/**
* Reads current temperature-corrected relative humidity
*/
float SHT1x::readHumidity()
{
int _val; // Raw humidity value returned from sensor
float _linearHumidity; // Humidity with linear correction applied
float _correctedHumidity; // Temperature-corrected humidity
float _temperature; // Raw temperature value
// Conversion coefficients from SHT15 datasheet
const float C1 = -4.0; // for 12 Bit
const float C2 = 0.0405; // for 12 Bit
const float C3 = -0.0000028; // for 12 Bit
const float T1 = 0.01; // for 14 Bit @ 5V
const float T2 = 0.00008; // for 14 Bit @ 5V
// Command to send to the SHT1x to request humidity
int _gHumidCmd = 0b00000101;
// Fetch the value from the sensor
sendCommandSHT(_gHumidCmd, _dataPin, _clockPin);
waitForResultSHT(_dataPin);
_val = getData16SHT(_dataPin, _clockPin);
skipCrcSHT(_dataPin, _clockPin);
// Apply linear conversion to raw value
_linearHumidity = C1 + C2 * _val + C3 * _val * _val;
// Get current temperature for humidity correction
_temperature = readTemperatureC();
// Correct humidity value for current temperature
_correctedHumidity = _temperature * (T1 + T2 * _val) + _linearHumidity;
return (_correctedHumidity);
}
/**
* Reads current temperature-corrected relative humidity
*/
float sensirion::readHumidity()
{
uint16_t _val; // Raw humidity value returned from sensor
float _linearHumidity; // Humidity with linear correction applied
float _correctedHumidity; // Temperature-corrected humidity
float _temperature; // Raw temperature value
// Conversion coefficients from SHT15 datasheet
const float C1 = -4.0; // for 12 Bit
const float C2 = 0.0405; // for 12 Bit
const float C3 = -0.0000028; // for 12 Bit
const float T1 = 0.01; // for 14 Bit @ 5V
const float T2 = 0.00008; // for 14 Bit @ 5V
// Command to send to the SHT1x to request humidity
const uint8_t _gHumidCmd = 0b00000101;
// check cache
if ( millis() - _lastHumMillis < SHT_CACHE_MILLIS){
return _lastHumVal;
} else{
// Fetch the value from the sensor
if ( sendCommandSHT(_gHumidCmd, _dataPin, _clockPin) == SHT_SUCCESS ){
waitForResultSHT(_dataPin);
_val = getData16SHT(_dataPin, _clockPin);
uint8_t rxcrc = rev8bits( readCRC(_dataPin, _clockPin ) );
uint8_t mycrc = crc8add( 0, _gHumidCmd );
mycrc = crc8add( mycrc, _val );
if (mycrc != rxcrc){
Serial.println("SHT: crc error");
Serial.print(" Got: 0x"); Serial.println(rxcrc, HEX);
Serial.print(" Expected: 0x"); Serial.println(mycrc, HEX);
return NAN;
}
// Apply linear conversion to raw value
_linearHumidity = C1 + C2 * _val + C3 * _val * _val;
// Get current temperature for humidity correction
_temperature = readTemperatureC();
// Correct humidity value for current temperature
_correctedHumidity = (_temperature - 25.0 ) * (T1 + T2 * _val) + _linearHumidity;
// cache
_lastHumVal = _correctedHumidity;
_lastHumMillis = millis();
return (_correctedHumidity);
}
}
//error
return NAN;
}
