");
    delay(500);
  }

  // we are connected
  Serial.println();
  Serial.println(io.statusText());

  //--

  // Define the callback functions for the feeds 
  pumpfeed->onMessage(pumpChange);
  fanfeed->onMessage(fanChange);
   lightfeed->onMessage(lightChange);

}

void loop() {

  // io.run(); is required for all sketches.
  // it should always be present at the top of your loop
  // function. it keeps the client connected to
  // io.adafruit.com, and processes any incoming data.
  io.run();

  Serial.println("Condições climáticas:"); //conditions
  sensors_event_t event;
  dht.temperature().getEvent(&event);

  float celsius = event.temperature;
  

  Serial.print("Celsius: ");
  Serial.print(celsius);
  Serial.println("°C");

  // save or celsius to Adafruit IO
  temperature->save(celsius);

  dht.humidity().getEvent(&event);

  Serial.print("Umidade: ");
  Serial.print(event.relative_humidity);
  Serial.println("%");

  // save humidity to Adafruit IO
  humidity->save(event.relative_humidity);

  // wait 5 seconds (5000 milliseconds == 5 seconds)
  delay(5000);

}

// Relays
void pumpChange(AdafruitIO_Data *data) {
  int value = data->toInt();
  //Serial.print("Valor recebido para pumpPin: "); //"value for pumpin"
  Serial.println(value);
  
  if (value == 1) {
    digitalWrite(pumpPin, HIGH);
    Serial.println("Bomba ligada!"); //ON
  } else {
    digitalWrite(pumpPin, LOW);
    Serial.println("Bomba desligada!"); //OFF
  }
}

void fanChange(AdafruitIO_Data *data) {
  int value = data->toInt();
  Serial.println(value);
  //Serial.print("Valor recebido para fanPin: ");
  if (value == 1) {
    digitalWrite(fanPin, HIGH);
    Serial.println("Ventilador ligado!"); //ON
  } else {
    digitalWrite(fanPin, LOW);
    Serial.println("Ventilador desligado!"); //OFF
  }
}

void lightChange(AdafruitIO_Data *data) {
  int value = data->toInt();
  Serial.println(value);
  //Serial.print("Valor recebido para lightPin: ");
  if (value == 1) {
    digitalWrite(lightPin, HIGH);
    Serial.println("Luz ligada!"); //ON
  } else {
    digitalWrite(lightPin, LOW);
    Serial.println("Luz desligada!"); //OFF
  }
}

已尝试的排查操作 #

• 将DHT22的数据引脚更换为其他无复位功能的可用引脚
• 更换库的旧版本进行测试
• 更换传感器的跳线

排查与解决建议 #

1. 传感器硬件稳定性优化 #

• 检查供电稳定性：给DHT22的供电回路添加100uF电解电容+100nF陶瓷电容滤波，避免电压波动影响传感器工作；同时确认ESP8266的电源适配器功率足够（至少5V/1A），防止继电器启动导致电压骤降。
• 确认上拉电阻：DHT22数据引脚需要4.7k-10k的上拉电阻，部分模块自带但可能松动，可额外焊接一个上拉电阻测试。
• 更换传感器测试：DHT22长期运行可能出现元件老化，换全新传感器验证是否仍出现异常。

2. 代码层面修复与优化 #

• 添加异常值过滤：读取温湿度后判断是否为nan，仅在数值有效时上传到Adafruit IO，避免干扰Dashboard。修改后的读取逻辑示例：

  sensors_event_t event;
  dht.temperature().getEvent(&event);
  float celsius = event.temperature;
  
  if (!isnan(celsius)) {
    Serial.print("Celsius: ");
    Serial.print(celsius);
    Serial.println("°C");
    temperature->save(celsius);
  } else {
    Serial.println("温度读取失败");
  }
  
  dht.humidity().getEvent(&event);
  float hum = event.relative_humidity;
  if (!isnan(hum)) {
    Serial.print("Umidade: ");
    Serial.print(hum);
    Serial.println("%");
    humidity->save(hum);
  } else {
    Serial.println("湿度读取失败");
  }
  

• 添加软件看门狗：ESP8266长期运行可能假死，引入软件看门狗定期喂狗，防止系统挂起。
• 延长读取间隔：将当前5秒的读取间隔延长至10秒，减少传感器的工作负荷。

3. 电磁干扰排查 #

• 继电器抗干扰：给继电器线圈并联续流二极管，抑制开关时产生的电磁脉冲，避免干扰DHT22的信号传输。
• 物理隔离：将传感器与继电器模块的布线分开，减少电磁耦合干扰。

内容的提问来源于stack exchange，提问作者Fernando