GY-63_MS5611/libraries/SHT85/README.md

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# SHT85

Arduino library for the SHT85 temperature and humidity sensor

Based upon the SHT31 library - https://github.com/RobTillaart/SHT31

**Warning:** to keep self-heating below 0.1<EFBFBD>C, the SHT85 sensor should 
not be used for more than 10% of the time.


## Description

```
    // TOPVIEW
    //            +-------+
    // +-----\    | SDA 4 -----
    // | /-+  ----+ VCC 3 -----
    // | +-+  ----+ GND 2 -----
    // +-----/    | SCL 1 -----
    //            +-------+
```

The SHT85 sensors should work up to 1000 KHz, however during tests 
with an Arduino UNO it stopped at ~500 KHz so to be safe I recommend
not to use it above 400 KHz. Also the differences in readtime becomes
quite small. (max 15% gain). See output example sketch.

| I2C speed | read ms | notes |
|:---------:|:-------:|:------|
|  100 KHz  |  5.11   |       |
|  150 KHz  |  4.79   |       |
|  200 KHz  |  4.64   |       |
|  250 KHz  |  4.56   |       |
|  300 KHz  |  4.50   |       |
|  350 KHz  |  4.47   |       |
|  400 KHz  |  4.45   |       |
|  450 KHz  |  4.43   |       |
|  500 KHz  |  4.42   |       |
|  550 KHz  |  ----   | fail  |


### Compatibility

This library should also work for SHT30, SHT31 and SHT35 but 
this is not verified 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 |

Need to investigate if the interface is identical?
If so the libraries might  be merged.


## Interface

#### Base interface

- **SHT85()**  constructor.
- **begin(address, dataPin, clockPin)** begin function for ESP8266 & ESP32; **WARNING: not verified yet**
returns false if device address is incorrect or device cannot be reset.
- **begin(address, TwoWire \*wire = &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()** returns relative humidity in %. Needs a **read()** to update.
- **getTemperature()** returns temperature in <20>C. Needs a **read()** to update.


#### 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 | SHT_OK              | no error                    |
| 0x81 | SHT_ERR_WRITECMD    | I2C write failed            |
| 0x82 | SHT_ERR_READBYTES   | I2C read failed             |
| 0x83 | SHT_ERR_HEATER_OFF  | Could not switch off heater |
| 0x84 | SHT_ERR_NOT_CONNECT | Could not connect           |
| 0x85 | SHT_ERR_CRC_TEMP    | CRC error in temperature    |
| 0x86 | SHT_ERR_CRC_HUM     | CRC error in humidity       |
| 0x87 | SHT_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. (typical 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 <20>clear status register<65> 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

- verify working with ESP32
- merge with other SHT sensors if possible
- investigate command ART (auto sampling at 4 Hz)
- investigate command BREAK (stop auto sampling)
- direct Fahrenheit formula 


## Operation

See examples