_P014_SI7021.ino

//#######################################################################################################
//######################## Plugin 014 SI7021 I2C Temperature Humidity Sensor  ###########################
//#######################################################################################################
// 12-10-2015 Charles-Henri Hallard, see my projects and blog at https://hallard.me

#define PLUGIN_014
#define PLUGIN_ID_014        14
#define PLUGIN_NAME_014       "Temperature & Humidity - SI7021"
#define PLUGIN_VALUENAME1_014 "Temperature"
#define PLUGIN_VALUENAME2_014 "Humidity"

boolean Plugin_014_init = false;

// ======================================
// SI7021 sensor 
// ======================================
#define SI7021_I2C_ADDRESS    0x40 // I2C address for the sensor
#define SI7021_MEASURE_TEMP0  0xE0 // Can be read only after a RH conversion done
#define SI7021_MEASURE_TEMP   0xE3 // Default hold
#define SI7021_MEASURE_HUM    0xE5 // Default hold
#define SI7021_MEASURE_NOHOLD 0x80 // NO HOLD Bit flag
#define SI7021_WRITE_REG      0xE6
#define SI7021_READ_REG       0xE7
#define SI7021_SOFT_RESET     0xFE

// SI7021 Sensor resolution
// default at power up is SI7021_RESOLUTION_14T_12RH
#define SI7021_RESOLUTION_14T_12RH 0x00 // 12 bits RH / 14 bits Temp
#define SI7021_RESOLUTION_13T_10RH 0x80 // 10 bits RH / 13 bits Temp
#define SI7021_RESOLUTION_12T_08RH 0x01 //  8 bits RH / 12 bits Temp
#define SI7021_RESOLUTION_11T_11RH 0x81 // 11 bits RH / 11 bits Temp
#define SI7021_RESOLUTION_MASK 0B01111110

uint8_t  si7021_humidity;    // latest humidity value read
int16_t  si7021_temperature; // latest temperature value read (*100)

boolean Plugin_014(byte function, struct EventStruct *event, String& string)
{
  boolean success = false;

  switch (function)
  {
    case PLUGIN_DEVICE_ADD:
      {
        Device[++deviceCount].Number = PLUGIN_ID_014;
        Device[deviceCount].Type = DEVICE_TYPE_I2C;
        Device[deviceCount].VType = SENSOR_TYPE_TEMP_HUM;
        Device[deviceCount].Ports = 0;
        Device[deviceCount].PullUpOption = false;
        Device[deviceCount].InverseLogicOption = false;
        Device[deviceCount].FormulaOption = true;
        Device[deviceCount].ValueCount = 2;
        Device[deviceCount].SendDataOption = true;
        break;
      }

    case PLUGIN_GET_DEVICENAME:
      {
        string = F(PLUGIN_NAME_014);
        break;
      }

    case PLUGIN_GET_DEVICEVALUENAMES:
      {
        strcpy_P(ExtraTaskSettings.TaskDeviceValueNames[0], PSTR(PLUGIN_VALUENAME1_014));
        strcpy_P(ExtraTaskSettings.TaskDeviceValueNames[1], PSTR(PLUGIN_VALUENAME2_014));
        break;
      }

    case PLUGIN_WEBFORM_LOAD:
      {
        #define SI7021_RESOLUTION_OPTION 4

        byte choice = Settings.TaskDevicePluginConfig[event->TaskIndex][0];
        String options[SI7021_RESOLUTION_OPTION];
        int optionValues[SI7021_RESOLUTION_OPTION];
        optionValues[0] = SI7021_RESOLUTION_14T_12RH;
        options[0] = F("Temp 14 bits / RH 12 bits");
        optionValues[1] = SI7021_RESOLUTION_13T_10RH;
        options[1] = F("Temp 13 bits / RH 10 bits");
        optionValues[2] = SI7021_RESOLUTION_12T_08RH;
        options[2] = F("Temp 12 bits / RH  8 bits");
        optionValues[3] = SI7021_RESOLUTION_11T_11RH;
        options[3] = F("Temp 11 bits / RH 11 bits");

        string += F("<TR><TD>Resolution (bits):<TD><select name='plugin_014_res'>");
        for (byte x = 0; x < SI7021_RESOLUTION_OPTION; x++)
        {
          string += F("<option value='");
          string += optionValues[x];
          string += "'";
          if (choice == optionValues[x])
            string += F(" selected");
          string += ">";
          string += options[x];
          string += F("</option>");
        }
        string += F("</select>");

        success = true;
        break;
      }

    case PLUGIN_WEBFORM_SAVE:
      {
        String plugin1 = WebServer.arg("plugin_014_res");
        Settings.TaskDevicePluginConfig[event->TaskIndex][0] = plugin1.toInt();
        Plugin_014_init = false; // Force device setup next time
        success = true;
        break;
      }

    case PLUGIN_READ:
      {
        // Get sensor resolution configuration
        uint8_t res = Settings.TaskDevicePluginConfig[event->TaskIndex][0];

        if (!Plugin_014_init) {
          Plugin_014_init = Plugin_014_si7021_begin(res);
        }

        // Read values only if init has been done okay
        if (Plugin_014_init && Plugin_014_si7021_readValues(res) == 0) {
          UserVar[event->BaseVarIndex] = si7021_temperature/100.0;
          UserVar[event->BaseVarIndex + 1] = si7021_humidity;
          success = true;
          /*
          String log = F("SI7021 : Temperature: ");
          log += UserVar[event->BaseVarIndex];
          addLog(LOG_LEVEL_INFO,log);
          log = F("SI7021 : Humidity: ");
          log += UserVar[event->BaseVarIndex + 1];
          addLog(LOG_LEVEL_INFO,log);
          */
        } else {
          String log = F("SI7021 : Read Error!");
          addLog(LOG_LEVEL_INFO,log);
        }

        break;
      }

  }
  return success;
}

/* ======================================================================
Function: Plugin_014_si7021_begin
Purpose : read the user register from the sensor
Input   : user register value filled by function
Output  : true if okay
Comments: -
====================================================================== */
boolean Plugin_014_si7021_begin(uint8_t resolution)
{
  uint8_t ret;

  // Set the resolution we want
  ret = Plugin_014_si7021_setResolution(resolution);
  if ( ret == 0 ) {
    ret = true;
  } else {
    String log = F("SI7021 : Res=0x");
    log += String(resolution,HEX);
    log += F(" => Error 0x");
    log += String(ret,HEX);
    addLog(LOG_LEVEL_INFO,log);
    ret = false;
  }

  return ret; 
}

/* ======================================================================
Function: Plugin_014_si7021_checkCRC
Purpose : check the CRC of received data
Input   : value read from sensor
Output  : CRC read from sensor
Comments: 0 if okay
====================================================================== */
uint8_t Plugin_014_si7021_checkCRC(uint16_t data, uint8_t check)
{
  uint32_t remainder, divisor;

  //Pad with 8 bits because we have to add in the check value
  remainder = (uint32_t)data << 8; 

  // From: http://www.nongnu.org/avr-libc/user-manual/group__util__crc.html
  // POLYNOMIAL = 0x0131 = x^8 + x^5 + x^4 + 1 : http://en.wikipedia.org/wiki/Computation_of_cyclic_redundancy_checks
  // 0x988000 is the 0x0131 polynomial shifted to farthest left of three bytes
  divisor = (uint32_t) 0x988000;

  // Add the check value
  remainder |= check; 

  // Operate on only 16 positions of max 24. 
  // The remaining 8 are our remainder and should be zero when we're done.
  for (uint8_t i = 0 ; i < 16 ; i++) {
    //Check if there is a one in the left position
    if( remainder & (uint32_t)1<<(23 - i) ) 
      remainder ^= divisor;

    //Rotate the divisor max 16 times so that we have 8 bits left of a remainder
    divisor >>= 1; 
  }
  return ((uint8_t) remainder);
}

/* ======================================================================
Function: si7021_readRegister
Purpose : read the user register from the sensor
Input   : user register value filled by function
Output  : 0 if okay
Comments: -
====================================================================== */
int8_t Plugin_014_si7021_readRegister(uint8_t * value)
{
  uint8_t error ;

  // Request user register
  Wire.beginTransmission(SI7021_I2C_ADDRESS);
  Wire.write(SI7021_READ_REG); 
  Wire.endTransmission();
  
  // request 1 byte result  
  Wire.requestFrom(SI7021_I2C_ADDRESS, 1);
  if (Wire.available()>=1) {
      *value = Wire.read();
      return 0;
  }
  
  return 1;  
}

/* ======================================================================
Function: Plugin_014_si7021_startConv
Purpose : return temperature or humidity measured 
Input   : data type SI7021_READ_HUM or SI7021_READ_TEMP
          current config resolution
Output  : 0 if okay
Comments: internal values of temp and rh are set
====================================================================== */
int8_t Plugin_014_si7021_startConv(uint8_t datatype, uint8_t resolution)
{
  long data;
  uint16_t raw ;
  uint8_t checksum,tmp;
  uint8_t error;

  //Request a reading 
  Wire.beginTransmission(SI7021_I2C_ADDRESS);
  Wire.write(datatype);
  Wire.endTransmission();

  // Tried clock streching and looping until no NACK from SI7021 to know
  // when conversion's done. None have worked so far !!!
  // I fade up, I'm waiting maximum conversion time + 1ms, this works !!
  if (resolution == SI7021_RESOLUTION_11T_11RH)
    delay(4);
  else if (resolution == SI7021_RESOLUTION_12T_08RH)
    delay(5);
  else if (resolution == SI7021_RESOLUTION_13T_10RH)
    delay(8);
  else 
    delay(12);

  /*
  // Wait for data to become available, device will NACK during conversion
  tmp = 0;
  do 
  {
    // Request device
    Wire.beginTransmission(SI7021_I2C_ADDRESS);
    //Wire.write(SI7021_READ_REG); 
    error = Wire.endTransmission(true);
    delay(1);
  } 
  // always use time out in loop to avoid potential lockup (here 12ms max)
  // https://www.silabs.com/Support%20Documents/TechnicalDocs/Si7021-A20.pdf page 5
  while(error!=0 && tmp++<=12 );
  */
  Wire.requestFrom(SI7021_I2C_ADDRESS, 3);
  while ( Wire.available()<3 ) {
  }

  // Comes back in three bytes, data(MSB) / data(LSB) / Checksum
  raw  = ((uint16_t) Wire.read()) << 8;
  raw |= Wire.read();
  checksum = Wire.read();

  // Check CRC of data received
  if(Plugin_014_si7021_checkCRC(raw, checksum) != 0) {
    String log = F("SI7021 : checksum error!");
    addLog(LOG_LEVEL_INFO,log);
    return -1; 
  }

  // Humidity 
  if (datatype == SI7021_MEASURE_HUM) {
    // Convert value to Himidity percent 
    data = ((125 * (long)raw) >> 16) - 6;

    // Datasheet says doing this check
    if (data>100) data = 100;
    if (data<0)   data = 0;

    // save value
    si7021_humidity = (uint8_t) data;

  // Temperature
  } else {
    // Convert value to Temperature (*100)
    // for 23.45C value will be 2345
    data =  ((17572 * (long)raw) >> 16) - 4685;

    // save value
    si7021_temperature = (int16_t) data;
  }

  return 0;
}


/* ======================================================================
Function: Plugin_014_si7021_readValues
Purpose : read temperature and humidity from SI7021 sensor
Input   : current config resolution
Output  : 0 if okay
Comments: -
====================================================================== */
int8_t Plugin_014_si7021_readValues(uint8_t resolution)
{
  int8_t error = 0;

  // start humidity conversion
  error |= Plugin_014_si7021_startConv(SI7021_MEASURE_HUM, resolution);

  // start temperature conversion
  error |= Plugin_014_si7021_startConv(SI7021_MEASURE_TEMP, resolution);

  return error;
}

/* ======================================================================
Function: Plugin_014_si7021_setResolution
Purpose : Sets the sensor resolution to one of four levels 
Input   : see #define default is SI7021_RESOLUTION_14T_12RH
Output  : 0 if okay
Comments: -
====================================================================== */
int8_t Plugin_014_si7021_setResolution(uint8_t res)
{
  uint8_t reg;
  uint8_t error;

  // Get the current register value
  error = Plugin_014_si7021_readRegister(&reg);
  if ( error == 0) {
    // remove resolution bits
    reg &= SI7021_RESOLUTION_MASK ; 

    // Prepare to write to the register value
    Wire.beginTransmission(SI7021_I2C_ADDRESS);
    Wire.write(SI7021_WRITE_REG); 

    // Write the new resolution bits but clear unused before
    Wire.write(reg | ( res &= ~SI7021_RESOLUTION_MASK) ); 
    return (int8_t) Wire.endTransmission();
  } 

  return error;
}