HTU21D Class Reference

API for the HTU21D Temperature & Humidity Sensor. More...

Detailed Description

• ID: htu21d
• Name: Digital Relative Humidity Sensor with Temperature
• Category: temp
• Manufacturer: seeed adafruit sparkfun
• Link: http://www.meas-spec.com/downloads/HTU21D.pdf
• Connection: i2c

HTU21D by Measurement Specialties is a digital humidity sensor with temperature output. RH reports between 0 and 100%, and the temperature range is -40 to +125 degC. Note: getCompRH is the preferred function below (passing true to cause a measurement cycle). If actual values used for the compensated ready are necessary, use the getHumidity(false) and getTemperature(false) functions following the getCompRH call. Also note the sensor should not perform more than a couple of measurements per second to limit the heating of the sensor.

    float humidity = 0.0;
    float temperature = 0.0;
    float compRH = 0.0;

    upm::HTU21D sensor(0, HTU21D_I2C_ADDRESS);

    sensor.testSensor();

    while (!doWork) {
        compRH = sensor.getCompRH(true);
        humidity = sensor.getHumidity(false);
        temperature = sensor.getTemperature(false);

        std::cout << "humidity value = " << humidity << ", temperature value = " << temperature
                  << ", compensated RH value = " << compRH << std::endl;
        upm_delay_us(500000);
    }

Public Member Functions
	HTU21D (int bus, int devAddr=HTU21D_I2C_ADDRESS)
int	sampleData (void)
float	getHumidity (int bSampleData=false)
float	getTemperature (int bSampleData=false)
float	getCompRH (int bSampleData=false)
float	getDewPoint (int bSampleData=false)
int	getHumidityData (float *fHum, float *fHumTemp, float *fDewPt)
int	setHeater (int bEnable=false)
void	resetSensor (void)
int	testSensor (void)
mraa::Result	i2cWriteReg (uint8_t reg, uint8_t value)
uint16_t	i2cReadReg_16 (int reg)
uint8_t	i2cReadReg_8 (int reg)

Constructor & Destructor Documentation

HTU21D	(	int	bus,
		int	devAddr = HTU21D_I2C_ADDRESS
	)

Instantiates an HTU21D object

Parameters

bus	Number of the used bus
devAddr	Address of the used I2C device

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Member Function Documentation

int sampleData

(

void

)

Initiates a temperature/pressure mesasurement and waits to complete. The humidity and temperature registers can be read after this call.

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float getHumidity

(

int

bSampleData = false

)

Gets the current measured humidity [RH]

Parameters

bSampleData

Flag to sample sensor (default false)

Returns

Relative humidity in RH

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float getTemperature

(

int

bSampleData = false

)

Gets the humidity cell temperature [degC]

Parameters

bSampleData

Flag to sample sensor (default false)

Returns

Temperature in degC

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float getCompRH

(

int

bSampleData = false

)

Using the current humidity and temperature, the function calculates the compensated RH using the equation from the datasheet.

Parameters

bSampleData

Flag to sample sensor (default false)

Returns

Compensated relative humidity in RH

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float getDewPoint

(

int

bSampleData = false

)

Using the current humidity and temperature the function will calculate the dew point in degreeC based on equation from the datasheet.

Parameters

bSampleData

Flag to sample sensor (default false)

Returns

Dew point in degC

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int getHumidityData	(	float *	fHum,
		float *	fHumTemp,
		float *	fDewPt
	)

Function will attempt to get the best measurement for humidity using the heater in cases where humidity is high to keep the sesnsor dry. The heater setting is returned

Parameters

fHum	pointer to float for relative humidity RH
fHumTemp	pointer to float for temperature degC
fDewPt	pointer to float for calculated dew point degC

Returns

0 if success or 1 if sensor is not functioning

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int setHeater

(

int

bEnable = false

)

Sets the heater state. The heater is used to test the sensor functionality since the temperature should increase 0.5 to 1.5 degC, and the humidity should decrease. The testSensor() function below uses the heater.

Parameters

bEnable

Sets to non-zero to turn the heater on

Returns

0 on success

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void resetSensor

(

void

)

Performs a soft reset of the MPL3115A2 device to ensure it is in a known state. This function can be used to reset the min/max temperature and pressure values.

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int testSensor

(

void

)

Tests the device and verifies it is operating correctly.

Returns

0 on success or error code

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mraa::Result i2cWriteReg	(	uint8_t	reg,
		uint8_t	value
	)

Writes to a one-byte register

Parameters

reg	Address of the register
value	Byte to be written

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uint16_t i2cReadReg_16

(

int

reg

)

Reads a two-byte register. Note: byte ordering is hardware specific.

Parameters

reg	Address of the register

Returns

Value returned from register

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uint8_t i2cReadReg_8

(

int

reg

)

Reads a one-byte register

Parameters

reg	Address of the register

Returns

Value returned from register

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The documentation for this class was generated from the following files:

• src/htu21d/htu21d.hpp
• src/htu21d/htu21d.cpp