tinygo.org/x/drivers@v0.27.1-0.20240509133757-7dbca2a54349/sht4x/sht4x.go (about)

     1  // Package sht4x provides a driver for the SHT4x digital humidity sensor series by Sensirion.
     2  // Datasheet: https://www.sensirion.com/media/documents/33FD6951/64D3B030/Sensirion_Datasheet_SHT4x.pdf
     3  package sht4x
     4  
     5  import (
     6  	"time"
     7  
     8  	"tinygo.org/x/drivers"
     9  )
    10  
    11  const DefaultAddress = 0x44
    12  
    13  const (
    14  	// single-shot, high-repeatability measurement
    15  	commandMeasurement = 0xfd
    16  )
    17  
    18  // Device represents a SHT4x sensor
    19  type Device struct {
    20  	bus     drivers.I2C
    21  	Address uint8
    22  }
    23  
    24  // New creates a new SHT4x connection. The I2C bus must already be
    25  // configured.
    26  func New(bus drivers.I2C) Device {
    27  	return Device{
    28  		bus:     bus,
    29  		Address: DefaultAddress,
    30  	}
    31  }
    32  
    33  // ReadTemperatureHumidity starts a measurement and then reads out the results. This function blocks
    34  // while the measurement is in progress.
    35  //
    36  // Temperature is returned in [degree Celsius], multiplied by 1000,
    37  // and relative humidity in [percent relative humidity], multiplied by 1000.
    38  func (d *Device) ReadTemperatureHumidity() (temperatureMilliCelsius int32, relativeHumidityMilliPercent int32, err error) {
    39  	rawTemp, rawHum, err := d.rawReadings()
    40  	if err != nil {
    41  		return 0, 0, err
    42  	}
    43  
    44  	// from the reference driver: https://github.com/Sensirion/embedded-sht/blob/fcc8a523210cc1241a2750899ff6b0f68f3ed212/sht4x/sht4x.c#L81
    45  	temperatureMilliCelsius = ((21875 * int32(rawTemp)) >> 13) - 45000
    46  	relativeHumidityMilliPercent = ((15625 * int32(rawHum)) >> 13) - 6000
    47  
    48  	return temperatureMilliCelsius, relativeHumidityMilliPercent, err
    49  }
    50  
    51  // rawReadings returns the sensor's raw values of the temperature and humidity
    52  func (d *Device) rawReadings() (uint16, uint16, error) {
    53  	err := d.bus.Tx(uint16(d.Address), []byte{commandMeasurement}, nil)
    54  	if err != nil {
    55  		return 0, 0, err
    56  	}
    57  
    58  	// max time for measurement according to datasheet
    59  	time.Sleep(10 * time.Millisecond)
    60  
    61  	var data [6]byte
    62  	err = d.bus.Tx(uint16(d.Address), nil, data[:])
    63  	if err != nil {
    64  		return 0, 0, err
    65  	}
    66  
    67  	tTicks := readUint(data[0], data[1])
    68  	rhTicks := readUint(data[3], data[4])
    69  
    70  	return tTicks, rhTicks, nil
    71  }
    72  
    73  // readUint converts two bytes to uint16
    74  func readUint(msb byte, lsb byte) uint16 {
    75  	return (uint16(msb) << 8) | uint16(lsb)
    76  }