GasAlarm.ino

/*Smoke Sensor  MQ7 mit LCD Display

  connect the MQ2 sensor as follows :

  VCC   >>> 5V

  AD0      >>> A0

  GND       >>> GND

  Contribution: epierre

  Based on http://sandboxelectronics.com/?p=165

  License: Attribution-NonCommercial-ShareAlike 3.0 Unported (CC BY-NC-SA 3.0)

*/

#include <LiquidCrystal.h>             //Sample using LiquidCrystal library

LiquidCrystal lcd(12, 11, 10, 7, 6, 5, 4);   // select the pins used on the LCD panel

#define   CHILD_ID_MQ                   0

/************************Hardware Related Macros************************************/

#define   MQ_SENSOR_ANALOG_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***********************************************/

unsigned long SLEEP_TIME = 30000; // Sleep time between reads (in milliseconds)

//VARIABLES

float Ro = 10000.0;    // this has to be tuned 10K Ohm

int val = 0;           // variable to store the value coming from the sensor

float valMQ = 0.0;

float lastMQ = 0.0;

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)

void setup()

{

  pinMode(2,OUTPUT);

  Serial.begin(9600);                               //UART setup, baudrate = 9600bps

  Serial.print("Calibrating...\n");

  lcd.begin(16, 2);                // start the LCD library

  lcd.setCursor(0, 0);             // set cursor position at start

  lcd.print("Kalibrierung ...");

  Serial.print("Setup ...");

  Ro = MQCalibration(MQ_SENSOR_ANALOG_PIN);

  // display standard

  lcd.clear();

  lcd.setCursor(0, 0);

  lcd.print("LPG:");

  lcd.setCursor(0, 1);

  lcd.print("SMOKE:");

  lcd.setCursor(12, 1);

  lcd.print("ppm");

}

void loop()

{

  Serial.print("LPG:");

  uint16_t valLPG = MQGetGasPercentage(MQRead(MQ_SENSOR_ANALOG_PIN) / Ro, GAS_LPG);

  Serial.println(valLPG);

  Serial.print("SMOKE:");

  uint16_t valSMOKE = MQGetGasPercentage(MQRead(MQ_SENSOR_ANALOG_PIN) / Ro, GAS_SMOKE);

  Serial.println(valSMOKE);

  if ((valLPG >= 10) || (valSMOKE >= 10)) {

    // Alarm wenn Grenzwert überschritten!

    Serial.println ("ALARM!");

     digitalWrite(2,HIGH);

     lcd.setCursor(0, 1); // clear digits

     lcd.print( "ALARM!!!" );

  }

  lcd.setCursor(4, 0); // clear digits

  lcd.print( "     " );

  lcd.setCursor(4, 0);

  lcd.print(valLPG);

  lcd.setCursor(6, 1); // clear digits

  lcd.print( "     " );

  lcd.setCursor(6, 1);

  lcd.print(valSMOKE);

}

/****************** 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])));

}