Compilation error: 'mq2' was not declared in this scope

[nisa6767]

For my IoT project, I'm creating a smoke and gas detector. Although I am using #include <MQUnifiedsensor.h> and also <MQ2.h> in my code, it appears that the readTemperature member of the MQ2 class is missing. Can somebody help me to check the error?

The code:

#define BLYNK_TEMPLATE_ID "xxxxxxxxxxxxxx"
#define BLYNK_DEVICE_NAME "xxxxxxxxxxxxxx"
#define BLYNK_AUTH_TOKEN "xxxxxxxxxxxxxx"

#define BLYNK_PRINT Serial

#include <ESP8266WiFi.h>
#include <BlynkSimpleEsp8266.h>
#include <MQ2.h>

char ssid[] = "xxxxxxxxxxxxxx";
char pass[] ="xxxxxxxxxxxxxx";

BlynkTimer timer;
int pinValue = 0;

#define Buzzer D5
#define Green D6
#define Red D7
#define MQ2PIN A0

float t_threshold = 50.00;
bool alert_sent = false;

void setup() {
Serial.begin(9600);
mq2.begin();
pinMode(Green, OUTPUT);
pinMode(Red, OUTPUT);
pinMode(Buzzer, OUTPUT);

Blynk.begin(BLYNK_AUTH_TOKEN, ssid, pass);
timer.setInterval(1000L, notification);
}

BLYNK_WRITE(V0) {
pinValue = param.asInt();

}

void notification() {
float t = mq2.readTemperature();

if (t > t_threshold && alert_sent == false) {
 digitalWrite(Green, HIGH);
 digitalWrite(Red, LOW);
 digitalWrite(Buzzer, LOW);
 Blynk.logEvent("gas_leak_detected",  String("The temperature is ") +t);
 Serial.println("High temperature alert!");
 Serial.println("Blynk Alert Notification sent!");
 Serial.println();
 alert_sent = true;

 } else if (t <= t_threshold && alert_sent == true) {
   Serial.println("Temperature back to normal");
   Serial.println();
   alert_sent = false;
 }
}

void loop() {
Blynk.run();
timer.run();
}

This is the error:

C:\Users\User\OneDrive\Documents\Arduino\coding-2\coding-2\coding-2.ino: In function 'void setup()':
C:\Users\User\OneDrive\Documents\Arduino\coding-2\coding-2\coding-2.ino:27:3: error: 'mq2' was not declared in this scope
27 | mq2.begin();
| ^~~
C:\Users\User\OneDrive\Documents\Arduino\coding-2\coding-2\coding-2.ino: In function 'void notification()':
C:\Users\User\OneDrive\Documents\Arduino\coding-2\coding-2\coding-2.ino:42:13: error: 'mq2' was not declared in this scope
42 | float t = mq2.readTemperature();
| ^~~

exit status 1

Compilation error: 'mq2' was not declared in this scope

[groundFungus]

You seem to be missing a constructor (to create a MQ2 object).

MQ2 mq2(pin);

See the example
GitHub - labay11/MQ-2-sensor-library: A simple library to retrieve the information given from the MQ 2 sensor in arduino

[nisa6767]

I already try to add the constructor, but there are still have error:

Code:

#define BLYNK_TEMPLATE_ID "xxxxxxxxxxxxxx"
#define BLYNK_DEVICE_NAME "xxxxxxxxxxxxxx"
#define BLYNK_AUTH_TOKEN "xxxxxxxxxxxxxx"

#define BLYNK_PRINT Serial

#include <ESP8266WiFi.h>
#include <BlynkSimpleEsp8266.h>
#include <MQ2.h>

char ssid[] = "xxxxxxxxxxxxxx";
char pass[] ="xxxxxxxxxxxxxx";

BlynkTimer timer;
int pinValue = 0;

#define Buzzer D5
#define Green D6
#define Red D7

float t_threshold = 50.00;
bool alert_sent = false;

MQ2 mq2(A0);

void setup() {
Serial.begin(9600);
mq2.begin();
pinMode(Green, OUTPUT);
pinMode(Red, OUTPUT);
pinMode(Buzzer, OUTPUT);

Blynk.begin(BLYNK_AUTH_TOKEN, ssid, pass);
timer.setInterval(1000L, notification);
}

BLYNK_WRITE(V0) {
pinValue = param.asInt();

}

void notification() {
float t = mq2.readTemperature();

if (t > t_threshold && alert_sent == false) {
 digitalWrite(Green, HIGH);
 digitalWrite(Red, LOW);
 digitalWrite(Buzzer, LOW);
 Blynk.logEvent("gas_leak_detected",  String("The temperature is ") +t);
 Serial.println("High temperature alert!");
 Serial.println("Blynk Alert Notification sent!");
 Serial.println();
 alert_sent = true;

 } else if (t <= t_threshold && alert_sent == true) {
   Serial.println("Temperature back to normal");
   Serial.println();
   alert_sent = false;
 }
}

void loop() {
Blynk.run();
timer.run();
}

The error:

C:\Users\User\OneDrive\Documents\Arduino\coding-2\coding-2\coding-2.ino: In function 'void notification()':
C:\Users\User\OneDrive\Documents\Arduino\coding-2\coding-2\coding-2.ino:43:15: error: 'class MQ2' has no member named 'readTemperature'
   43 | float t = mq2.readTemperature();
      |               ^~~~~~~~~~~~~~~

exit status 1

Compilation error: 'class MQ2' has no member named 'readTemperature'```

[nisa6767]

I think i already fix it. It has no error. I changed from float t = mq2.readTemperature(); to float smoke = mq2.readSmoke();

Is this mq2 sensor can't read the temperature?

This is the new code:

#define BLYNK_TEMPLATE_ID "xxxxxxxxxxx"
#define BLYNK_DEVICE_NAME "xxxxxxxxxxx"
#define BLYNK_AUTH_TOKEN "xxxxxxxxxxx"

#define BLYNK_PRINT Serial

#include <ESP8266WiFi.h>
#include <BlynkSimpleEsp8266.h>
#include <MQ2.h>

char ssid[] = "xxxxxxxxxxx";
char pass[] = "xxxxxxxxxxx";

BlynkTimer timer;
int pinValue = 0;

#define Buzzer D5
#define Green D6
#define Red D7

float smoke_threshold = 50.00;
bool alert_sent = false;

MQ2 mq2(A0);

void setup() {
Serial.begin(9600);
mq2.begin();
pinMode(Green, OUTPUT);
pinMode(Red, OUTPUT);
pinMode(Buzzer, OUTPUT);

Blynk.begin(BLYNK_AUTH_TOKEN, ssid, pass);
timer.setInterval(1000L, notification);
}

BLYNK_WRITE(V0) {
pinValue = param.asInt();

}

void notification() {
float smoke = mq2.readSmoke();

if (smoke > smoke_threshold && alert_sent == false) {
 digitalWrite(Green, HIGH);
 digitalWrite(Red, LOW);
 digitalWrite(Buzzer, LOW);
 Blynk.logEvent("gas_leak_detected",  String("The temperature is ") +smoke);
 Serial.println("High temperature alert!");
 Serial.println("Blynk Alert Notification sent!");
 Serial.println();
 alert_sent = true;

 } else if (smoke <= smoke_threshold && alert_sent == true) {
   Serial.println("Temperature back to normal");
   Serial.println();
   alert_sent = false;
 }
}

void loop() {
Blynk.run();
timer.run();
}

[nisa6767]

I managed to connect to wifi and also to the blynk cloud.
But I can't trigger the gas concentration value. I don't know if there are something wrong with the code or something else because i can verify and compile the code.