MQ2Lib/MQ2Lib.cpp at master · yanoschik/MQ2Lib · GitHub

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/* MQ2 gas sensor library
   Home: https://github.com/yanoschik/MQ2Lib
   (Based on: https://github.com/xerlay11/MQ-2-sensor-library)
*/
#include "MQ2Lib.h"

/* ----- constructor
   \param in   pin - sensor pin no.
   \param in   doSerial - true=do serial output [default=false]
*/
MQ2::MQ2(short pin, bool doSerial)
{
  _pin = pin;
  _serial = doSerial;
}

/* ----- Init */
void MQ2::begin()
{
  Ro = MQCalibration();
  if (_serial)
  {
    Serial.print(F("MQ2 Ro: "));
    Serial.print(Ro);
    Serial.println(F(" kohm"));
  }
}

/* ----- Read all
   \param in   print - true=print to serial (if enabled) [default=false]
*/
float* MQ2::read(bool print)
{
  MQRead();
  MQGetGasPercentage(read_val/Ro, MQ2_LPG);
  MQGetGasPercentage(read_val/Ro, MQ2_CO);
  MQGetGasPercentage(read_val/Ro, MQ2_SMOKE);

  if (print && _serial) //printing to serial (a bit complicated construction, but saving space for string constants)
  {
    for(int i=0; i<3; i++)
    {
      if(i==0)
      {
        Serial.print(F("LPG: "));
        Serial.print(values[MQ2_LPG]);
      }
      else
        Serial.print(F("  "));

      if(i==1)
      {
        Serial.print(F("CO: "));
        Serial.print(values[MQ2_CO]);
      }
      if(i==2)
      {
        Serial.print(F("SMOKE: "));
        Serial.print(values[MQ2_SMOKE]);
      }
      Serial.print(F("ppm"));
    }
    Serial.print(F("\n"));
  }

  return values;
}

/* ----- Read LPG */
float MQ2::readLPG()
{
  return MQGetGasPercentage(MQRead()/Ro, MQ2_LPG);
}

/* ----- Read CO */
float MQ2::readCO()
{
  return MQGetGasPercentage(MQRead()/Ro, MQ2_CO);
}

/* ----- Read smoke */
float MQ2::readSmoke()
{
  return MQGetGasPercentage(MQRead()/Ro, MQ2_SMOKE);
}

/* ----- Resistance calculation
   \param in   raw_adc - sensor value
*/
float MQ2::MQResistanceCalculation(int raw_adc)
{
  return (((float)MQ2_RL_VALUE*(1023-raw_adc)/raw_adc));
}

/* ----- Calibration */
float MQ2::MQCalibration()
{
  read_val = 0;
  for (int i=0; i<MQ2_CALIBARAION_SAMPLE_TIMES; i++) //take multiple samples
  {
    read_val += MQResistanceCalculation(analogRead(_pin));
    delay(MQ2_CALIBRATION_SAMPLE_INTERVAL);
  }

  read_val = read_val/MQ2_CALIBARAION_SAMPLE_TIMES;    //calculate the average value
  read_val = read_val/MQ2_RO_CLEAN_AIR_FACTOR;         //divided by RO_CLEAN_AIR_FACTOR yields the Ro
                                                       //according to the chart in the datasheet
  return read_val;
}

/* ----- Reading */
float MQ2::MQRead()
{
  if (millis() < (lastReadTime[0] + MQ2_READ_RATE))
    return read_val;

  read_val = 0;
  for (int i=0; i<MQ2_READ_SAMPLE_TIMES; i++)
  {
    read_val += MQResistanceCalculation(analogRead(_pin));
    delay(MQ2_READ_SAMPLE_INTERVAL);
  }

  read_val = read_val/MQ2_READ_SAMPLE_TIMES;    //calculate the average value
  lastReadTime[0] = millis();
  return read_val;
}

/* ----- Calculate specific gas percentage
   \param in   rs_ro_rato - read resistance ratio
   \param in   gas_id - id of gas, see defines
*/
float MQ2::MQGetGasPercentage(float rs_ro_ratio, short gas_id)
{
  if (gas_id != MQ2_LPG && gas_id != MQ2_CO && gas_id != MQ2_SMOKE)
    return 0;

  if (millis() < (lastReadTime[1+gas_id] + MQ2_READ_RATE))
    return values[gas_id];

  if (gas_id == MQ2_LPG)
    values[MQ2_LPG] = MQGetPercentage(rs_ro_ratio, LPGCurve);
  else if (gas_id == MQ2_CO)
    values[MQ2_CO] = MQGetPercentage(rs_ro_ratio, COCurve);
  else if (gas_id == MQ2_SMOKE)
    values[MQ2_SMOKE] = MQGetPercentage(rs_ro_ratio, SmokeCurve);
  else
    return 0; //redundant

  lastReadTime[1+gas_id] = millis();
  return values[gas_id];
}

/* ----- Calculate gas percentage
   \param in   rs_ro_rato - read resistance ratio
   \param in   pcurve - gas curve, see header
*/
float MQ2::MQGetPercentage(float rs_ro_ratio, const float *pcurve)
{
  return (pow(10,(((log(rs_ro_ratio)-pcurve[1])/pcurve[2]) + pcurve[0])));
}