arduino 传感器在 wifi 上的故障

Question

I have an esp32 firmware that uses 4 sensors (DHT11, PIR, water leakage, MQ2). All sensors work fine and give accurate output but when I try to include Wi-Fi connection and Wi-Fi client the water and mq2 sensors give wrong and random data. Is there anybody who experienced this issue before?

Here is an example of the output without Wi-Fi:

• temperature: 18
• humidity: 58
• water level: 97
• motion: 1
• smoke: 6
• LPG: 12
• CO: 8

and with the Wi-Fi commands it shows like this:

• temperature: 18
• humidity: 58
• water level: 4065
• motion: 1
• smoke: 26145582395.16
• LPG: 26145582395.16
• CO: 26145582395.16

and here is the code used:

#include <DHTesp.h>
#include <WiFi.h>
#include <MQ2.h>

#ifndef ESP32
#pragma message(THIS EXAMPLE IS FOR ESP32 ONLY!)
#error Select ESP32 board.
#endif

const char* ssid = "Mynetwork";
const char* password = "********";

const uint16_t port = 8090;
const char * host = "***********";

const int dhtPin = 18;
const int waterPin = 26;
const int mq2Pin   = 2;
const int pirPin = 25;

int factor=0;

DHTesp dht;
MQ2 mq2(mq2Pin);

void setup() {


  pinMode(pirPin,INPUT);
  pinMode(waterPin,INPUT);
  pinMode(mq2Pin,INPUT);
  pinMode(pirPin,INPUT);


  Serial.begin(115200);
  mq2.begin();
  dht.setup(dhtPin, DHTesp::DHT11);
  factor = analogRead(waterPin);

  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
  delay(2000);
  Serial.println("...");

  }


}

void loop() {

  WiFiClient client;

  if (!client.connect(host, port)) {

        Serial.println("Connection to host failed");

        delay(500);
        return;
    }

    Serial.print("WiFi connected with IP: ");
    Serial.println(WiFi.localIP());


    float *values= mq2.read(true);


    Serial.print("Temperature:\t");
  Serial.println(getTemp());
    client.println(getTemp());

    Serial.print("Humidity:\t");
  Serial.println(getHum());
    client.println(getHum());

    Serial.print("movement:\t");
    Serial.println(getPir());
    client.println(getPir());

    Serial.print("Water state:\t");
  Serial.println(getWater());
    client.println(getWater());

    Serial.print("LPG:\t");
  Serial.println(getLPG());
    client.println(getLPG());

    Serial.print("Smoke:\t");
  Serial.println(getSmoke());
    client.println(getSmoke());

   Serial.print("CO:\t");
  Serial.println(getCO());
   client.println(getCO());

  delay(3000);


}
float getTemp(){
  return dht.getTemperature();
}
float getHum(){
  return dht.getHumidity();
}
int getWater(){
   int sensorValue = analogRead(waterPin)-factor;  
   int per= (sensorValue*100/4094);
   return map(per,0,33,0,100);
}


float getSmoke(){
  return mq2.smoke;
}
float getLPG(){     
  return mq2.lpg;
}
float getCO(){
  return mq2.co;
}
int getPir(){
  return (digitalRead(pirPin));
}

Answer 1

ESP32 internally has two ADCs, but ADC2 is shared between other resources within ESP32. They are mapped as:

ADC1_CH0 -- GPIO36
ADC1_CH1 -- Not available on some ESP32 development board
ADC1_CH2 -- NA
ADC1_CH3 -- GPIO39
ADC1_CH6 -- GPIO34
ADC1_CH7 -- GPIO35
ADC1_CH4 -- GPIO32
ADC1_CH5 -- GPIO33

ADC2_CH0 --- GPIO0
ADC2_CH1 --- Not available on some boards
ADC2_CH2 --- GPIO2
ADC2_CH3 --- GPIO15
ADC2_CH4 --- GPIO13
ADC2_CH5 --- GPIO12
ADC2_CH6 --- GPIO14
ADC2_CH7 --- GPIO27
ADC2_CH8 --- GPIO25
ADC2_CH9 --- GPIO26

ADC2 pins can not be used when WiFi is used. On the other hand, ADC1 pins can be used even when WiFi is enabled. Source of reference .

Therefore, instead of using pin2 for your MQ sensor, try to use pin 36 or 34.

Also ESP32 is well-known for its noise, try to add a 10uF and 0.1uF capacitors between 3v3 and GND.

One more thing you need to aware if you are planning to use ESP32 for your analog measurement in your project that ESP32 ADCs are not linear, I have a blog talk about the non-linearity of ESP32 ADC and how I use uses a Look-up table to correct the non-linearity .