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177 lines
5.8 KiB
Markdown
177 lines
5.8 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/DHT20/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/DHT20/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/DHT20/blob/master/LICENSE)
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[](https://github.com/RobTillaart/DHT20/releases)
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# DHT20
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Arduino library for I2C DHT20 temperature and humidity sensor.
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## Description
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The library must be initiated by calling the **begin()** function,
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or **begin(dataPin, clockPin)** for **ESP32** and similar platforms.
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Thereafter one has to call the **read()** function to do the actual reading,
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and with **getTemperature()** and **getHumidity()** to get the measured values.
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Calling these latter again will return the same values until a new **read()** is called.
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The **read()** call of this sensor is blocking for 80+ milliseconds (datasheet 7.4)
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so the library also has a asynchronous interface. See below.
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Since 0.1.3 and 0.1.4 the performance of **read()** has been optimized,
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still blocking but less long for about 45 milliseconds.
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### Connection
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Always check datasheet
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Front view
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```
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+--------------+
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VDD ----| 1 |
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SDA ----| 2 DHT20 |
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GND ----| 3 |
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SCL ----| 4 |
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+--------------+
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```
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### Tested
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Verified to work with Arduino UNO and ESP32.
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Please let me know if other platforms work (or not).
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## Interface
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### Constructor
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- **DHT20(TwoWire \*wire = &Wire)** constructor, using a specific Wire (I2C bus).
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- **bool begin(uint8_t dataPin, uint8_t clockPin)** begin for ESP32 et al, to set I2C bus pins.
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- **bool begin()** initializer for non ESP32. Returns true if connected.
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- **bool isConnected()** returns true if the address of the DHT20 can be seen on the I2C bus.
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### Core
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- **int8_t read()** read the sensor and store the values internally.
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It returns the status of the read which should be 0.
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- **float getHumidity()** returns last Humidity read.
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- **float getTemperature()** returns last Temperature read.
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### Offset
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- **void setHumOffset(float offset)** set an offset to calibrate (1st order) the sensor.
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- **float getHumOffset()** return current offset, default 0.
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- **void setTempOffset(float offset)** set an offset to calibrate (1st order) the sensor.
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- **float getTempOffset()** return current offset, default 0.
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### Asynchronous interface
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There are two timings that need to be considdered,
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- time between requests = 1000 ms
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- time between request and data ready = 80 ms
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The async interface allows one to continue processing after a **requestData()** has been made.
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Note that there should be at least **1000 milliseconds** between subsequent requests.
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With **bool isMeasuring()** one can check if a new measurement is ready.
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If so the sensor can be read with **readData()**.
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To interpret the read bits to temperature, humidity and status one needs to call **convert()** as last step.
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- **int requestData()** signals the sensor to make a new measurement.
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Note there must be at least 1000 milliseconds between requests!
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- **int readData()** does the actual reading of the data.
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- **int convert()** converts the read bits to temperature and humidity.
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See the example **DHT20_async.ino**
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### Status
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- **uint8_t readStatus()** forced read of the status only.
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This function blocks a few milliseconds to optimize communication.
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- **bool isCalibrated()** idem, wrapper around **readStatus()**
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- **bool isMeasuring()** idem, wrapper around **readStatus()**
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- **bool isIdle()** idem, wrapper around **readStatus()**
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- **int internalStatus()** returns the internal status of the sensor. (for debug).
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| status bit | meaning |
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|:------------:|:---------------------------|
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| 7 | 1 = measurement, 0 = idle |
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| 6 - 4 | unknown |
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| 3 | 1 = calibrated, 0 = not |
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| 2 - 0 | unknown |
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#### Experimental 0.1.4 resetSensor
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Use with care, as this is not tested.
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- **uint8_t resetSensor()** if at startup the sensor does not return a status of 0x18,
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three registers 0x1B, 0x1C and 0x1E need to be reset.
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See datasheet 7.4 Sensor Reading Process, point 1.
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There is no documentation about the meaning of these registers.
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The code is based upon example code for the AHT20 (from manufacturer).
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### Timing
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- **uint32_t lastRead()** last time the sensor is read in milliseconds since start.
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- **uint32_t lastRequest()** last time a request is made to make a measurement.
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### Return codes
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| name | value | notes |
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|:----------------------------|:-------:|:--------|
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| DHT20_OK | 00 | OK
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| DHT20_ERROR_CHECKSUM | -10 | values might be OK if they are like recent previous ones.
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| DHT20_ERROR_CONNECT | -11 | check connection
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| DHT20_MISSING_BYTES | -12 | check connection
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| DHT20_ERROR_BYTES_ALL_ZERO | -13 | check connection
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| DHT20_ERROR_READ_TIMEOUT | -14 |
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| DHT20_ERROR_LASTREAD | -15 | wait 1 second between reads
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## Operation
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See examples
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## Future
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#### must
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#### should
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#### could
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- improve unit tests.
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- investigate
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- sensor calibration (website aosong?)
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- investigate optimizing timing in readStatus()
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- delay(1) ==> microSeconds(???).
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- separate changelog.md
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- connected flag?
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#### won't
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- **void setIgnoreChecksum(bool = false)** ignore checksum flag speeds up communication a bit
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- **bool getIgnoreChecksum()** get checksum flag. for completeness.
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-
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