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184 lines
8.1 KiB
Markdown
184 lines
8.1 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/SHT31_SW/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/SHT31_SW/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/SHT31_SW/blob/master/LICENSE)
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[](https://github.com/RobTillaart/SHT31_SW/releases)
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# SHT31_SW
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Arduino library for the SHT31 temperature and humidity sensor - using **SoftwareWire**.
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## Description
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This library features the class SHT31_SW derived from - https://github.com/RobTillaart/SHT31
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It has the same interface as the SHT31 class so please use that documentation
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as it will be the "leading class".
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The main difference is that this SHT31_SW class uses the **SoftwareWire**
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library for communication instead of the **TwoWire** based **Wire** class.
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**SoftwareWire** is a software I2C bus library to be able to select other pins
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than the default (AVR) hardware I2C pins (SDA and SCL).
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An important reason to use this version is when you want more than two
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devices on one Arduino.
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#### Status
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- experimental
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- created as alternative for SHT31 PR #35.
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- 0.1.0 uses SoftwareWire which also works for the SHT85. (see issue #5)
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- The footprint for SoftwareWire is ~500 bytes smaller (on UNO).
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#### SHT sensors
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The SHT3x family of sensors should work up to 1 MHz I2C (although
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This library should also work for SHT30/35/85 but these are not tested yet.
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Accuracy table
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| SENSOR | Temperature | Humidity |
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|:--------:|:-------------:|:----------:|
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| SHT30 | ~0.3 | 2.0 |
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| SHT31 | ~0.3 | 1.5 |
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| SHT35 | ~0.2 | 1.5 |
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| SHT85 | ~0.2 | 1.5 |
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#### Links
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These libraries need to be installed to get SHT31_SW working:
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- https://github.com/RobTillaart/SHT31
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- https://github.com/Testato/SoftwareWire
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## Interface
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```cpp
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#include "SHT31_SWW.h"
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```
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Note: The interface is mostly inherited from SHT31 but presented here for completeness.
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#### Base interface
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- **SHT31_SWW()** constructor.
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- **bool begin(uint8_t address, SoftwareWire \*wire = &Wire)** for platforms with multiple I2C buses.
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- **bool begin(SoftwareWire \*wire = &Wire)** same as above. With default SHT_DEFAULT_ADDRESS.
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- **bool read(bool fast = true)** blocks 4 (fast) or 15 (slow) milliseconds + actual read + math.
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Does read both the temperature and humidity.
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- **bool isConnected()** check sensor is reachable over I2C. Returns false if not connected.
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- **uint16_t readStatus()** details see datasheet and **Status fields** below.
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- **uint32_t lastRead()** in milliSeconds since start of program.
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- **bool reset(bool hard = false)** resets the sensor, soft reset by default. Returns false if it fails.
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- **float getHumidity()** computes the relative humidity in % based on the latest raw reading, and returns it.
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- **float getTemperature()** computes the temperature in <20>C based on the latest raw reading, and returns it.
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- **float getFahrenheit()** computes the temperature in <20>F based on the latest raw reading, and returns it.
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- **uint16_t getRawHumidity()** returns the raw two-byte representation of humidity directly from the sensor.
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- **uint16_t getRawTemperature()** returns the raw two-byte representation of temperature directly from the sensor.
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Note that the temperature and humidity values are recalculated on every call to **getHumidity()** and **getTemperature()**.
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If you're worried about the extra cycles, you should make sure to cache these values or only request them after
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you've performed a new reading.
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#### Error interface
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- **int getError()** returns last set error flag and clear it.
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Be sure to clear the error flag by calling **getError()** before calling any command as the error flag could be from a previous command.
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| Error | Symbolic | Description |
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|:-------:|:----------------------------|:------------------------------|
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| 0x00 | SHT31_OK | no error |
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| 0x81 | SHT31_ERR_WRITECMD | I2C write failed |
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| 0x82 | SHT31_ERR_READBYTES | I2C read failed |
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| 0x83 | SHT31_ERR_HEATER_OFF | Could not switch off heater |
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| 0x84 | SHT31_ERR_NOT_CONNECT | Could not connect |
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| 0x85 | SHT31_ERR_CRC_TEMP | CRC error in temperature |
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| 0x86 | SHT31_ERR_CRC_HUM | CRC error in humidity |
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| 0x87 | SHT31_ERR_CRC_STATUS | CRC error in status field |
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| 0x88 | SHT31_ERR_HEATER_COOLDOWN | Heater need to cool down |
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| 0x88 | SHT31_ERR_HEATER_ON | Could not switch on heater |
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#### Heater interface
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**WARNING:** Do not use heater for long periods.
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Use the heater for max **180** seconds, and let it cool down **180** seconds = 3 minutes.
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SHT31 version 0.3.3 and up guards the cool down time by preventing switching the heater on
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within **180** seconds of the last switch off. Note: this guarding is not reboot persistent.
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**WARNING:** The user is responsible to switch the heater off manually!
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The class does **NOT** do this automatically.
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Switch off the heater by directly calling **heatOff()** or indirectly by calling **isHeaterOn()**.
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- **void setHeatTimeout(uint8_t seconds)** Set the time out of the heat cycle.
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This value is truncated to max 180 seconds.
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- **uint8_t getHeatTimeout
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- **bool heatOn()** switches heat cycle on if not already on.
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Returns false if fails, setting error to **SHT31_ERR_HEATER_COOLDOWN**
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or to **SHT31_ERR_HEATER_ON**.
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- **bool heatOff()** switches heat cycle off.
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Returns false if fails, setting error to **SHT31_ERR_HEATER_OFF**.
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- **bool isHeaterOn()** is the sensor still in heating cycle? replaces **heatUp()**.
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Will switch the heater off if max heating time has passed.
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- **bool heatUp()** will be obsolete in the future. replaced by **isHeaterOn()**
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#### Async interface
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See async example for usage
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- **bool requestData()** requests a new measurement. Returns false if this fails.
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- **bool dataReady()** checks if enough time has passed to read the data. (15 milliseconds)
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- **bool readData(bool fast = true)** fast = true skips the CRC check.
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Returns false if reading fails or in case of a CRC failure.
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## Status fields
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| BIT | Description | value | notes |
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|:------|:-----------------------------|:--------|:--------|
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| 15 | Alert pending status | 0 | no pending alerts
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| | | 1 | at least one pending alert - default
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| 14 | Reserved | 0 |
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| 13 | Heater status | 0 | Heater OFF - default
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| | | 1 | Heater ON
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| 12 | Reserved | 0 |
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| 11 | Humidity tracking alert | 0 | no alert - default
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| | | 1 | alert
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| 10 | Temperature tracking alert | 0 | no alert - default
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| | | 1 | alert
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| 9-5 | Reserved | 00000 |
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| 4 | System reset detected | 0 | no reset since last <20>clear status register<65> command
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| | | 1 | reset detected (hard or soft reset command or supply fail) - default
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| 3-2 | Reserved | 00 |
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| 1 | Command status | 0 | last command executed successfully
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| | | 1 | last command not processed. Invalid or failed checksum
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| 0 | Write data checksum status | 0 | checksum of last write correct
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| | | 1 | checksum of last write transfer failed
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## Future
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#### Must
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- keep in sync with (leading) SHT31 library
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- remove script for atomic if not needed any more.
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#### Should
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#### Could
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#### Wont
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