MQ2 Smoke/LPG Sensor

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Eric
Posts: 165
Joined: Fri Feb 21, 2014 4:52 pm

MQ2 Smoke/LPG Sensor

Post by Eric » Thu Feb 19, 2015 11:00 pm

Here is the information and code I used for getting my MQ2 smoke/LPG/Gas sensor up and running. You can find the original code I adapted here: http://sandboxelectronics.com/?p=165

Here is the code I made which outputs the values to a Nokia 5110 display as shown in my video. Take it enjoy and share it as you make it better:

Code: Select all

//E Found http://sandboxelectronics.com/?p=165
/*


This is a work in progress but hopefully it will help someone else by providing
a base to start and work from.
Please check out my Youtube videos here and consider a thumbs up if this helped you!
Youtube : http://www.youtube.com/user/Shadow5549
Website, Forum and store are at http://mkme.org

Pin 11 for contrast on the Nokia 5110
pin 7 - Serial clock out (SCLK)
pin 6 - Serial data out (DIN)
pin 5 - Data/Command select (D/C)
pin 4 - LCD chip select (CS)
pin 3 - LCD reset (RST)
*/


/*******************Demo for MQ-2 Gas Sensor Module V1.0*****************************
Support:  Tiequan Shao: support[at]sandboxelectronics.com
 
Lisence: Attribution-NonCommercial-ShareAlike 3.0 Unported (CC BY-NC-SA 3.0)
 
Note:    This piece of source code is supposed to be used as a demostration ONLY. More
         sophisticated calibration is required for industrial field application. 
 
                                                    Sandbox Electronics    2011-04-25
************************************************************************************/
 
/************************Hardware Related Macros************************************/
#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 
                                                     //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

#include "Adafruit_GFX.h"
#include "Adafruit_PCD8544.h"
Adafruit_PCD8544 display = Adafruit_PCD8544(7, 6, 5, 4, 3);//4 and 3 are reversed on the cheap eBay models

void setup()
{
  
  analogWrite(11,220);// PWM of LCD backlight but ebay unit is backwards- 
  //must go high + cycle to dim 
  //Very Dim=230
  Serial.println("Running..."); 
  display.begin();//Display code
  display.setContrast(60);//Nokia 5110 works best at 50- no more flicker
  delay(1000);
  display.clearDisplay();     // clears the screen and buffer
  display.setTextSize(1);     // set text size
  display.setTextColor(BLACK);
  //delay(1000);
  // Splash Personal- taken from example code
  display.setTextSize(1);
  display.setTextColor(BLACK);
  display.setCursor(0,0);
  display.println("   Eric's");
  display.println("");
  display.println("   Gizmos");
  display.println("   DooDad");
  display.println("    Thingy");
  display.display();
  delay(1000);
  display.clearDisplay();     // clears the screen and buffer
  Serial.begin(9600);  //UART setup, baudrate = 9600bps
  display.setCursor(0,0);
  display.println("Calibrating...");                
  display.display();
  Ro = MQCalibration(MQ_PIN);                       //Calibrating the sensor. Please make sure the sensor is in clean air 
                                                    //when you perform the calibration                    
  
  display.clearDisplay();
  display.println("Calibration is done..."); 
  display.print("Ro=");
  display.println(Ro);
  display.print("kohm");
  //display.println("\n");
  display.display();
  delay(3000);
   
}
 
void loop()
{
  display.clearDisplay();              // clears the screen and buffer
  display.setCursor(0,0);
  //display.print(" Intensity = ");
   display.print("LPG:"); 
   display.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_LPG) );
   display.println( "ppm" );
   //display.print("    ");   
   display.print("CO:"); 
   display.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_CO) );
   display.println( "ppm" );
   //display.print("    ");   
   display.print("SMOKE:"); 
   display.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_SMOKE) );
   display.print( "ppm" );
   //display.print("\n");
   display.display();
   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])));
}
Enjoy!

Eric
I make videos and content on all things electronics, 3D prining and "Maker"
http://www.mkme.org
https://www.youtube.com/mkmeorg

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