SHT31_SW

Arduino library for the SHT31 temperature and humidity sensor - using SoftWire.

Description

This experimental library features the class SHT31_SW derived from - https://github.com/RobTillaart/SHT31. It has the same interface as the SHT31 class so please use that documentation as it will be the "leading class".

The main difference is that the SHT31_SW class uses the SoftWire library for communication instead of the TwoWire based Wire class. See SHT31 PR #35.

SoftWire is a software I2C bus library to be able to select other pins than the default (AVR) hardware I2C pins (SDA and SCL). An important reason to use this version is when you want more than two devices on one Arduino.

SoftWire vs SoftwareWire

The SoftWire library is portable, however it could not read (on AVR) the SHT85 sensor which is command compatible with the SHT3x. A fix has been made in 0.3.0 and works on AVR (UNO) with an SHT31. See #12. It still has to be verified with an SHT85. The solution was to add buffers for I2C.

A separate repo is created based upon the AVR specific SoftwareWire see links below.

The SoftwareWire library is an AVR specific and worked for the SHT85. See https://github.com/RobTillaart/SHT31_SW/issues/5

SHT3x SHT85 sensors

The SHT3x family of sensors should work up to 1 MHz I2C although not tested above 400 MHz.

This library should also work for SHT30/35/85 but these are not tested yet.

Test on UNO

0.2.0 Breaking change

Version 0.2.0 introduced a breaking change in constructor and begin(). Parameters have moved from begin() to the constructor.

Related

These libraries need to be installed to get SHT31_SW working:

• https://github.com/RobTillaart/SHT31
• https://github.com/stevemarple/AsyncDelay
• https://github.com/stevemarple/SoftWire

Related

• https://github.com/Testato/SoftwareWire // AVR only

Interface

#include "SHT31_SW.h"

Note: The interface is mostly inherited from SHT31 but presented here for completeness.

Base interface

• SHT31_SW() constructor.
• bool begin(uint8_t address, SoftWire *wire = &Wire) for platforms with multiple I2C buses.
• bool begin(SoftWire *wire = &Wire) same as above. With default SHT_DEFAULT_ADDRESS.
• bool read(bool fast = true) blocks 4 (fast) or 15 (slow) milliseconds + actual read + math. Does read both the temperature and humidity.
• bool isConnected() check sensor is reachable over I2C. Returns false if not connected.
• uint16_t readStatus() details see datasheet and Status fields below.
• uint32_t lastRead() in milliSeconds since start of program.
• bool reset(bool hard = false) resets the sensor, soft reset by default. Returns false if it fails.
• 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.
• 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 you're worried about the extra cycles, you should make sure to cache these values or only request them after you've performed a new reading.

Error interface

• 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.

Heater interface

WARNING: Do not use heater for long periods.

Use the heater for max 180 seconds, and let it cool down 180 seconds = 3 minutes. SHT31 version 0.3.3 and up guards the cool down time by preventing switching the heater on within 180 seconds of the last switch off. Note: this guarding is not reboot persistent.

WARNING: The user is responsible to switch the heater off manually!

The class does NOT do this automatically. Switch off the heater by directly calling heatOff() or indirectly by calling isHeaterOn().

• void setHeatTimeout(uint8_t seconds) Set the time out of the heat cycle. This value is truncated to max 180 seconds.
• **uint8_t getHeatTimeout
• bool heatOn() switches heat cycle on if not already on. Returns false if fails, setting error to SHT31_ERR_HEATER_COOLDOWN or to SHT31_ERR_HEATER_ON.
• bool heatOff() switches heat cycle off. Returns false if fails, setting error to SHT31_ERR_HEATER_OFF.
• bool isHeaterOn() is the sensor still in heating cycle? replaces heatUp(). Will switch the heater off if max heating time has passed.
• bool heatUp() will be obsolete in the future. replaced by isHeaterOn()

Async interface

See async example for usage

• bool requestData() requests a new measurement. Returns false if this fails.
• bool dataReady() checks if enough time has passed to read the data. (15 milliseconds)
• bool readData(bool fast = true) fast = true skips the CRC check. Returns false if reading fails or in case of a CRC failure.

Status fields

Future

Must

• keep in sync with (leading) SHT31 and SHT31_SWW library.

Should

• remove script for atomic if not needed any more.
• verify SHT85 (as SHT31 works now).
• make isCOnnected() more robust, it now only fails on missing CLOCK.

Could

Wont

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Thank you,