5.6 KiB
SHT31
Arduino library for the SHT31 temperature and humidity sensor
Relates to the SHT85 library - https://github.com/RobTillaart/SHT85
Description
The SHT3x family of sensors should work up to 1 MHz I2C
This library should also work for SHT30 and SHT35 but these are not tested yet.
| SENSOR | Temperature accuracy | Humidity accuracy |
|---|---|---|
| SHT30 | ~0.3 | 2.0 |
| SHT31 | ~0.3 | 1.5 |
| SHT35 | ~0.2 | 1.5 |
| SHT85 | ~0.2 | 1.5 |
An elaborated library for the SHT31 sensor can be found here https://github.com/hawesg/SHT31D_Particle_Photon_ClosedCube
Interface
Base interface
- SHT31() constructor.
- begin(address, dataPin, clockPin) begin function for ESP8266 & ESP32; returns false if device address is incorrect or device cannot be reset.
- begin(address) for single I2C bus platforms, e.g UNO.
- begin(address, TwoWire *wire) for platforms with multiple I2C busses.
- read(bool fast = true) blocks 4 (fast) or 15 (slow) milliseconds + actual read + math. Does read both the temperature and humidity.
- 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.
- reset(bool hard = false) resets the sensor, soft reset by default. Returns false if fails.
- getHumidity() computes the relative humidity in % based off the latest raw reading, and returns it
- getTemperature() computes the temperature in °C based off the latest raw reading, and returns it
- getRawHumidity() returns the raw two-byte representation of humidity directly from the sensor
- 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
- 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.
| Error | Symbolic | Description |
|---|---|---|
| 0x00 | SHT31_OK | no error |
| 0x81 | SHT31_ERR_WRITECMD | I2C write failed |
| 0x82 | SHT31_ERR_READBYTES | I2C read failed |
| 0x83 | SHT31_ERR_HEATER_OFF | Could not switch off heater |
| 0x84 | SHT31_ERR_NOT_CONNECT | Could not connect |
| 0x85 | SHT31_ERR_CRC_TEMP | CRC error in temperature |
| 0x86 | SHT31_ERR_CRC_HUM | CRC error in humidity |
| 0x87 | SHT31_ERR_CRC_STATUS | CRC error in statusfield |
Heater interface
Use the heater for max 180 seconds, and let it cool down an equal period of time.
WARNING: Do not use heater for long periods.
WARNING: The user is responsible to switch the heater off manually! The class does NOT do this automatically.
- setHeatTimeout(uint8_t seconds) Set the time out of the heat cycle. This value is truncated to max 180 seconds.
- heatOn() switches heat cycle on. Returns false if fails.
- heatOff() switches heat cycle off. Returns false if fails.
- isHeaterOn() is the sensor still in heating cycle? replaces heatUp(). Will switch heat off if max heating time has passed.
- heatUp() will be obsolete in the future.
Async interface
See async example for usage
- requestData() requests a new measurement. Returns false if this fails.
- dataReady() checks if enough time has passed to read the data. (15 millis)
- readData(bool fast = true) fast skips CRC check. Returns false if reading fails or in case of a CRC fail.
Status fields
| BIT | Description | values |
|---|---|---|
| 15 | Alert pending status | '0': no pending alerts |
| '1': at least one pending alert - default | ||
| 14 | Reserved | '0' |
| 13 | Heater status | '0’ : Heater OFF - default |
| '1’ : Heater ON | ||
| 12 | Reserved | '0' |
| 11 | Humidity tracking alert | '0’ : no alert - default |
| '1’ : alert | ||
| 10 | Temperature tracking alert | '0’ : no alert - default |
| '1’ : alert | ||
| 9-5 | Reserved | '00000' |
| 4 | System reset detected | '0': no reset since last ‘clear status register’ command |
| '1': reset detected (hard or soft reset command or supply fail) - default | ||
| 3-2 | Reserved | '00' |
| 1 | Command status | '0': last cmd executed successfully |
| '1': last cmd not processed. Invalid or failed checksum | ||
| 0 | Write data checksum status | '0': checksum of last write correct |
| '1': checksum of last write transfer failed |
Future
- merge with other SHT sensors if possible
- direct Fahrenheit formula
Operation
See examples