Arduino library for the I2C SHT4x temperature and humidity sensor.

The SHT4x family is the 4th generation of Sensirion Humidity and Temperature sensors.

This library is build upon the https://github.com/RobTillaart/SHT31 library. The reason for this (extra) SHT4x library is to have an asynchronous interface like the SHT31 library has.

The most important difference with the SHT31 seems to be the way the heater is implemented and can be used. More information on how to use properly the heater can be found in the SHT4x datasheet and in the Sensirion application note "Using the Integrated Heater of SHT4x in High-Humidity Environments".

This library has implemented an overheat protection by blocking heating calls until a defined interval has passed. The interval is mentioned in table below. This interval is based on a 10% duty cycle for 200 mW. Thus, the average power is limited to 20 mW.

Datasheet used: Version 7.1 – March 2025.

Accuracy table

The datasheet states 3 different accuracies for the SHT43.

For more details, please read the datasheet (check https://sensirion.com )

An elaborated library for the SHT4x sensor can be found here

• https://github.com/Sensirion/arduino-i2c-sht4x

As always feedback is welcome.

The SHT4x family of sensors should work up to 1 MHz I2C.

The library does not support "softWare I2C" based SHT4x.

The library and device work from 100 to 850 kHz - not tested beyond.

The I2C performance is mostly relevant when using the async interface as the synchronous read() call will block much longer.

The SHT4x sensors have a fixed I2C address, however they can be ordered with one of three addresses, 0x44, 0x45 or 0x46. Not all addresses seem to be available for all the different SHT4x sensors. Check latest datasheet for details.

Sometimes you need to control more devices than possible with the default address range the device provides. This is possible with an I2C multiplexer e.g. TCA9548 which creates up to eight channels (think of it as I2C subnets) which can use the complete address range of the device.

Drawback of using a multiplexer is that it takes more administration in your code e.g. which device is on which channel. This will slow down the access, which must be taken into account when deciding which devices are on which channel. Also note that switching between channels will slow down other devices too if they are behind the multiplexer.

• https://github.com/RobTillaart/TCA9548

SHT series temperature sensors

• https://github.com/RobTillaart/SHT2x
• https://github.com/RobTillaart/SHT31 Sensirion humidity / temperature sensor
• https://github.com/RobTillaart/SHT31_SW = softWire based I2C.
• https://github.com/RobTillaart/SHT31_SWW = softWire based I2C.
• https://github.com/RobTillaart/SHT85 Sensirion humidity / temperature sensor
• https://github.com/RobTillaart/tinySHT2x

Other temperature sensors

• https://github.com/RobTillaart/DHTNew DHT11/22 etc
• https://github.com/RobTillaart/DHTStable DHT11/22 etc
• https://github.com/RobTillaart/DHT_Simulator
• https://github.com/RobTillaart/DS18B20_INT OneWire temperature sensor
• https://github.com/RobTillaart/DS18B20_RT OneWire temperature sensor

An elaborated library for the SHT31 sensor can be found here

• https://github.com/hawesg/SHT31D_Particle_Photon_ClosedCube

Other, including Dew-point, heat-index, related functions and conversions.

• https://www.kandrsmith.org/RJS/Misc/Hygrometers/calib_many.html (interesting)
• https://github.com/RobTillaart/Temperature (conversions, dewPoint, heat index etc.)

#include "SHT4x.h"

• SHT4x(uint8_t address = SHT_DEFAULT_ADDRESS, TwoWire *wire = &Wire) constructor. Optional select address and the I2C bus (Wire, Wire1 etc.). The SHT_DEFAULT_ADDRESS = 0x44.
• bool begin() Returns false if device address is incorrect or device cannot be reset.
• bool isConnected() checks if device address can be seen on I2C bus. Returns false if not connected.
• uint8_t getAddress() returns device address set in the constructor.

• bool read(measType measurementType = SHT4x_MEASUREMENT_SLOW, bool CRCCheck = true)
  • SHT4x_MEASUREMENT_SLOW : High precision measurement
  • SHT4x_MEASUREMENT_MEDIUM : Medium precision measurement
  • SHT4x_MEASUREMENT_FAST : Low precision measurement
  • SHT4x_MEASUREMENT_LONG_HIGH_HEAT : activate heater with 200mW for 1s including a high precision measurement just before deactivation
  • SHT4x_MEASUREMENT_SHORT_HIGH_HEAT : activate heater with 200mW for 0.1s including a high precision measurement just before deactivation
  • SHT4x_MEASUREMENT_LONG_MEDIUM_HEAT :activate heater with 110mW for 1s including a medium precision measurement just before deactivation
  • SHT4x_MEASUREMENT_SHORT_MEDIUM_HEAT :activate heater with 110mW for 0.1s including a medium precision measurement just before deactivation
  • SHT4x_MEASUREMENT_LONG_LOW_HEAT :activate heater with 20mW for 1s including a low precision measurement just before deactivation
  • SHT4x_MEASUREMENT_SHORT_LOW_HEAT :activate heater with 20mW for 0.1s including a low precision measurement just before deactivation
  • CRCCheck: CRCCheck = true does the CRC check. Returns false if reading fails or in case of a CRC failure. Equivalent to fast = false in the SHT31 library.

Note that the call to read() blocks for a serious amount of time. If needed use the Async interface as this allows to do other tasks while waiting for the measurement. See Async interface section below.

Meta information about the sensor.

• uint32_t lastRead() timestamp of last successful read() in milliSeconds since start of program.
• bool reset(bool fast = false) resets the sensor, soft reset by default. Returns false if call fails. Note that reset() blocks for 1 ms so sensor can reinitialize unless parameter fast == true.

The following functions will return the same value until a new read() call (or async equivalent) is made.

• float getHumidity() computes the relative humidity in % based on the latest raw reading, and returns it.
• float getTemperature() computes the temperature in °C based on the latest raw reading, and returns it.
• float getFahrenheit() computes the temperature in °F based on the latest raw reading, and returns it.

The getRawHumidity() and getRawTemperature() can be used to minimize storage or communication as the data type is 50% smaller. Another application for the raw data, is faster comparison with a previous value or threshold, or to use integer only math (possibly at cost of some precision).

• uint16_t getRawHumidity() returns the raw two-byte representation of humidity directly from the sensor.
• uint16_t getRawTemperature() returns the raw two-byte representation of temperature directly from the sensor.

Note that the temperature and humidity values are recalculated on every call to getHumidity() and getTemperature(). If performance is an issue you should cache the values and only request them after a new reading.

• int getError() returns last set error flag and clear it. Be sure to clear the error flag by calling getError() before calling any command as the error flag could be from a previous command.

Some error codes are not used and are kept because inherited from "parent lib" SHT31.

See async example for usage

• bool requestData(measType measurementType = SHT4x_MEASUREMENT_SLOW) requests a new measurement. Returns false if this fails. See read() for the possible input.
• bool dataReady() checks if enough time has passed to read the data.
• bool readData(bool CRCCheck = true) CRCCheck = true does the CRC check. Returns false if reading fails or in case of a CRC failure. Equivalent to fast = false in the SHT31 library.

• bool heatingReady() Returns true if enough time has passed to call for another measurement with heat.
• void setHeatProtection(bool activateHeatProtection) If activateHeatProtection == true, which is the default value at initialisation, heating interval is validated before sending another heating command. If activateHeatProtection == false, this protection is deactivated.

• bool getSerialNumber(uint32_t &serial, bool CRCCheck = true) CRCCheck == true, => CRC check, slower CRCCheck == false, => no CRC check, faster.

• get documentation right
• test functionality with hardware

• check error handling
  • missing or not used codes.
  • set _error where needed.

• extend unit-tests if possible.

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