ESP32多传感器数据上传ThingSpeak时fireLevel与gasLevel显示0的问题

问题描述 #

使用ESP32 NodeMCU开发板，搭配DHT11、KY-026火焰传感器、MQ-135空气质量传感器。不引入ThingSpeak库时，fireLevel（KY-026）和gasLevel（MQ-135）的analogRead值正常（非0）；但引入ThingSpeak库并连接WiFi上传数据后，这两个值始终显示为0。

核心原因 #

ESP32的WiFi模块会独占ADC2通道进行射频校准，当WiFi处于连接状态时，所有ADC2对应的GPIO引脚无法正常读取模拟值。你的代码中：

• AIRQ_SENSOR定义为GPIO2，属于ADC2_CH2
• FIRE_SENSOR_ANALOG定义为GPIO14，属于ADC2_CH6
  这两个引脚在WiFi启动后被占用，导致analogRead返回0。

解决方案 #

将模拟传感器的接线切换到ESP32的ADC1引脚，ADC1的引脚不受WiFi影响，可在WiFi连接时正常读取模拟值。ESP32的ADC1引脚包括：GPIO32、GPIO33、GPIO34、GPIO35、GPIO36、GPIO39。

修改步骤 #

1. 硬件接线调整：
   • 将MQ-135的模拟输出引脚接到GPIO34
   • 将KY-026的模拟输出引脚接到GPIO35
2. 代码引脚定义修改：

   #define AIRQ_SENSOR 34 // 替换为ADC1引脚GPIO34
   #define FIRE_SENSOR_ANALOG 35 // 替换为ADC1引脚GPIO35
   

额外优化建议 #

• 将WiFi连接逻辑移到setup()函数中，避免每次循环重复执行连接操作，减少资源浪费
• 修正代码中Unhealty的拼写错误为Unhealthy
• 在fireSensor函数中，将全屏清屏改为局部清除位图区域，避免误删其他显示内容

修改后的完整代码 #

#include <WiFi.h>
#include "ThingSpeak.h"
#include <SPI.h>
#include <Wire.h>
#include <DHT.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

const char* ssid = "SECRET_SSID";
const char* password = "SECRET_PASSWORD";

WiFiClient client;

unsigned long channelNum = X;
const char* APIKey = "SECRET_KEY";

// 替换为ADC1引脚
#define AIRQ_SENSOR 34 // ESP32 pin GPIO34 connected to mq135 sensor
#define DHT_SENSOR_PIN  13 // ESP32 pin GIOP13 connected to DHT11 sensor
#define DHT_SENSOR_TYPE DHT11
#define FIRE_SENSOR_ANALOG 35 // ESP32 pin GPIO35 connected to Fire sensor
#define SCREEN_WIDTH 128 // OLED display width, in pixels
#define SCREEN_HEIGHT 64 // OLED display height, in pixels
#define OLED_RESET     4 // Reset pin # (or -1 if sharing Arduino reset pin)

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);
DHT dht_sensor(DHT_SENSOR_PIN, DHT_SENSOR_TYPE);
float humi, tempC, gasLevel, fireLevel;
String quality = "";

const uint8_t bitmap19[] = {0x00, 0x00, 0x00, 0x00, 0x18, 0x00, 0x00, 0x1c, 0x00, 0x00, 0x1c, 0x00, 0x00, 0x1e, 0x00, 0x00, 0x3f, 0x00, 0x00, 0x3f, 0x40, 0x00, 0x7f, 0x60, 0x00, 0xff, 0xe0, 0x00, 0xff, 0xf0, 0x06, 0xff, 0xf0, 0x07, 0xff, 0xf8, 0x07, 0xff, 0xf8, 0x0f, 0xf7, 0xf8, 0x0f, 0xe7, 0xf8, 0x1f, 0xe3, 0xfc, 0x1f, 0xc1, 0xfc, 0x3f, 0x80, 0xfc, 0x3f, 0x80, 0xf8, 0x1f, 0x00, 0xf8, 0x1f, 0x00, 0xf0, 0x0f, 0x00, 0xe0, 0x07, 0x80, 0xc0, 0x01, 0x81, 0x00};

void setup() {
  Serial.begin(9600);
  dht_sensor.begin(); // initialize the DHT sensor
  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3c)) { // Address 0x3D for 128x64
    Serial.println(F("SSD1306 allocation failed"));
  }
  display.clearDisplay();
  display.setTextColor(WHITE);
  
  display.setTextSize(2);
  display.setCursor(50, 0);
  display.println("Air");
  display.setTextSize(1);
  display.setCursor(23, 20);
  display.println("Quality Monitor");
  display.display();
  delay(1200);
  display.clearDisplay();

  // WiFi连接移到setup执行一次
  WiFi.mode(WIFI_STA);
  Serial.print("Attempting to connect to SSID: ");
  Serial.println(ssid);
  while(WiFi.status() != WL_CONNECTED){
    WiFi.begin(ssid, password);
    Serial.print(".");
    delay(5000);     
  } 
  Serial.println("\nConnected.");
  
  ThingSpeak.begin(client);
}

void fireSensor() {
  fireLevel = analogRead(FIRE_SENSOR_ANALOG);
  Serial.println("fire level: " + String(fireLevel));
  if(fireLevel < 2000) {
    display.drawBitmap(90, 35, bitmap19, 24, 24, 1);
  }
  else {
    // 仅清除位图区域，保留其他显示内容
    display.fillRect(90, 35, 24, 24, BLACK);
  }
}

void temphSensor() {
  // read humidity
  humi  = dht_sensor.readHumidity();
  // read temperature in Celsius
  tempC = dht_sensor.readTemperature();

  // check whether the reading is successful or not
  if ( isnan(tempC) || isnan(humi)) {
    Serial.println("Failed to read from DHT sensor!");
  } else {
    display.setTextColor(WHITE);
    display.setTextSize(1);
    display.setCursor(0, 35);
    display.println("Tmp:");
    display.setCursor(30, 35);
    display.println(tempC);
    display.setCursor(64, 35);
    display.println("C");
    display.setCursor(0, 50);
    display.println("RH:");
    display.setCursor(30, 50);
    display.println(humi);
    display.setCursor(64, 50);
    display.println("%");
  }
}

void airqSensor() {
  gasLevel = analogRead(AIRQ_SENSOR);

  Serial.println("gas Level: " + String(gasLevel));
  if(gasLevel < 500) {
    quality = "Good";
  }
  else if(gasLevel < 750) {
    // avg 750
    quality = "Moderate";
  }
  else if(gasLevel < 1500) {
    // avg 1500
    quality = "Unhealthy"; // 修正拼写错误
  }
  else {
    // 2000 >
    quality = "Hazardous";
  }

  display.setTextColor(WHITE);
  display.setTextSize(1);
  display.setCursor(30, 5);
  display.println("Air Quality");
  display.setCursor(35, 20);
  display.println(quality);
}

void writeThingSpeak() {
  ThingSpeak.setField(1, tempC);
  ThingSpeak.setField(2, humi);
  ThingSpeak.setField(3, gasLevel);
  ThingSpeak.setField(4, fireLevel);

  int x = ThingSpeak.writeFields(channelNum, APIKey);

  if(x == 200) {
    Serial.println("Channel update successful.");
  }
  else {
    Serial.println("Problem updating channel. HTTP error code " + String(x));
  }
  delay(15000);
}

void loop() {
  display.clearDisplay();

  fireSensor();
  airqSensor();
  temphSensor();
  display.display();
  writeThingSpeak();
}

内容的提问来源于stack exchange，提问作者dizzyme09