GY-63_MS5611/libraries/CHT8305

CHT8305

Arduino library for CHT8305 temperature and humidity sensor.

EXPERIMENTAL minimal tested.

If you are able to test this library, please let me know your experiences.

Description

The CHT8305 is a temperature and humidity sensor.

sensor	range	accuracy*	resolution
temperature	-40°..125°	max 2°C	0.1° C
humidity	0%..100% RH	max 5% RH	0.1% RH

* Accuracy for full range. More exact details for smaller ranges, see datasheet (page 8).

One of the interesting functions is the support of an ALERT function. This prevents the need for continuous polling of the sensor.

0.2.0 Breaking change

Version 0.2.0 introduced a breaking change. You cannot set the pins in begin() any more. This reduces the dependency of processor dependent Wire implementations. The user has to call Wire.begin() and can optionally set the Wire pins before calling begin().

Moved the address parameter from begin() to constructor.

Tests

• Temperature and humidity functions works on AVR.
  • default about 14 milliseconds at 14 bit resolution.
• offset functions work.
• getVoltage() function works on AVR but meaning unclear.
• getManufacturer(), getVersionID() works on AVR.

The ALERT functions are not tested. The reason is that the sensor I have does not expose the ALERT pin.

If you are able to test the ALERT functions, please let me know your experiences.

Hardware

Always check datasheet for connections.

//
//             +---------------+
//     VCC ----| VCC           |
//     SDA ----| SDA  CHT8305  |
//     GND ----| GND           |
//     SCL ----| SCL           |
//      ?  ----| AD0           |   ? depends on address see table below.
//             |               |
//     IRQ ----| ALERT         |   only if enabled.
//             +---------------+
//
//  check datasheet
//  VCC     RED
//  GND     BLACK
//  SDA     YELLOW
//  SCL     WHITE

Pull ups are needed on SDA, SCL and optional to ALERT.

Alert

The CHT8305 has an ALERT logic output pin with an open drain structure. This output is active low. (if the breakout supports this.)

I2C

performance

I2C bus speeds is supported up to 400 kHz. In practice the sensor seems to work even at 800 kHz. However not clear if the higher speed brings extra wear?

As the sensor / library blocks on reading the temperature using high I2C speeds does not make a difference, except for reading Humidity.

So a higher I2C speed does not help to read this sensor.

See - HT8305_performance.ino

SPEED	READ	READ_T	READ_H
100000	14824	14604	376
200000	14476	14360	224
300000	14368	14276	172
400000	14324	14244	148
500000	14300	14224	140
600000	14276	14212	132
700000	14272	14204	124
800000	14268	14196	120

Addresses

AD0	Address	Notes
GND	0x40	CHT8305_DEFAULT_ADDRESS
VCC	0x41
SDA	0x42
SCL	0x43

Pull ups are needed on SDA, SCL and optional to ALERT.

I2C multiplexing

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.

• https://github.com/RobTillaart/TCA9548

Interface

#include "CHT8305.h"

Constructor

• CHT8305(const uint8_t address = CHT8305_DEFAULT_ADDRESS, TwoWire *wire = &Wire) Constructor with default address (0x40) and I2C bus.
• int begin() initializes internals. Returns error status.
• bool isConnected() checks if address (default 0x40) can be seen on the I2C bus.

Core

• int read() reads both the temperature and humidity. Can be called once per second.
• int readTemperature() read only temperature (slightly faster than read)
• int readHumidity() read only humidity (slightly faster than read)
• uint32_t lastRead() returns lastRead in MilliSeconds since start sketch. Useful to check when it is time to call read() again, or for logging.
• float getHumidity() returns last humidity read. Will return the same value until read() or readHumidity() is called again.
• float getTemperature() returns last temperature read. Will return the same value until read() or readTemperature() is called again.

Note: read(), readTemperature() and readHumidity() block each other, so you can call only one of them every second.

Conversion delay

• void setConversionDelay(uint8_t cd = 14) default is 14 milliseconds (from the datasheet). 7 milliseconds failed and 8 milliseconds worked. So values below 8 milliseconds are mapped to 8 in the library. Expect that 10 milliseconds is a pretty save value to work with. Adjust this setting at your own risk. It might be that lower resolutions allow shorter delays. This is not tested.
• uint8_t getConversionDelay() returns the default (14) or last set value.

Offset

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 since 0.1.7).

• void setHumidityOffset(float offset = 0.0) idem. Default is set to zero, for an easy reset off the offset. There is no range check in this function, however, read() will keep the value between 0 and 100%.
• void setTemperatureOffset(float offset = 0.0) idem. Default is set to zero, for an easy reset off the offset. There is no range check in this function.
• float getHumidityOffset() idem.
• float getTemperatureOffset() idem.

If the offset is not the same over the operational range, consider a mapping function for temperature and humidity. e.g. https://github.com/RobTillaart/MultiMap

Configuration register

Check the datasheet for details of the register bits.

• bool setConfigRegister(uint16_t bitmask) See table below. Default value 0x1004. Returns false if write to the config register fails. Check getLastError() for possible cause.
• uint16_t getConfigRegister() idem. If 0x0000 is returned it may indicate an error. Check getLastError() for possible cause.

Bits of configRegister, check datasheet for details.

bit	mask	name	description
15	0x8000	soft reset	1 = reboot the sensor to default
14	0x4000	clock stretch	1 = ON, 0 = OFF (default)
13	0x2000	heater	1 = ON, 0 = OFF (default)
12	0x1000	mode	1 = read both (default), 0 = read T or RH
11	0x0800	vccs	1 = >2.8V, 0 = <2.8V
10	0x0400	T-RES	1 = 11 bit, 0 = 14 bit (default)
9-8	0x0300	H-RES	10 = 8 bit, 01 = 11 bit, 00 = 14 bit (default)
7-6	0x00C0	ALTM	Alert Mode (datasheet)
5	0x0020	APS	Alert pending status
4	0x0010	H-ALT	Humidity Alert status
3	0x0008	T-ALT	Temperature Alert status
2	0x0004	VCC enable	1 = enable VCC measurement (default), 0 = disable
1-0	0x0003	reserved.	do not change.

Getters / setters configuration register

Note: setting setConfigRegister(bitmask) can be faster.

Wrapper functions for easy configuration. Read the datasheet for the details.

• void softReset() sets the soft reset bit in the configuration, causing the sensor to reset.
• void setI2CClockStretch(bool on = false) check datasheet.
• bool getI2CClockStretch() check datasheet.
• void setHeaterOn(bool on = false) switch on internal heater. Can improve humidity readings. See datasheet for (limited) details.
  • WARNING User is responsible for timing as library does not support timing.
• bool getHeater() Returns status of the heater.
• void setMeasurementMode(bool both = true) both T and H or single value.
• bool getMeasurementMode() returns mode set above.
• bool getVCCstatus() 1 == > 2.8V 0 == < 2.8V Useful when battery operated?
• void setTemperatureResolution(uint8_t res = 0) 1 = 11 bit, 0 = 14 bit (default).
• uint8_t getTemperatureResolution() idem.
• void setHumidityResolution(uint8_t res = 0) 2 = 8 bit, 1 = 11 bit, 0 = 14 bit (default).
• uint8_t getHumidityResolution() idem.
• void setVCCenable(bool enable = false) enable VCC measurement of the power supply.
• bool getVCCenable() return current status of enable bit.

Alert

See register 3 datasheet page 12 for details.

• void setAlertTriggerMode(uint8_t mode = 0) see table below.
• uint8_t getAlertTriggerMode() returns 0, 1, 2 or 3.

mode	trigger	notes
0	T or H	default
1	T
2	H
3	T and H

• bool getAlertPendingStatus() idem.
• bool getAlertHumidityStatus() idem.
• bool getAlertTemperatureStatus() idem.
• bool setAlertLevels(float temperature, float humidity)
  • the values will be truncated to the nearest value possible.
  • the ALERT supports HIGH limit only ==> there is no LOW limit ALERT.
  • note: the datasheet is ambiguous with respect to the formula used.
• float getAlertLevelTemperature() returns the truncated value set.
• float getAlertLevelHumidity() returns the truncated value set.

The ALERT pin triggers with a falling edge (from HIGH to LOW).

Supply voltage

(datasheet 1.1.5) The chip has a feature to measure supply voltage (VCC) with 16bit output data. VCC measurement should be enabled by means of void setVCCenable(true).

• float getVoltage() unclear what unit is used.

Best guess for now: 16 bit data implies voltage = 5.0V * value / 32767.0; Varied slightly 5.000 - 4.999 also for 3V3 power supply.

Conclusion: it is not 100 % clear how to interpret this register.

Meta data

• uint16_t getManufacturer() returns 0x5959.
• uint16_t getVersionID() return value may differ. Test returned 0x8305.

Error handling

Since 0.2.2 some error handling has been added. This need to be improved in the future.

• getLastError() returns 0 if all is OK. If it doesn't return 0 an error occurred during read() et al. The table gives some information where the problem occurred. A call to getLastError() resets the internal error flag.

Note: in case of e.g. an I2C error, the last values of Temperature and Humidity do not change.

Error constant	value	Notes
CHT8305_OK	0
CHT8305_ERROR_ADDR	-10
CHT8305_ERROR_I2C	-11
CHT8305_ERROR_CONNECT	-12
CHT8305_ERROR_BUFSIZE	-13
CHT8305_ERROR_LASTREAD	-20
CHT8305_ERROR_GENERIC	-999
	0xFFFF	patch

Register map

See datasheet page 10 for details

Address	Register name
0x00	CHT8305_REG_TEMPERATURE
0x01	CHT8305_REG_HUMIDITY
0x02	CHT8305_REG_CONFIG
0x03	CHT8305_REG_ALERT
0x04	CHT8305_REG_VOLTAGE
0xFE	CHT8305_REG_MANUFACTURER
0xFF	CHT8305_REG_VERSION

Future

Must

• elaborate documentation.

Should

• test other platforms
  • ESP32,
• test resolution bits.
  • delay ?
• test configuration functions.
• test ALERT functions.
• test write / readRegister with a single uint16_t to simplify code.
• test error handling.

Could

• parameter testing
• parameter defaults?
• investigate asynchronous reading
  • request, ready (after 15 millis), fetch
  • needs lastRequest timestamp
• configRegister => force bit 0 and 1 to 0

Wont

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