Arduino library for CHT832X temperature and humidity sensor.
Experimental
The CHT8320 and CHT8325 are temperature and relative humidity sensors. They both have the same interface, the CHT8325 is slightly more accurate. The CHT832X are factory calibrated and have an unique NIST number (48 bit) to be globally trackable.
This library implements the most important functionality of the sensor. This includes reading the temperature and humidity and the manufacturer-ID register. Furthermore one can set an offset for temperature and humidity.
The API of the library is based upon https://github.com/RobTillaart/CHT8310 The sensors use a different protocol to communicate.
The library is tested to work with hardware, see issue 3.
Feedback as always is welcome, please share your experiences.
Fixed CRC for humidity - see #9
Fixed temperature above 40 degrees Celsius - see #5
The 0.1.0 version was not working, it is now obsolete.
The 0.2.0 version implements an asynchronous interface as one has to wait 60 ms before one can read temperature and humidity. This included a refactor of the low level (private) parts.
- https://github.com/RobTillaart/Temperature (e.g. heatIndex)
- https://github.com/RobTillaart/CHT8305
- https://github.com/RobTillaart/CHT8310
- https://github.com/RobTillaart/CHT832X
- https://github.com/RobTillaart/SHT31 - sort of command compatible!
Always check datasheet for connections.
//
// +---------------+
// VCC ----| VCC |
// SDA ----| SDA CHT832X |
// GND ----| GND |
// SCL ----| SCL |
// +---------------+
//Pull ups are needed on SDA, SCL.
I2C bus speeds is supported up to 1000 KHz (datasheet P4).
An indicative table of times in micros on an UNO R3 for various I2C clock speeds. Note that the performance gain of higher clock speeds become less and less. At the same time the robustness of the signal decreases (not visible in the table).
TODO: fill table
| Version | Speed | Read | getManufacturer |
|---|---|---|---|
| 0.4.0 | 50000 | ||
| 0.4.0 | 100000 | ||
| 0.4.0 | 200000 | ||
| 0.4.0 | 300000 | ||
| 0.4.0 | 400000 | ||
| 0.4.0 | 600000 | ||
| 0.4.0 | 800000 |
The CHT8320 supports one fixed address, however one can order different versions with different addresses. Max 4 sensors per bus.
CHT8320-A-DNR .. CHT8320-D-DNR == 0x44 ..0x47
CHT8325-A-DNR .. CHT8325-D-DNR == 0x44 ..0x47
Pull ups are needed on SDA and SCL.
Sometimes you need to control more devices than possible with the default address range the device provides. This is possible with an I2C multiplexer e.g. TCA9548 which creates up to eight channels (think of it as I2C subnets) which can use the complete address range of the device.
Drawback of using a multiplexer is that it takes more administration in your code e.g. which device is on which channel. This will slow down the access, which must be taken into account when deciding which devices are on which channel. Also note that switching between channels will slow down other devices too if they are behind the multiplexer.
#include "CHT832X.h"- CHT832X(const uint8_t address = CHT832X_DEFAULT_ADDRESS, TwoWire *wire = &Wire) Constructor with default address (0x44) and I2C bus.
- int begin() initializes internals. Returns error status.
- bool isConnected() checks if address (default 0x40) can be seen on the I2C bus.
- uint8_t getAddress() returns address set in constructor.
- int requestData() triggers a new single shot conversion.
- bool dataReady() checks if 60 milliseconds have passed since last request, indicating conversion ready.
- int readData() read the raw data, convert to T & H and store them in cache until next readData() call.
The ASYNC interface will be extended when other acquisition modi are supported. There are continuous modes that work differently.
Note: the read() call wraps the ASYNC interface in a blocking call which lasts for 60 milliseconds.
- int read() reads both the temperature and humidity from the sensor. Can be called at most once per second, otherwise it will return CHT832X_ERROR_LASTREAD Return value should be tested and be CHT832X_OK.
- uint32_t lastRead() returns lastRead in milliSeconds since start sketch. Useful to check when it is time to call read() again, or for logging. LastRead is updated only when read() is successful.
- float getTemperature() returns last temperature read. Will return the same value until read() is called again.
- float getHumidity() returns last humidity read. Will return the same value until read() is called again.
Adding offsets works well in the "normal range" but might introduce under- or overflow at the ends of the sensor range. These are not handled for temperature by the library, humidity is constrained.
- void setHumidityOffset(float offset) idem.
- void setTemperatureOffset(float offset) idem. This function can be used to set return temperature in Kelvin, with offset = 273.15
- float getHumidityOffset() idem.
- float getTemperatureOffset() idem.
If the offset is not the same over the operational range, consider a mapping function for temperature and/or humidity. e.g. https://github.com/RobTillaart/MultiMap
Check datasheet for details.
The heater can be used to remove condense from the sensor - think humidity. It is unclear how long the sensor may be heated. (feedback welcome).
The heater must be disabled when making measurements as the heating affects both the temperature and humidity. Note it might take some time to stabilize to "environment temperature" again.
- void enableHeater() switch on.
- void enableHeaterFull() set to full power level.
- void enableHeaterHalf() set to half power level.
- void enableHeaterQuarter() set to quarter power level.
- void disableHeater() switch off.
The status of the heater can be fetched with getStatusRegister(). see below.
Check datasheet for details.
- uint16_t getStatusRegister() See the table below.
- void clearStatusRegister() idem.
| bit | name | description |
|---|---|---|
| 13 | heater status | 0 = Heater disabled, 1 = heater enabled |
| 4 | reset detected | 0 = no reset, 1 reset since last clearStatus |
| 1 | command status | 0 = executed, 1 = not executed |
| 0 | checksum | 0 = pass, 1 = fail |
| other | reserved |
Check datasheet for details.
- void softwareReset() idem.
In issue RobTillaart/CHT832X#7 it is reported that the CHT8320 does not have an unique NIST identifier (any more). At the moment it is unknown if this is for one manufacturer or for all. Feedback on this topic is welcome.
In short, the getNIST() function is probably not usable to identify your product.
- uint16_t getNIST(uint8_t id) id = 0, 1, 2; returns 2 x 3 = 6 bytes of the device ID. As said above, not guaranteed unique.
- uint16_t getManufacturer() Returns 0x5959 according to the datasheet. Other manufacturers may return different number.
- getError() returns the last error status. Resets internal error to CHT832X_OK.
| value | define | notes |
|---|---|---|
| 0 | CHT832X_OK | default |
| -10 | CHT832X_ERROR_ADDR | |
| -11 | CHT832X_ERROR_I2C | |
| -12 | CHT832X_ERROR_CONNECT | |
| -20 | CHT832X_ERROR_LASTREAD | |
| -21 | CHT832X_ERROR_CRC |
The datasheet states 60 milliseonds is needed for conversion, but some devices might be just slightly faster. So this function allows to gain a few milliseconds. Use with care!
- void setReadDelay(uint8_t rdel = 60) set conversion delay.
- uint8_t getReadDelay() returns set value.
- elaborate documentation.
- buy and test with hardware if all works.
- test heater functions.
- test softwareReset().
- operational modi
- single shot (supported)
- continuous (#samples per second)
- sleep?
- investigate missing functions.
- test different platforms
- AVR, ESP32, ESP8266, STM32, RP2040, ...
- add examples (which functions?)
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