DFRobot_SFA40.cpp

/*!
 * @file DFRobot_SFA40.cpp
 * @brief  Implementation of DFRobot_SFA40 class methods
 * @copyright  Copyright (c) 2025 DFRobot Co.Ltd (http://www.dfrobot.com)
 * @license The MIT License (MIT)
 * @author [fary](feng.yang@dfrobot.com)
 * @version V1.0.4
 * @date 2026-06-29
 * @url https://github.com/DFRobot/DFRobot_SFA40
 */
#include "DFRobot_SFA40.h"

static const uint16_t SFA40_COMMAND_READ_B4 = 0xE06D;
static const uint16_t SFA40_COMMAND_ID_B4   = 0x0559;

void DFRobot_SFA40::detectProtocol(void){
  stopMeasurement();
  delay(30);

  memset(_buf, 0, sizeof(_buf));
  if(readReg(SFA40_COMMAND_ID, _buf, 9) == 9){
    bool valid = true;
    for(uint8_t i = 0; i < 9; i += 3){
      if(calcCrc(_buf + i, 2) != _buf[i + 2]){
        valid = false;
        break;
      }
    }
    if(valid){
      _readCommand = SFA40_COMMAND_READ;
      _serialCommand = SFA40_COMMAND_ID;
      _statusIndex = 9;
      _serialReadSize = 9;
      serialNumberLen = 6;
      return;
    }
  }

  memset(_buf, 0, sizeof(_buf));
  if(readReg(SFA40_COMMAND_ID_B4, _buf, 15) == 15){
    bool valid = true;
    for(uint8_t i = 0; i < 15; i += 3){
      if(calcCrc(_buf + i, 2) != _buf[i + 2]){
        valid = false;
        break;
      }
    }
    if(valid){
      _readCommand = SFA40_COMMAND_READ_B4;
      _serialCommand = SFA40_COMMAND_ID_B4;
      _statusIndex = 10;
      _serialReadSize = 15;
      serialNumberLen = 10;
      return;
    }
  }

  _readCommand = SFA40_COMMAND_READ;
  _serialCommand = SFA40_COMMAND_ID;
  _statusIndex = 9;
  _serialReadSize = 9;
  serialNumberLen = 6;
}

byte DFRobot_SFA40::begin(void){
  _pWire->begin();
  _pWire->beginTransmission(_deviceAddr);
  byte ret = _pWire->endTransmission();
  if(ret != 0){
    return ret;
  }
  detectProtocol();
  return 0;
}

void DFRobot_SFA40::startMeasurement(void){
  writeReg(SFA40_COMMAND_START);
}

void DFRobot_SFA40::stopMeasurement(void){
  writeReg(SFA40_COMMAND_STOP);
}

uint8_t DFRobot_SFA40::calcCrc(uint8_t data[], uint8_t length){
  uint8_t crc = SFA40_CRC_INITIAL_VALUE;
  for(uint8_t i = 0; i < length; i++){
    crc ^= data[i];
    for(uint8_t bit = 8; bit > 0; --bit){
      if(crc & 0x80){
        crc = ((crc << 1) ^ SFA40_CRC_POLYNOMIAL) & 0xFF;
      }else{
        crc = (crc << 1) & 0xFF;
      }
    }
  }
  return crc;
}

uint8_t *DFRobot_SFA40::getSerialNumber(void){
  memset(_buf, 0, sizeof(_buf));
  memset(serialNumber, 0, sizeof(serialNumber));
  if(readReg(_serialCommand, _buf, _serialReadSize) != (int)_serialReadSize){
    serialNumberLen = 0;
    return NULL;
  }
  for(uint8_t i = 0; i < _serialReadSize; i += 3){
    if(calcCrc(_buf + i, 2) != _buf[i + 2]){
      serialNumberLen = 0;
      return NULL;
    }
    serialNumber[i / 3 * 2] = _buf[i];
    serialNumber[i / 3 * 2 + 1] = _buf[i + 1];
  }
  return serialNumber;
}

uint8_t DFRobot_SFA40::readMeasurementData(void){
  memset(_buf, 0, 12);
  HCHO = NAN;
  humidity = NAN;
  temperatureC = NAN;
  temperatureF = NAN;
  if(readReg(_readCommand, _buf, 12) != 12){
    return 3;
  }
  for(uint8_t i = 0; i < 9; i += 3){
    if(calcCrc(_buf + i, 2) != _buf[i + 2]){
      return 3;
    }
  }
  if(calcCrc(_buf + 9, 2) != _buf[11]){
    return 3;
  }
  HCHO = (_buf[0] * 256 + _buf[1]) / 10.0;
  humidity = 125.0 * ((_buf[3] * 256 + _buf[4]) / 65535.0) - 6;
  if(humidity < 0){
    humidity = 0;
  }
  if(humidity > 100){
    humidity = 100;
  }
  temperatureC = 175.0 * ((_buf[6] * 256 + _buf[7]) / 65535.0) - 45;
  temperatureF = 315.0 * ((_buf[6] * 256 + _buf[7]) / 65535.0) - 49;
  if(_buf[_statusIndex] & 0x01){
    return 1;
  }
  if(_buf[_statusIndex] & 0x02){
    return 2;
  }
  return 0;
}

void DFRobot_SFA40::writeReg(uint16_t command){
  _pWire->beginTransmission(_deviceAddr);
  _pWire->write(command >> 8);
  _pWire->write(command & 0xFF);
  _pWire->endTransmission();
}

int DFRobot_SFA40::readReg(uint16_t command, void* pBuf, size_t size){
  if(pBuf == NULL){
    DBG("pBuf ERROR!! : null pointer");
    return -1;
  }
  uint8_t *_pBuf = (uint8_t *)pBuf;
  _pWire->beginTransmission(_deviceAddr);
  _pWire->write(command >> 8);
  _pWire->write(command & 0xFF);
  if(_pWire->endTransmission() != 0){
    DBG("endTransmission ERROR!!");
    return 0;
  }
  if(_pWire->requestFrom(_deviceAddr, (uint8_t)size) != size){
    DBG("requestFrom ERROR!!");
    return 0;
  }
  for(size_t i = 0; i < size; i++){
    _pBuf[i] = _pWire->read();
  }
  return (int)size;
}