SGP30.cpp

//
//    FILE: SGP30.cpp
//  AUTHOR: Rob Tillaart
// VERSION: 0.3.1
//    DATE: 2021-06-24
// PURPOSE: Arduino library for SGP30 environment sensor.
//     URL: https://github.com/RobTillaart/SGP30
//          https://www.adafruit.com/product/3709


#include "SGP30.h"


/////////////////////////////////////////////////////
//
//  CONSTRUCTOR
//
SGP30::SGP30(TwoWire *wire)
{
  _wire     = wire;
  _address  = 0x58;  //  Fixed!

  _tvoc     = 0;
  _co2      = 0;
  _h2       = 0;
  _ethanol  = 0;

  _lastTime = 0;
  _lastRequest = 0;
  _error    = SGP30_OK;
}


bool SGP30::begin()
{
  if (! isConnected()) return false;
  _init();
  return true;
}


bool SGP30::isConnected()
{
  _wire->beginTransmission(_address);
  return ( _wire->endTransmission() == 0);
}


bool SGP30::getID()
{
  _command(0x3682);
  delay(1);
  if (_wire->requestFrom(_address, (uint8_t)9) != 9)
  {
    _error = SGP30_ERROR_I2C;
    return false;
  }
  for (uint8_t i = 0; i < 6; )
  {
    _id[i++] = _wire->read();
    _id[i++] = _wire->read();
    uint8_t crc = _wire->read();
    uint16_t val = _id[i-2] * 256 + _id[i-1];
    if (_CRC8(val) != crc)
    {
      _error = SGP30_ERROR_CRC;
      return false;
    }
  }
  _error = SGP30_OK;
  return true;

}


//  expect to return 0x0022
uint16_t SGP30::getFeatureSet()
{
  _command(0x202F);
  delay(10);
  uint16_t rv = 0;
  if (_wire->requestFrom(_address, (uint8_t)3) == 3)
  {
    rv = _wire->read() << 8;
    rv  += _wire->read();
    uint8_t crc = _wire->read();
    if (_CRC8(rv) != crc)
    {
      _error = SGP30_ERROR_CRC;
      return rv;
    }
    _error = SGP30_OK;
    return rv;
  }
  _error = SGP30_ERROR_I2C;
  return 0xFFFF;
}


//  WARNING: resets all devices on I2C bus.
void SGP30::GenericReset()
{
  _command(0x0006);
  _init();
};


bool SGP30::measureTest()
{
  uint16_t rv = 0;
  _command(0x2032);
  delay(220);             //  Page 11
  if (_wire->requestFrom(_address, (uint8_t)3) == 3)
  {
    rv = _wire->read() << 8;
    rv  += _wire->read();
    uint8_t crc = _wire->read();
    if (_CRC8(rv) != crc)
    {
      _error = SGP30_ERROR_CRC;
      return false;
    }
    _error = SGP30_OK;
    return rv == 0xD400;
  }
  _error = SGP30_ERROR_I2C;
  return false;
}


/////////////////////////////////////////////////////
//
//  MEASUREMENT
//

//  SYNCHRONUOUS MODUS
bool SGP30::measure(bool all)      //  this is the workhorse
{
  //  1 second between measurements. Page 9
  if (millis() - _lastTime < 1000) return false;
  _lastTime = millis();

  request();
  delay(12);  //  blocking!!
  read();

  if (not all) return true;

  requestRaw();
  delay(25);  //  blocking!!
  readRaw();
  return true;
}


//  A-SYNCHRONUOUS INTERFACE
void SGP30::request()
{
  _lastRequest = millis();
  _command(0x2008);
}


bool SGP30::read()
{
  if (_lastRequest == 0) return false;
  if (millis() - _lastRequest < 13) return false;  //  Page 11
  _lastRequest = 0;

  if (_wire->requestFrom(_address, (uint8_t)6) != 6)
  {
    _error = SGP30_ERROR_I2C;
    return false;
  }
  _co2  =  _wire->read() << 8;
  _co2  += _wire->read();
  uint8_t crc = _wire->read();
  if (_CRC8(_co2) != crc)
  {
    _error = SGP30_ERROR_CRC;
    return false;
  }
  _tvoc =  _wire->read() << 8;
  _tvoc += _wire->read();
  crc = _wire->read();
  if (_CRC8(_tvoc) != crc)
  {
    _error = SGP30_ERROR_CRC;
    return false;
  }
  _error = SGP30_OK;
  return true;
}


void SGP30::requestRaw()
{
  _lastRequest = millis();
  _command(0x2050);
}


bool SGP30::readRaw()
{
  if (_lastRequest == 0) return false;
  if (millis() - _lastRequest < 26) return false;  //  Page 11
  _lastRequest = 0;

  if (_wire->requestFrom(_address, (uint8_t)6) != 6)
  {
    _error = SGP30_ERROR_I2C;
    return false;
  }
  _h2      =  _wire->read() << 8;
  _h2      += _wire->read();
  uint8_t crc = _wire->read();
  if (_CRC8(_h2) != crc)
  {
    _error = SGP30_ERROR_CRC;
    return false;
  }
  _ethanol =  _wire->read() << 8;
  _ethanol += _wire->read();
  crc = _wire->read();
  if (_CRC8(_ethanol) != crc)
  {
    _error = SGP30_ERROR_CRC;
    return false;
  }
  _error = SGP30_OK;
  return true;
}


//  experimental - datasheet Page 2
//  1.953125e-3 = 1/512
float SGP30::getH2()
{
  float cref = 0.5;  //  ppm
  return cref * exp((_srefH2 - _h2) * 1.953125e-3);
}


float SGP30::getEthanol()
{
  float cref = 0.4;  //  ppm
  return cref * exp((_srefEth - _ethanol) * 1.953125e-3);
}


/////////////////////////////////////////////////////
//
//  CALIBRATION
//

//  T  in °C
//  RH == RelativeHumidity
float SGP30::setRelHumidity(float T, float RH)      //  Page 10
{
  //  page 10 datasheet
  //  AH = AbsoluteHumidity
  //  uint16_t AH = 216.7 * RH/100 * 6.117 * exp((17.62 * T)/(243.12 + T)) / (273.15 + T);
  float absoluteHumidity = (2.167 * 6.112) * RH ;
  absoluteHumidity *= exp((17.62 * T)/(243.12 + T));
  absoluteHumidity /=  (273.15 + T);

  setAbsHumidity(absoluteHumidity);
  return absoluteHumidity;
}


void SGP30::setAbsHumidity(float absoluteHumidity)
{
  uint16_t AH = absoluteHumidity;
  uint8_t tmp = (absoluteHumidity - AH) * 256;
  AH = (AH << 8) | tmp;

  _command(0x2061, AH);     //  Page 11
}


void SGP30::setBaseline(uint16_t CO2, uint16_t TVOC)
{
  _command(0x201E, TVOC, CO2);
}


bool SGP30::getBaseline(uint16_t *CO2, uint16_t *TVOC)
{
  _command(0x2015);
  if (_wire->requestFrom(_address, (uint8_t)6) != 6)
  {
    _error = SGP30_ERROR_I2C;
    return false;
  }
  *CO2  =  _wire->read() << 8;
  *CO2  += _wire->read();
  uint8_t crc = _wire->read();
  if (_CRC8(*CO2) != crc)
  {
    _error = SGP30_ERROR_CRC;
    return false;
  }
  *TVOC =  _wire->read() << 8;
  *TVOC += _wire->read();
  crc = _wire->read();
  if (_CRC8(*TVOC) != crc)
  {
    _error = SGP30_ERROR_CRC;
    return false;
  }
  _error = SGP30_OK;
  return true;
}


void SGP30::setTVOCBaseline(uint16_t TVOC)
{
  _command(0x2077, TVOC);
}


bool SGP30::getTVOCBaseline(uint16_t *TVOC)
{
  _command(0x20B3);
  if (_wire->requestFrom(_address, (uint8_t)3) != 3)
  {
    _error = SGP30_ERROR_I2C;
    return false;
  }
  *TVOC =  _wire->read() << 8;
  *TVOC += _wire->read();
  uint8_t crc = _wire->read();
  if (_CRC8(*TVOC) != crc)
  {
    _error = SGP30_ERROR_CRC;
    return false;
  }
  _error = SGP30_OK;
  return true;
}


/////////////////////////////////////////////////////
//
//  MISCELLANEOUS
//
int SGP30::lastError()
{
  int error = _error;
  _error = SGP30_OK;
  return error;
}


/////////////////////////////////////////////////////
//
//  PRIVATE
//
int SGP30::_command(uint16_t cmd)
{
  _wire->beginTransmission(_address);
  _wire->write(cmd >> 8);
  _wire->write(cmd & 0xFF);
  _error = _wire->endTransmission();
  return _error;
}


int SGP30::_command(uint16_t cmd, uint16_t v1)
{
  _wire->beginTransmission(_address);
  _wire->write(cmd >> 8);
  _wire->write(cmd & 0xFF);
  _wire->write(v1 >> 8);
  _wire->write(v1 & 0xFF);
  _wire->write(_CRC8(v1));
  _error = _wire->endTransmission();
  return _error;
}


int SGP30::_command(uint16_t cmd, uint16_t v1, uint16_t v2)
{
  _wire->beginTransmission(_address);
  _wire->write(cmd >> 8);
  _wire->write(cmd & 0xFF);
  _wire->write(v1 >> 8);
  _wire->write(v1 & 0xFF);
  _wire->write(_CRC8(v1));
  _wire->write(v2 >> 8);
  _wire->write(v2 & 0xFF);
  _wire->write(_CRC8(v2));
  _error = _wire->endTransmission();
  return _error;
}


//  for sending command - CRC lib.
//  always 2 bytes
uint8_t SGP30::_CRC8(uint16_t data)
{
  uint8_t val[2];
  val[0] = data >> 8;
  val[1] = data & 0xFF;

  uint8_t crc = 0xFF;             //  start value
  for(uint8_t i = 0; i < 2; i++)
  {
    crc ^= val[i];
    for (uint8_t b = 8; b > 0; b--)
    {
      if (crc & 0x80)
        crc = (crc << 1) ^ 0x31;  //  polynomial
      else
        crc <<= 1;
    }
  }
  return crc;
};


void SGP30::_init()
{
  _command(0x2003);
};


//  -- END OF FILE --