Arduino And MQ2 Gas Sensor

The Grove Gas Sensor (MQ2) module is useful for gas leakage detection (home and industry). It is suitable for detecting H2, LPG, CH4 and CO.

Mar 16, 2018

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environmental sensing

Components and supplies

Arduino UNO

MQ 2 Gas Sensor

USB Cable 2.0 Type A/B for Arduino Uno

Breadboard

Jumper Wires

Prototype Expansion Board for Arduino Uno

Project description

Code

Arduino Code

arduino

https://plus.google.com/u/0/+MahamudulKarimKhondaker/posts/HYGPcEFVdBe

1
2#define         MQ_PIN                       (0)     //define which   analog input channel you are going to use
3#define         RL_VALUE                     (5)      //define the load resistance on the board, in kilo ohms
4#define         RO_CLEAN_AIR_FACTOR           (9.83)  //RO_CLEAR_AIR_FACTOR=(Sensor resistance in clean air)/RO,
5                                                      //which is derived from the   chart in datasheet
6 
7/**********************Software Related Macros***********************************/
8#define          CALIBARAION_SAMPLE_TIMES     (50)    //define how many samples you are   going to take in the calibration phase
9#define         CALIBRATION_SAMPLE_INTERVAL   (500)   //define the time interal(in milisecond) between each samples in the
10                                                      //cablibration phase
11#define          READ_SAMPLE_INTERVAL         (50)    //define how many samples you are   going to take in normal operation
12#define         READ_SAMPLE_TIMES            (5)      //define the time interal(in milisecond) between each samples in 
13#include   <LiquidCrystal.h>
14
15const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7   = 2;
16LiquidCrystal lcd(rs, en, d4, d5, d6, d7);                                                     //normal   operation
17 
18/*********************Application Related Macros*********************************/
19#define          GAS_LPG                      (0)
20#define         GAS_CO                       (1)
21#define          GAS_SMOKE                    (2)
22 
23/****************************Globals**********************************************/
24float            LPGCurve[3]  =  {2.3,0.21,-0.47};   //two points are taken from the curve.   
25                                                    //with these two points,   a line is formed which is "approximately equivalent"
26                                                    //to   the original curve. 
27                                                    //data   format:{ x, y, slope}; point1: (lg200, 0.21), point2: (lg10000, -0.59) 
28float            COCurve[3]  =  {2.3,0.72,-0.34};    //two points are taken from the curve.   
29                                                    //with these two points,   a line is formed which is "approximately equivalent" 
30                                                    //to   the original curve.
31                                                    //data   format:{ x, y, slope}; point1: (lg200, 0.72), point2: (lg10000,  0.15) 
32float            SmokeCurve[3] ={2.3,0.53,-0.44};    //two points are taken from the curve.   
33                                                    //with these two points,   a line is formed which is "approximately equivalent" 
34                                                    //to   the original curve.
35                                                    //data   format:{ x, y, slope}; point1: (lg200, 0.53), point2: (lg10000,  -0.22)                                                     
36float            Ro           =  10;                 //Ro is initialized to 10 kilo ohms
37   
38void setup()
39{
40  Serial.begin(9600);                               //UART   setup, baudrate = 9600bps
41  Serial.print("Calibrating...\
42");                
43   Ro = MQCalibration(MQ_PIN);                       //Calibrating the sensor. Please   make sure the sensor is in clean air 
44   lcd.begin(16, 2);                                                  //when   you perform the calibration                    
45  Serial.print("Calibration   is done...\
46"); 
47  Serial.print("Ro=");
48  Serial.print(Ro);
49  Serial.print("kohm");
50   Serial.print("\
51");
52lcd.print("Calibration is done...\
53"); 
54lcd.print("Ro=");
55lcd.print(Ro);
56lcd.print("kohm");
57lcd.print("\
58");
59}
60   
61void loop()
62{
63   Serial.print("LPG:"); 
64   Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_LPG)   );
65   Serial.print( "ppm" );
66   Serial.print("    ");   
67   Serial.print("CO:");   
68   Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_CO) );
69   Serial.print(   "ppm" );
70   Serial.print("    ");   
71   Serial.print("SMOKE:"); 
72    Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_SMOKE) );
73   Serial.print(   "ppm" );
74   Serial.print("\
75");
76        lcd.setCursor(0, 0);
77        lcd.print("LPG:");
78lcd.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_LPG)   );
79//lcd.print( "ppm" );
80lcd.print("     ");  
81  lcd.setCursor(9, 0);
82lcd.print("CO:");   
83lcd.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_CO) );
84//lcd.print( "ppm"   );
85lcd.print("       "); 
86 lcd.setCursor(0, 1);  
87lcd.print("SMOKE:");   
88lcd.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_SMOKE) );
89//lcd.print(   "ppm" );
90lcd.print("         ");
91   delay(200);
92}
93 
94/****************   MQResistanceCalculation **************************************
95Input:   raw_adc   - raw value read from adc, which represents the voltage
96Output:  the calculated   sensor resistance
97Remarks: The sensor and the load resistor forms a voltage divider.   Given the voltage
98         across the load resistor and its resistance, the resistance   of the sensor
99         could be derived.
100**********************************************************************************/   
101float MQResistanceCalculation(int raw_adc)
102{
103  return ( ((float)RL_VALUE*(1023-raw_adc)/raw_adc));
104}
105   
106/*************************** MQCalibration **************************************
107Input:    mq_pin - analog channel
108Output:  Ro of the sensor
109Remarks: This function   assumes that the sensor is in clean air. It use  
110         MQResistanceCalculation   to calculates the sensor resistance in clean air 
111         and then divides it   with RO_CLEAN_AIR_FACTOR. RO_CLEAN_AIR_FACTOR is about 
112         10, which differs   slightly between different sensors.
113**********************************************************************************/   
114float MQCalibration(int mq_pin)
115{
116  int i;
117  float val=0;
118 
119   for (i=0;i<CALIBARAION_SAMPLE_TIMES;i++) {            //take multiple samples
120     val += MQResistanceCalculation(analogRead(mq_pin));
121    delay(CALIBRATION_SAMPLE_INTERVAL);
122   }
123  val = val/CALIBARAION_SAMPLE_TIMES;                   //calculate the average   value
124 
125  val = val/RO_CLEAN_AIR_FACTOR;                        //divided   by RO_CLEAN_AIR_FACTOR yields the Ro 
126                                                        //according   to the chart in the datasheet 
127 
128  return val; 
129}
130/***************************   MQRead *******************************************
131Input:   mq_pin - analog   channel
132Output:  Rs of the sensor
133Remarks: This function use MQResistanceCalculation   to caculate the sensor resistenc (Rs).
134         The Rs changes as the sensor   is in the different consentration of the target
135         gas. The sample times   and the time interval between samples could be configured
136         by changing   the definition of the macros.
137**********************************************************************************/   
138float MQRead(int mq_pin)
139{
140  int i;
141  float rs=0;
142 
143  for (i=0;i<READ_SAMPLE_TIMES;i++)   {
144    rs += MQResistanceCalculation(analogRead(mq_pin));
145    delay(READ_SAMPLE_INTERVAL);
146   }
147 
148  rs = rs/READ_SAMPLE_TIMES;
149 
150  return rs;  
151}
152 
153/***************************   MQGetGasPercentage ********************************
154Input:   rs_ro_ratio -   Rs divided by Ro
155         gas_id      - target gas type
156Output:  ppm of the   target gas
157Remarks: This function passes different curves to the MQGetPercentage   function which 
158         calculates the ppm (parts per million) of the target   gas.
159**********************************************************************************/   
160int MQGetGasPercentage(float rs_ro_ratio, int gas_id)
161{
162  if ( gas_id   == GAS_LPG ) {
163     return MQGetPercentage(rs_ro_ratio,LPGCurve);
164  } else   if ( gas_id == GAS_CO ) {
165     return MQGetPercentage(rs_ro_ratio,COCurve);
166   } else if ( gas_id == GAS_SMOKE ) {
167     return MQGetPercentage(rs_ro_ratio,SmokeCurve);
168   }    
169 
170  return 0;
171}
172 
173/***************************  MQGetPercentage   ********************************
174Input:   rs_ro_ratio - Rs divided by Ro
175          pcurve      - pointer to the curve of the target gas
176Output:  ppm of   the target gas
177Remarks: By using the slope and a point of the line. The x(logarithmic   value of ppm) 
178         of the line could be derived if y(rs_ro_ratio) is provided.   As it is a 
179         logarithmic coordinate, power of 10 is used to convert the   result to non-logarithmic 
180         value.
181**********************************************************************************/   
182int  MQGetPercentage(float rs_ro_ratio, float *pcurve)
183{
184  return (pow(10,(   ((log(rs_ro_ratio)-pcurve[1])/pcurve[2]) + pcurve[0])));
185}
186

#define         MQ_PIN                       (0)     //define which   analog input channel you are going to use
#define         RL_VALUE                     (5)      //define the load resistance on the board, in kilo ohms
#define         RO_CLEAN_AIR_FACTOR           (9.83)  //RO_CLEAR_AIR_FACTOR=(Sensor resistance in clean air)/RO,
                                                      //which is derived from the   chart in datasheet
 
/**********************Software Related Macros***********************************/
#define          CALIBARAION_SAMPLE_TIMES     (50)    //define how many samples you are   going to take in the calibration phase
#define         CALIBRATION_SAMPLE_INTERVAL   (500)   //define the time interal(in milisecond) between each samples in the
                                                      //cablibration phase
#define          READ_SAMPLE_INTERVAL         (50)    //define how many samples you are   going to take in normal operation
#define         READ_SAMPLE_TIMES            (5)      //define the time interal(in milisecond) between each samples in 
#include   <LiquidCrystal.h>

const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7   = 2;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);                                                     //normal   operation
 
/*********************Application Related Macros*********************************/
#define          GAS_LPG                      (0)
#define         GAS_CO                       (1)
#define          GAS_SMOKE                    (2)
 
/****************************Globals**********************************************/
float            LPGCurve[3]  =  {2.3,0.21,-0.47};   //two points are taken from the curve.   
                                                    //with these two points,   a line is formed which is "approximately equivalent"
                                                    //to   the original curve. 
                                                    //data   format:{ x, y, slope}; point1: (lg200, 0.21), point2: (lg10000, -0.59) 
float            COCurve[3]  =  {2.3,0.72,-0.34};    //two points are taken from the curve.   
                                                    //with these two points,   a line is formed which is "approximately equivalent" 
                                                    //to   the original curve.
                                                    //data   format:{ x, y, slope}; point1: (lg200, 0.72), point2: (lg10000,  0.15) 
float            SmokeCurve[3] ={2.3,0.53,-0.44};    //two points are taken from the curve.   
                                                    //with these two points,   a line is formed which is "approximately equivalent" 
                                                    //to   the original curve.
                                                    //data   format:{ x, y, slope}; point1: (lg200, 0.53), point2: (lg10000,  -0.22)                                                     
float            Ro           =  10;                 //Ro is initialized to 10 kilo ohms
   
void setup()
{
  Serial.begin(9600);                               //UART   setup, baudrate = 9600bps
  Serial.print("Calibrating...\
");                
   Ro = MQCalibration(MQ_PIN);                       //Calibrating the sensor. Please   make sure the sensor is in clean air 
   lcd.begin(16, 2);                                                  //when   you perform the calibration                    
  Serial.print("Calibration   is done...\
"); 
  Serial.print("Ro=");
  Serial.print(Ro);
  Serial.print("kohm");
   Serial.print("\
");
lcd.print("Calibration is done...\
"); 
lcd.print("Ro=");
lcd.print(Ro);
lcd.print("kohm");
lcd.print("\
");
}
   
void loop()
{
   Serial.print("LPG:"); 
   Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_LPG)   );
   Serial.print( "ppm" );
   Serial.print("    ");   
   Serial.print("CO:");   
   Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_CO) );
   Serial.print(   "ppm" );
   Serial.print("    ");   
   Serial.print("SMOKE:"); 
    Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_SMOKE) );
   Serial.print(   "ppm" );
   Serial.print("\
");
        lcd.setCursor(0, 0);
        lcd.print("LPG:");
lcd.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_LPG)   );
//lcd.print( "ppm" );
lcd.print("     ");  
  lcd.setCursor(9, 0);
lcd.print("CO:");   
lcd.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_CO) );
//lcd.print( "ppm"   );
lcd.print("       "); 
 lcd.setCursor(0, 1);  
lcd.print("SMOKE:");   
lcd.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_SMOKE) );
//lcd.print(   "ppm" );
lcd.print("         ");
   delay(200);
}
 
/****************   MQResistanceCalculation **************************************
Input:   raw_adc   - raw value read from adc, which represents the voltage
Output:  the calculated   sensor resistance
Remarks: The sensor and the load resistor forms a voltage divider.   Given the voltage
         across the load resistor and its resistance, the resistance   of the sensor
         could be derived.
**********************************************************************************/   
float MQResistanceCalculation(int raw_adc)
{
  return ( ((float)RL_VALUE*(1023-raw_adc)/raw_adc));
}
   
/*************************** MQCalibration **************************************
Input:    mq_pin - analog channel
Output:  Ro of the sensor
Remarks: This function   assumes that the sensor is in clean air. It use  
         MQResistanceCalculation   to calculates the sensor resistance in clean air 
         and then divides it   with RO_CLEAN_AIR_FACTOR. RO_CLEAN_AIR_FACTOR is about 
         10, which differs   slightly between different sensors.
**********************************************************************************/   
float MQCalibration(int mq_pin)
{
  int i;
  float val=0;
 
   for (i=0;i<CALIBARAION_SAMPLE_TIMES;i++) {            //take multiple samples
     val += MQResistanceCalculation(analogRead(mq_pin));
    delay(CALIBRATION_SAMPLE_INTERVAL);
   }
  val = val/CALIBARAION_SAMPLE_TIMES;                   //calculate the average   value
 
  val = val/RO_CLEAN_AIR_FACTOR;                        //divided   by RO_CLEAN_AIR_FACTOR yields the Ro 
                                                        //according   to the chart in the datasheet 
 
  return val; 
}
/***************************   MQRead *******************************************
Input:   mq_pin - analog   channel
Output:  Rs of the sensor
Remarks: This function use MQResistanceCalculation   to caculate the sensor resistenc (Rs).
         The Rs changes as the sensor   is in the different consentration of the target
         gas. The sample times   and the time interval between samples could be configured
         by changing   the definition of the macros.
**********************************************************************************/   
float MQRead(int mq_pin)
{
  int i;
  float rs=0;
 
  for (i=0;i<READ_SAMPLE_TIMES;i++)   {
    rs += MQResistanceCalculation(analogRead(mq_pin));
    delay(READ_SAMPLE_INTERVAL);
   }
 
  rs = rs/READ_SAMPLE_TIMES;
 
  return rs;  
}
 
/***************************   MQGetGasPercentage ********************************
Input:   rs_ro_ratio -   Rs divided by Ro
         gas_id      - target gas type
Output:  ppm of the   target gas
Remarks: This function passes different curves to the MQGetPercentage   function which 
         calculates the ppm (parts per million) of the target   gas.
**********************************************************************************/   
int MQGetGasPercentage(float rs_ro_ratio, int gas_id)
{
  if ( gas_id   == GAS_LPG ) {
     return MQGetPercentage(rs_ro_ratio,LPGCurve);
  } else   if ( gas_id == GAS_CO ) {
     return MQGetPercentage(rs_ro_ratio,COCurve);
   } else if ( gas_id == GAS_SMOKE ) {
     return MQGetPercentage(rs_ro_ratio,SmokeCurve);
   }    
 
  return 0;
}
 
/***************************  MQGetPercentage   ********************************
Input:   rs_ro_ratio - Rs divided by Ro
          pcurve      - pointer to the curve of the target gas
Output:  ppm of   the target gas
Remarks: By using the slope and a point of the line. The x(logarithmic   value of ppm) 
         of the line could be derived if y(rs_ro_ratio) is provided.   As it is a 
         logarithmic coordinate, power of 10 is used to convert the   result to non-logarithmic 
         value.
**********************************************************************************/   
int  MQGetPercentage(float rs_ro_ratio, float *pcurve)
{
  return (pow(10,(   ((log(rs_ro_ratio)-pcurve[1])/pcurve[2]) + pcurve[0])));
}

Arduino Code

arduino

https://plus.google.com/u/0/+MahamudulKarimKhondaker/posts/HYGPcEFVdBe

1
2#define         MQ_PIN                       (0)     //define which  analog input channel you are going to use
3#define         RL_VALUE                     (5)     //define the load resistance on the board, in kilo ohms
4#define         RO_CLEAN_AIR_FACTOR          (9.83)  //RO_CLEAR_AIR_FACTOR=(Sensor resistance in clean air)/RO,
5                                                     //which is derived from the  chart in datasheet
6 
7/**********************Software Related Macros***********************************/
8#define         CALIBARAION_SAMPLE_TIMES     (50)    //define how many samples you are  going to take in the calibration phase
9#define         CALIBRATION_SAMPLE_INTERVAL  (500)   //define the time interal(in milisecond) between each samples in the
10                                                     //cablibration phase
11#define         READ_SAMPLE_INTERVAL         (50)    //define how many samples you are  going to take in normal operation
12#define         READ_SAMPLE_TIMES            (5)     //define the time interal(in milisecond) between each samples in 
13#include  <LiquidCrystal.h>
14
15const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7  = 2;
16LiquidCrystal lcd(rs, en, d4, d5, d6, d7);                                                     //normal  operation
17 
18/*********************Application Related Macros*********************************/
19#define         GAS_LPG                      (0)
20#define         GAS_CO                       (1)
21#define         GAS_SMOKE                    (2)
22 
23/****************************Globals**********************************************/
24float           LPGCurve[3]  =  {2.3,0.21,-0.47};   //two points are taken from the curve.  
25                                                    //with these two points,  a line is formed which is "approximately equivalent"
26                                                    //to  the original curve. 
27                                                    //data  format:{ x, y, slope}; point1: (lg200, 0.21), point2: (lg10000, -0.59) 
28float           COCurve[3]  =  {2.3,0.72,-0.34};    //two points are taken from the curve.  
29                                                    //with these two points,  a line is formed which is "approximately equivalent" 
30                                                    //to  the original curve.
31                                                    //data  format:{ x, y, slope}; point1: (lg200, 0.72), point2: (lg10000,  0.15) 
32float           SmokeCurve[3] ={2.3,0.53,-0.44};    //two points are taken from the curve.  
33                                                    //with these two points,  a line is formed which is "approximately equivalent" 
34                                                    //to  the original curve.
35                                                    //data  format:{ x, y, slope}; point1: (lg200, 0.53), point2: (lg10000,  -0.22)                                                     
36float           Ro           =  10;                 //Ro is initialized to 10 kilo ohms
37  
38void setup()
39{
40  Serial.begin(9600);                               //UART  setup, baudrate = 9600bps
41  Serial.print("Calibrating...\
42");                
43  Ro = MQCalibration(MQ_PIN);                       //Calibrating the sensor. Please  make sure the sensor is in clean air 
44   lcd.begin(16, 2);                                                  //when  you perform the calibration                    
45  Serial.print("Calibration  is done...\
46"); 
47  Serial.print("Ro=");
48  Serial.print(Ro);
49  Serial.print("kohm");
50  Serial.print("\
51");
52lcd.print("Calibration is done...\
53"); 
54lcd.print("Ro=");
55lcd.print(Ro);
56lcd.print("kohm");
57lcd.print("\
58");
59}
60  
61void loop()
62{
63   Serial.print("LPG:"); 
64   Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_LPG)  );
65   Serial.print( "ppm" );
66   Serial.print("    ");   
67   Serial.print("CO:");  
68   Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_CO) );
69   Serial.print(  "ppm" );
70   Serial.print("    ");   
71   Serial.print("SMOKE:"); 
72   Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_SMOKE) );
73   Serial.print(  "ppm" );
74   Serial.print("\
75");
76        lcd.setCursor(0, 0);
77        lcd.print("LPG:");
78lcd.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_LPG)  );
79//lcd.print( "ppm" );
80lcd.print("     ");  
81  lcd.setCursor(9, 0);
82lcd.print("CO:");  
83lcd.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_CO) );
84//lcd.print( "ppm"  );
85lcd.print("       "); 
86 lcd.setCursor(0, 1);  
87lcd.print("SMOKE:");  
88lcd.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_SMOKE) );
89//lcd.print(  "ppm" );
90lcd.print("         ");
91   delay(200);
92}
93 
94/****************  MQResistanceCalculation **************************************
95Input:   raw_adc  - raw value read from adc, which represents the voltage
96Output:  the calculated  sensor resistance
97Remarks: The sensor and the load resistor forms a voltage divider.  Given the voltage
98         across the load resistor and its resistance, the resistance  of the sensor
99         could be derived.
100**********************************************************************************/  
101float MQResistanceCalculation(int raw_adc)
102{
103  return ( ((float)RL_VALUE*(1023-raw_adc)/raw_adc));
104}
105  
106/*************************** MQCalibration **************************************
107Input:   mq_pin - analog channel
108Output:  Ro of the sensor
109Remarks: This function  assumes that the sensor is in clean air. It use  
110         MQResistanceCalculation  to calculates the sensor resistance in clean air 
111         and then divides it  with RO_CLEAN_AIR_FACTOR. RO_CLEAN_AIR_FACTOR is about 
112         10, which differs  slightly between different sensors.
113**********************************************************************************/  
114float MQCalibration(int mq_pin)
115{
116  int i;
117  float val=0;
118 
119  for (i=0;i<CALIBARAION_SAMPLE_TIMES;i++) {            //take multiple samples
120    val += MQResistanceCalculation(analogRead(mq_pin));
121    delay(CALIBRATION_SAMPLE_INTERVAL);
122  }
123  val = val/CALIBARAION_SAMPLE_TIMES;                   //calculate the average  value
124 
125  val = val/RO_CLEAN_AIR_FACTOR;                        //divided  by RO_CLEAN_AIR_FACTOR yields the Ro 
126                                                        //according  to the chart in the datasheet 
127 
128  return val; 
129}
130/***************************  MQRead *******************************************
131Input:   mq_pin - analog  channel
132Output:  Rs of the sensor
133Remarks: This function use MQResistanceCalculation  to caculate the sensor resistenc (Rs).
134         The Rs changes as the sensor  is in the different consentration of the target
135         gas. The sample times  and the time interval between samples could be configured
136         by changing  the definition of the macros.
137**********************************************************************************/  
138float MQRead(int mq_pin)
139{
140  int i;
141  float rs=0;
142 
143  for (i=0;i<READ_SAMPLE_TIMES;i++)  {
144    rs += MQResistanceCalculation(analogRead(mq_pin));
145    delay(READ_SAMPLE_INTERVAL);
146  }
147 
148  rs = rs/READ_SAMPLE_TIMES;
149 
150  return rs;  
151}
152 
153/***************************  MQGetGasPercentage ********************************
154Input:   rs_ro_ratio -  Rs divided by Ro
155         gas_id      - target gas type
156Output:  ppm of the  target gas
157Remarks: This function passes different curves to the MQGetPercentage  function which 
158         calculates the ppm (parts per million) of the target  gas.
159**********************************************************************************/  
160int MQGetGasPercentage(float rs_ro_ratio, int gas_id)
161{
162  if ( gas_id  == GAS_LPG ) {
163     return MQGetPercentage(rs_ro_ratio,LPGCurve);
164  } else  if ( gas_id == GAS_CO ) {
165     return MQGetPercentage(rs_ro_ratio,COCurve);
166  } else if ( gas_id == GAS_SMOKE ) {
167     return MQGetPercentage(rs_ro_ratio,SmokeCurve);
168  }    
169 
170  return 0;
171}
172 
173/***************************  MQGetPercentage  ********************************
174Input:   rs_ro_ratio - Rs divided by Ro
175         pcurve      - pointer to the curve of the target gas
176Output:  ppm of  the target gas
177Remarks: By using the slope and a point of the line. The x(logarithmic  value of ppm) 
178         of the line could be derived if y(rs_ro_ratio) is provided.  As it is a 
179         logarithmic coordinate, power of 10 is used to convert the  result to non-logarithmic 
180         value.
181**********************************************************************************/  
182int  MQGetPercentage(float rs_ro_ratio, float *pcurve)
183{
184  return (pow(10,(  ((log(rs_ro_ratio)-pcurve[1])/pcurve[2]) + pcurve[0])));
185}
186

#define         MQ_PIN                       (0)     //define which  analog input channel you are going to use
#define         RL_VALUE                     (5)     //define the load resistance on the board, in kilo ohms
#define         RO_CLEAN_AIR_FACTOR          (9.83)  //RO_CLEAR_AIR_FACTOR=(Sensor resistance in clean air)/RO,
                                                     //which is derived from the  chart in datasheet
 
/**********************Software Related Macros***********************************/
#define         CALIBARAION_SAMPLE_TIMES     (50)    //define how many samples you are  going to take in the calibration phase
#define         CALIBRATION_SAMPLE_INTERVAL  (500)   //define the time interal(in milisecond) between each samples in the
                                                     //cablibration phase
#define         READ_SAMPLE_INTERVAL         (50)    //define how many samples you are  going to take in normal operation
#define         READ_SAMPLE_TIMES            (5)     //define the time interal(in milisecond) between each samples in 
#include  <LiquidCrystal.h>

const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7  = 2;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);                                                     //normal  operation
 
/*********************Application Related Macros*********************************/
#define         GAS_LPG                      (0)
#define         GAS_CO                       (1)
#define         GAS_SMOKE                    (2)
 
/****************************Globals**********************************************/
float           LPGCurve[3]  =  {2.3,0.21,-0.47};   //two points are taken from the curve.  
                                                    //with these two points,  a line is formed which is "approximately equivalent"
                                                    //to  the original curve. 
                                                    //data  format:{ x, y, slope}; point1: (lg200, 0.21), point2: (lg10000, -0.59) 
float           COCurve[3]  =  {2.3,0.72,-0.34};    //two points are taken from the curve.  
                                                    //with these two points,  a line is formed which is "approximately equivalent" 
                                                    //to  the original curve.
                                                    //data  format:{ x, y, slope}; point1: (lg200, 0.72), point2: (lg10000,  0.15) 
float           SmokeCurve[3] ={2.3,0.53,-0.44};    //two points are taken from the curve.  
                                                    //with these two points,  a line is formed which is "approximately equivalent" 
                                                    //to  the original curve.
                                                    //data  format:{ x, y, slope}; point1: (lg200, 0.53), point2: (lg10000,  -0.22)                                                     
float           Ro           =  10;                 //Ro is initialized to 10 kilo ohms
  
void setup()
{
  Serial.begin(9600);                               //UART  setup, baudrate = 9600bps
  Serial.print("Calibrating...\
");                
  Ro = MQCalibration(MQ_PIN);                       //Calibrating the sensor. Please  make sure the sensor is in clean air 
   lcd.begin(16, 2);                                                  //when  you perform the calibration                    
  Serial.print("Calibration  is done...\
"); 
  Serial.print("Ro=");
  Serial.print(Ro);
  Serial.print("kohm");
  Serial.print("\
");
lcd.print("Calibration is done...\
"); 
lcd.print("Ro=");
lcd.print(Ro);
lcd.print("kohm");
lcd.print("\
");
}
  
void loop()
{
   Serial.print("LPG:"); 
   Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_LPG)  );
   Serial.print( "ppm" );
   Serial.print("    ");   
   Serial.print("CO:");  
   Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_CO) );
   Serial.print(  "ppm" );
   Serial.print("    ");   
   Serial.print("SMOKE:"); 
   Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_SMOKE) );
   Serial.print(  "ppm" );
   Serial.print("\
");
        lcd.setCursor(0, 0);
        lcd.print("LPG:");
lcd.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_LPG)  );
//lcd.print( "ppm" );
lcd.print("     ");  
  lcd.setCursor(9, 0);
lcd.print("CO:");  
lcd.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_CO) );
//lcd.print( "ppm"  );
lcd.print("       "); 
 lcd.setCursor(0, 1);  
lcd.print("SMOKE:");  
lcd.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_SMOKE) );
//lcd.print(  "ppm" );
lcd.print("         ");
   delay(200);
}
 
/****************  MQResistanceCalculation **************************************
Input:   raw_adc  - raw value read from adc, which represents the voltage
Output:  the calculated  sensor resistance
Remarks: The sensor and the load resistor forms a voltage divider.  Given the voltage
         across the load resistor and its resistance, the resistance  of the sensor
         could be derived.
**********************************************************************************/  
float MQResistanceCalculation(int raw_adc)
{
  return ( ((float)RL_VALUE*(1023-raw_adc)/raw_adc));
}
  
/*************************** MQCalibration **************************************
Input:   mq_pin - analog channel
Output:  Ro of the sensor
Remarks: This function  assumes that the sensor is in clean air. It use  
         MQResistanceCalculation  to calculates the sensor resistance in clean air 
         and then divides it  with RO_CLEAN_AIR_FACTOR. RO_CLEAN_AIR_FACTOR is about 
         10, which differs  slightly between different sensors.
**********************************************************************************/  
float MQCalibration(int mq_pin)
{
  int i;
  float val=0;
 
  for (i=0;i<CALIBARAION_SAMPLE_TIMES;i++) {            //take multiple samples
    val += MQResistanceCalculation(analogRead(mq_pin));
    delay(CALIBRATION_SAMPLE_INTERVAL);
  }
  val = val/CALIBARAION_SAMPLE_TIMES;                   //calculate the average  value
 
  val = val/RO_CLEAN_AIR_FACTOR;                        //divided  by RO_CLEAN_AIR_FACTOR yields the Ro 
                                                        //according  to the chart in the datasheet 
 
  return val; 
}
/***************************  MQRead *******************************************
Input:   mq_pin - analog  channel
Output:  Rs of the sensor
Remarks: This function use MQResistanceCalculation  to caculate the sensor resistenc (Rs).
         The Rs changes as the sensor  is in the different consentration of the target
         gas. The sample times  and the time interval between samples could be configured
         by changing  the definition of the macros.
**********************************************************************************/  
float MQRead(int mq_pin)
{
  int i;
  float rs=0;
 
  for (i=0;i<READ_SAMPLE_TIMES;i++)  {
    rs += MQResistanceCalculation(analogRead(mq_pin));
    delay(READ_SAMPLE_INTERVAL);
  }
 
  rs = rs/READ_SAMPLE_TIMES;
 
  return rs;  
}
 
/***************************  MQGetGasPercentage ********************************
Input:   rs_ro_ratio -  Rs divided by Ro
         gas_id      - target gas type
Output:  ppm of the  target gas
Remarks: This function passes different curves to the MQGetPercentage  function which 
         calculates the ppm (parts per million) of the target  gas.
**********************************************************************************/  
int MQGetGasPercentage(float rs_ro_ratio, int gas_id)
{
  if ( gas_id  == GAS_LPG ) {
     return MQGetPercentage(rs_ro_ratio,LPGCurve);
  } else  if ( gas_id == GAS_CO ) {
     return MQGetPercentage(rs_ro_ratio,COCurve);
  } else if ( gas_id == GAS_SMOKE ) {
     return MQGetPercentage(rs_ro_ratio,SmokeCurve);
  }    
 
  return 0;
}
 
/***************************  MQGetPercentage  ********************************
Input:   rs_ro_ratio - Rs divided by Ro
         pcurve      - pointer to the curve of the target gas
Output:  ppm of  the target gas
Remarks: By using the slope and a point of the line. The x(logarithmic  value of ppm) 
         of the line could be derived if y(rs_ro_ratio) is provided.  As it is a 
         logarithmic coordinate, power of 10 is used to convert the  result to non-logarithmic 
         value.
**********************************************************************************/  
int  MQGetPercentage(float rs_ro_ratio, float *pcurve)
{
  return (pow(10,(  ((log(rs_ro_ratio)-pcurve[1])/pcurve[2]) + pcurve[0])));
}

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twig-gas_sensor_Ulm3DfPvdT.bmp

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