Conflicting Declration Error in Using A Lib Twice

hello, my friends. We are trying to assemble a quality monitor, we have assembled the boar₫ itself using mq131, mq135, and dht11, but since it's my first day using Arduino, I can't really code well and I need help, please.

/*
  MQUnifiedsensor Library - reading an MQ135

  Demonstrates the use a MQ135 sensor.
  Library originally added 01 may 2019
  by Miguel A Califa, Yersson Carrillo, Ghiordy Contreras, Mario Rodriguez
 
  Added example
  modified 23 May 2019
  by Miguel Califa 

  Updated library usage
  modified 26 March 2020
  by Miguel Califa 

  Wiring:
  https://github.com/miguel5612/MQSensorsLib_Docs/blob/master/static/img/MQ_Arduino.PNG
  Please make sure arduino A0 pin represents the analog input configured on #define pin

 This example code is in the public domain.

*/

//Include the library
#include <MQUnifiedsensor.h>
#include <MQUnifiedsensor.h>
#include "DHT.h"
#include <MQ131.h>

//Definitions
#define DHTPIN 4 // paye data sensor be 4 arduino vasl shode    
#define DHTTYPE DHT11   // DHT 11
#define placa "Arduino UNO"
#define Voltage_Resolution 5
#define pin A0 //Analog input 0 of your arduino
#define type "MQ-135" //MQ135
#define ADC_Bit_Resolution 10 // For arduino UNO/MEGA/NANO
#define RatioMQ135CleanAir 3.6//RS / R0 = 3.6 ppm  
#define pindng A1
#define typesty "MQ-131"
#define RatioMQ131CleanAir 15
//#define calibration_button 13 //Pin to calibrate your sensor

//Declare Sensor
MQUnifiedsensor MQ131(placa, Voltage_Resolution, ADC_Bit_Resolution, pindng, typesty);

DHT dht(DHTPIN, DHTTYPE);//sakht class
MQUnifiedsensor MQ135(placa, Voltage_Resolution, ADC_Bit_Resolution, pin, type);
void setup() {
  
  //Init the serial port communication - to debug the library
  Serial.begin(9600); //Init serial port
  MQ131.setRegressionMethod(1); //_PPM =  a*ratio^b
  dht.begin();
  //Set math model to calculate the PPM concentration and the value of constants
  MQ135.setRegressionMethod(1); //_PPM =  a*ratio^b  
  /*****************************  MQ Init ********************************************/ 
  //Remarks: Configure the pin of arduino as input.
  /************************************************************************************/ 
  MQ131.init(); 
  MQ135.init(); 

  /* 
    //If the RL value is different from 10K please assign your RL value with the following method:
    MQ135.setRL(10);
  */
  /*****************************  MQ CAlibration ********************************************/ 
  // Explanation: 
  // In this routine the sensor will measure the resistance of the sensor supposedly before being pre-heated
  // and on clean air (Calibration conditions), setting up R0 value.
  // We recomend executing this routine only on setup in laboratory conditions.
  // This routine does not need to be executed on each restart, you can load your R0 value from eeprom.
  // Acknowledgements: https://jayconsystems.com/blog/understanding-a-gas-sensor
  Serial.print("Calibrating please wait.");
  float calcR0 = 0;
  for(int i = 1; i<=10; i ++)
  {
    MQ135.update(); // Update data, the arduino will read the voltage from the analog pin
    calcR0 += MQ135.calibrate(RatioMQ135CleanAir);
    MQ131.update(); // Update data, the arduino will read the voltage from the analog pin
    calcR0 += MQ131.calibrate(RatioMQ131CleanAir);
    Serial.print(".");
  }
  Serial.print("\n");
  MQ135.setR0(calcR0/10);
  MQ131.setR0(calcR0/10);
  
  if(isinf(calcR0)) {Serial.println("Warning: Conection issue, R0 is infinite (Open circuit detected) please check your wiring and supply"); while(1);}
  if(calcR0 == 0){Serial.println("Warning: Conection issue found, R0 is zero (Analog pin shorts to ground) please check your wiring and supply"); while(1);}
  /*****************************  MQ CAlibration ********************************************/
}

void loop() {
  Serial.println("Sampling...");
  MQ135.update(); // Update data, the arduino will read the voltage from the analog pin

  MQ135.setA(605.18); MQ135.setB(-3.937); // Configure the equation to calculate CO concentration value
  float CO = MQ135.readSensor(); // Sensor will read PPM concentration using the model, a and b values set previously or from the setup

  MQ135.setA(77.255); MQ135.setB(-3.18); //Configure the equation to calculate Alcohol concentration value
  float Alcohol = MQ135.readSensor(); // SSensor will read PPM concentration using the model, a and b values set previously or from the setup

  MQ135.setA(110.47); MQ135.setB(-2.862); // Configure the equation to calculate CO2 concentration value
  float CO2 = MQ135.readSensor(); // Sensor will read PPM concentration using the model, a and b values set previously or from the setup

  MQ135.setA(44.947); MQ135.setB(-3.445); // Configure the equation to calculate Toluen concentration value
  float Toluen = MQ135.readSensor(); // Sensor will read PPM concentration using the model, a and b values set previously or from the setup
  
  MQ135.setA(102.2 ); MQ135.setB(-2.473); // Configure the equation to calculate NH4 concentration value
  float NH4 = MQ135.readSensor(); // Sensor will read PPM concentration using the model, a and b values set previously or from the setup

  MQ135.setA(34.668); MQ135.setB(-3.369); // Configure the equation to calculate Aceton concentration value
  float Aceton = MQ135.readSensor(); // Sensor will read PPM concentration using the model, a and b values set previously or from the setup

  MQ131.setA(23.943); MQ131.setB(-1.11);
  MQ131.update(); // Update data, the arduino will read the voltage from the analog pin // Sensor will read PPM concentration using the model, a and b values set previously or from the setup
  float O3 = MQ131.readSensorR0Rs();
  MQ131.setA(-462.43); MQ131.setB(-2.204);
  MQ131.update();
  float NOx = MQ131.readSensorR0Rs();
  MQ131.setA(47.209); MQ131.setB(-1.186);
  MQ131.update();
  float CL2 = MQ131.readSensorR0Rs();
  // Note: 400 Offset for CO2 source: https://github.com/miguel5612/MQSensorsLib/issues/29
  /*
  Motivation:
  We have added 400 PPM because when the library is calibrated it assumes the current state of the
  air as 0 PPM, and it is considered today that the CO2 present in the atmosphere is around 400 PPM.
  https://www.lavanguardia.com/natural/20190514/462242832581/concentracion-dioxido-cabono-co2-atmosfera-bate-record-historia-humanidad.html
  */
  /*
    Exponential regression:
  GAS      | a      | b
  CO       | 605.18 | -3.937  
  Alcohol  | 77.255 | -3.18 
  CO2      | 110.47 | -2.862
  Toluen  | 44.947 | -3.445
  NH4      | 102.2  | -2.473
  Aceton  | 34.668 | -3.369
  */
  float h = dht.readHumidity();
  // Read temperature as Celsius (the default)
  float t = dht.readTemperature();
 
  // Compute heat index in Celsius (isFahreheit = false)
  float hic = dht.computeHeatIndex(t, h, false);
 
  Serial.print("Humidity: ");
  Serial.print(h);
  Serial.print("%");
  Serial.print(" | ");
  Serial.print("Temperature: ");
  Serial.print(t);
  Serial.print(" *C ");
  Serial.print(" | ");
  Serial.print("Heat index: ");
  Serial.print(hic);
  Serial.print(" *C ");
  Serial.print(" | ");
  Serial.print("CO2:");
  Serial.print(CO2+400);
  Serial.print(" PPM");
  Serial.print(" | ");
  Serial.print("CO:");
  Serial.print(CO);
  Serial.print(" | ");
  Serial.print("Alcohol: ");
  Serial.print(Alcohol);
  Serial.print(" PPM");
  Serial.print(" | ");
  Serial.print("Toluen: ");
  Serial.print(Toluen);
  Serial.print(" PPM");
  Serial.print(" | ");
  Serial.print("NH4: ");
  Serial.print(NH4);
  Serial.print(" PPM");
  Serial.print(" | ");
  Serial.print("Aceton: ");
  Serial.print(Aceton);
  Serial.print(" PPM");
  Serial.print(" | ");
  Serial.print("Ozone: ");
  Serial.print(O3);
  Serial.print(" PPM");
  Serial.print(" | ");
  Serial.print("CL2: ");
  Serial.print(CL2);
  Serial.print(" PPM");
  Serial.print(" | ");
  Serial.print("NOx: ");
  Serial.print(NOx);
  Serial.print(" PPM");
  Serial.print(" | ");
  Serial.print("O3: ");
  Serial.print(MQ131.getO3(PPM));
  Serial.println(" PPM");
  Serial.print(" | ");
  Serial.print("O3: ");
  Serial.print(MQ131.getO3(PPB));
  Serial.print(" PPB");
  Serial.print(" | ");
  Serial.print("O3: ");
  Serial.print(MQ131.getO3(MG_M3));
  Serial.print(" mg/m3");
  Serial.print(" | ");
  Serial.print("O3: ");
  Serial.print(MQ131.getO3(UG_M3));
  Serial.print(" ug/m3");
  Serial.print("\n");
  delay(500); //Sampling frequency
}

i get this error

conflicting declaration 'MQUnifiedsensor MQ131'
 MQUnifiedsensor MQ131(placa, Voltage_Resolution, ADC_Bit_Resolution, pindng, typesty);

Welcome

Try remove this line : #include <MQ131.h>

The reason you have this error is because this file MQ131.h contains this line : extern MQ131Class MQ131; so it declared a variable named MQ131, and in your code you try to declare another variable with the same name.

You don't need this library, as you already use another one MQUnifiedsensor

1 Like

Can't I use them both? because one code gives just ozone in ppb , ppm and other things but the mqunified code just gives ppm

and I red other forums , and in that forums people said use namespace

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