File content as of revision 0:a5033edf6975:

#include "MQ2.h"

void MQ2::begin(){
    Ro = MQCalibration();
}

/*
 * Reads data from MQ2.
 *
 * Param data: the pointer to fill.
 */
void MQ2::read(MQ2_data_t *data){
   data->lpg = MQGetGasPercentage(MQRead()/Ro,GAS_LPG);
   data->co = MQGetGasPercentage(MQRead()/Ro,GAS_CO);
   data->smoke = MQGetGasPercentage(MQRead()/Ro,GAS_SMOKE);
}

/*
 * reads data, returns LPG value in ppm
 */
float MQ2::readLPG(){
    return MQGetGasPercentage(MQRead()/10,GAS_LPG);
}

/*
 * reads data, returns CO value in ppm
 */
float MQ2::readCO(){
    return MQGetGasPercentage(MQRead()/10,GAS_CO);
}

/*
 * reads data, returns Smoke value in ppm
 */
float MQ2::readSmoke(){
    return MQGetGasPercentage(MQRead()/10,GAS_SMOKE);
}

float MQ2::MQResistanceCalculation(int raw_adc) {
   return (((float)RL_VALUE*(1023-raw_adc)/raw_adc));
}

float MQ2::MQCalibration() {
  float val=0;
  for (int i=0;i<CALIBARAION_SAMPLE_TIMES;i++) {                                //take multiple samples
    val += MQResistanceCalculation(_pin.read_u16()>>6);
    wait_ms(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; 
}

/*
 * Sample the MQ2
 */
float MQ2::MQRead() {
  int i;
  float rs=0;
  int val = _pin.read_u16()>>6;
  for (i=0;i<READ_SAMPLE_TIMES;i++) {
    rs += MQResistanceCalculation(val);
    wait_ms(READ_SAMPLE_INTERVAL);
  }
  rs = rs/READ_SAMPLE_TIMES;
  return rs;  
}

float MQ2::MQGetGasPercentage(float rs_ro_ratio, GasType gas_id) {
    switch(gas_id) {
        case GAS_LPG: return MQGetPercentage(rs_ro_ratio,LPGCurve);
        case GAS_CO: return MQGetPercentage(rs_ro_ratio,COCurve);
        case GAS_SMOKE: return MQGetPercentage(rs_ro_ratio,SmokeCurve);
        default: return -1.0;
    } 
}

int MQ2::MQGetPercentage(float rs_ro_ratio, float *pcurve) {
  return (pow(10,(((log(rs_ro_ratio)-pcurve[1])/pcurve[2]) + pcurve[0])));
}