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# AM2315C

Arduino library for I2C AM2315C temperature and humidity sensor.


## Description

The AM2315C is a humidity and temperature sensor. 

Warning: this sensor is not compatible with the AM2315.

The sensor has a fixed address of **0x38**.

The library must be initiated by calling the **begin()** function, 
or **begin(dataPin, clockPin)** for **ESP32** and similar platforms.

Thereafter one has to call the **read()** function to do the actual reading,
and call **getTemperature()** and **getHumidity()** to get the measured values.
Calling these latter again will return the same values until a new **read()** is done.

The **read()** call of this sensor is blocking for 80+ milliseconds (datasheet 7.4)
so the library also has a asynchronous interface. See below.

This library is based upon the DHT20 library which is leading in development.
The DHT20 also provides a bit more documentation and issues from the past.
- https://github.com/RobTillaart/DHT20


## I2C

#### Address

The sensor has a fixed address of **0x38**.

To use multiple AM2315C sensors one might use a multiplexer like the
- https://github.com/RobTillaart/TCA9548


#### Connection

Always check datasheet!

Front view
```
                    +-----------------+
    RED    -------- | VDD             |
    YELLOW -------- | SDA    AM2315C  |
    BLACK  -------- | GND             |
    WHITE  -------- | SCL             |
                    +-----------------+
```


## Interface

```cpp
#include "AM2315C.h"
```

#### Constructor

- **AM2315C(TwoWire \*wire = &Wire)** constructor, using a specific Wire (I2C bus).
- **bool begin(uint8_t dataPin, uint8_t clockPin)** begin for ESP32 et al, to set I2C bus pins.
- **bool begin()** initializer for non ESP32. Returns true if connected.
- **bool isConnected()** returns true if the address of the AM2315C can be seen on the I2C bus.
- **uint8_t getAddress()** returns the (fixed) address - convenience.

#### Core

- **int8_t read()** read the sensor and store the values internally. 
Returns the status of the read which should be 0 == **AM2315C_OK**.
- **float getHumidity()** returns last Humidity read.
Multiple calls will return same value until a new **read()** is made.
- **float getTemperature()** returns last Temperature read.
Multiple calls will return same value until a new **read()** is made.


#### Offset

- **void setHumOffset(float offset = 0)** set an offset to calibrate the sensor (1st order).
Default offset is 0.
- **float getHumOffset()** return current humidity offset, default 0.
- **void setTempOffset(float offset = 0)** set an offset to calibrate the sensor (1st order).
Default offset is 0.
- **float getTempOffset()** return current temperature offset, default 0.


#### Asynchronous interface

There are two timings that need to be considered (from datasheet):
- time between requests = 1000 ms.
- time between request and data ready = 80 ms.

The async interface allows one to continue processing after a **requestData()** has been made. 
Note there should be at least **1000 milliseconds** between subsequent requests.

With **bool isMeasuring()** one can check if a new measurement is ready.
Alternative is to delay for up to 80 ms.
If so the sensor can be read with **readData()**.

To interpret the read bits to temperature, humidity and status one needs to call **convert()** as last step.


- **int requestData()** signals the sensor to make a new measurement.
Note there must be at least 1000 milliseconds between requests!
- **int readData()** does the actual reading of the data.
- **int convert()** converts the read bits to temperature and humidity.

See the example **AM2315C_async.ino**


#### Status

- **uint8_t readStatus()** forced read of the status only.
This function blocks a few milliseconds to optimize communication.
- **bool isCalibrated()** idem, wrapper around **readStatus()**
- **bool isMeasuring()** idem, wrapper around **readStatus()**
- **bool isIdle()** idem, wrapper around **readStatus()**
- **int internalStatus()** returns the internal status of the sensor. (for debug).

|  status bit  |  meaning                   |
|:------------:|:---------------------------|
|    7         |  1 = measurement, 0 = idle |
|  6 - 4       |  unknown                   |
|    3         |  1 = calibrated, 0 = not   |
|  2 - 0       |  unknown                   |


#### Experimental resetSensor

Use with care!

- **uint8_t resetSensor()** if at startup the sensor does not return a status of 0x18, 
three registers 0x1B, 0x1C and 0x1E need to be reset. 
See datasheet 7.4 Sensor Reading Process, point 1.
There is no documentation about the meaning of these registers.
The code is based upon example code for the AHT20 (from manufacturer).

The call is needed to get the **read()** working well so it has been embedded into
the read calls. (0.2.0)


#### Timing

- **uint32_t lastRead()** last time the sensor is read in milliseconds since start.
- **uint32_t lastRequest()** last time a request is made to make a measurement.


#### Return codes

|  name                          |  value  |  notes  |
|:-------------------------------|:-------:|:--------|
|  AM2315C_OK                    |    00   |  OK
|  AM2315C_ERROR_CHECKSUM        |   -10   |  values might be OK if they are like recent previous ones.
|  AM2315C_ERROR_CONNECT         |   -11   |  check connection
|  AM2315C_MISSING_BYTES         |   -12   |  check connection
|  AM2315C_ERROR_BYTES_ALL_ZERO  |   -13   |  check connection
|  AM2315C_ERROR_READ_TIMEOUT    |   -14   |
|  AM2315C_ERROR_LASTREAD        |   -15   |  wait 1 second between reads


## Future

#### Must

- improve documentation.
- follow / sync DHT20 developments
  - see https://github.com/RobTillaart/DHT20
- get hardware / sensor to test library

#### Should

#### Could

#### Wont