SHT3x driver (#53)

* SHT3x driver

sht3x/registers.go

@@ -0,0 +1,15 @@
+package sht3x
+
+// Constants/addresses used for I2C.
+
+// The I2C address which this device listens to.
+const (
+	AddressA = 0x44
+	AddressB = 0x45
+)
+
+const (
+	// single shot, high repeatability
+	MEASUREMENT_COMMAND_MSB = 0x24
+	MEASUREMENT_COMMAND_LSB = 0x00
+)

sht3x/sht3x.go

@@ -0,0 +1,72 @@
+// Package sht3x provides a driver for the SHT3x digital humidity sensor
+// series by Sensirion.
+//
+// Datasheet:
+// https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/0_Datasheets/Humidity/Sensirion_Humidity_Sensors_SHT3x_Datasheet_digital.pdf
+//
+package sht3x
+
+import (
+	"machine"
+	"time"
+)
+
+// Device wraps an I2C connection to a SHT31 device.
+type Device struct {
+	bus     machine.I2C
+	Address uint16
+}
+
+// New creates a new SHT31 connection. The I2C bus must already be
+// configured.
+//
+// This function only creates the Device object, it does not initialize the device.
+// You must call Configure() first in order to use the device itself.
+func New(bus machine.I2C) Device {
+	return Device{
+		bus:     bus,
+		Address: AddressA,
+	}
+}
+
+// Read returns the temperature in celsius milli degrees (ºC/1000).
+func (d *Device) ReadTemperature() (tempMilliCelsius int32, err error) {
+	tempMilliCelsius, _, err = d.ReadTemperatureHumidity()
+	return tempMilliCelsius, err
+}
+
+// Read returns the relative humidity in hundredths of a percent.
+func (d *Device) ReadHumidity() (relativeHumidity int16, err error) {
+	_, relativeHumidity, err = d.ReadTemperatureHumidity()
+	return relativeHumidity, err
+}
+
+// Read returns both the temperature and relative humidity.
+func (d *Device) ReadTemperatureHumidity() (tempMilliCelsius int32, relativeHumidity int16, err error) {
+	var rawTemp, rawHum, errx = d.rawReadings()
+	if errx != nil {
+		err = errx
+		return
+	}
+	tempMilliCelsius = (35000 * int32(rawTemp) / 13107) - 45000
+	relativeHumidity = int16(2000 * int32(rawHum) / 13107)
+	return tempMilliCelsius, relativeHumidity, err
+}
+
+// rawReadings returns the sensor's raw values of the temperature and humidity
+func (d *Device) rawReadings() (uint16, uint16, error) {
+	d.bus.Tx(d.Address, []byte{MEASUREMENT_COMMAND_MSB, MEASUREMENT_COMMAND_LSB}, nil)
+
+	time.Sleep(17 * time.Millisecond)
+
+	var data [5]byte
+	d.bus.Tx(d.Address, []byte{}, data[:])
+	// ignore crc for now
+
+	return readUint(data[0], data[1]), readUint(data[3], data[4]), nil
+}
+
+// readUint converts two bytes to uint16
+func readUint(msb byte, lsb byte) uint16 {
+	return (uint16(msb) << 8) | uint16(lsb)
+}