sht1x: add a new sht1x sensor

samples/sht1x.go

@@ -0,0 +1,60 @@
+// +build ignore
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"os/signal"
+	"time"
+
+	"github.com/kidoman/embd"
+	"github.com/kidoman/embd/sensor/sht1x"
+
+	_ "github.com/kidoman/embd/host/all"
+)
+
+func main() {
+	flag.Parse()
+
+	if err := embd.InitGPIO(); err != nil {
+		panic(err)
+	}
+	defer embd.CloseGPIO()
+
+	data, err := embd.NewDigitalPin(4)
+	if err != nil {
+		panic(err)
+	}
+	defer data.Close()
+
+	clock, err := embd.NewDigitalPin(3)
+	if err != nil {
+		panic(err)
+	}
+	defer clock.Close()
+
+	sensor := sht1x.New(data, clock)
+
+	quit := make(chan os.Signal, 1)
+	signal.Notify(quit, os.Interrupt, os.Kill)
+	defer signal.Stop(quit)
+
+	ticker := time.NewTicker(2 * time.Second)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ticker.C:
+			m, err := sensor.Measure()
+			if err != nil {
+				fmt.Printf("err: %v\n", err)
+			}
+			fmt.Printf("Temperature: %.1fC, Relative Humidity: %.1f%%, Dew Point: %.1fC\n", m.Temperature, m.RelativeHumidity, m.DewPoint)
+
+		case <-quit:
+			return
+		}
+	}
+}

sensor/sht1x/sht1x.go

@@ -0,0 +1,298 @@
+// Package sht1x allows interfacing with Sensirion SHT1x family of humidity
+// and temperature sensors.
+package sht1x
+
+import (
+	"errors"
+	"math"
+	"sync"
+	"time"
+
+	"github.com/kidoman/embd"
+)
+
+// Constants and implementation derived from
+// http://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/Humidity/Sensirion_Humidity_SHT1x_Datasheet_V5.pdf
+const (
+	d1                        = -40.1
+	d2                        = 0.01
+	c1                        = -2.0468
+	c2                        = 0.0367
+	c3                        = -0.0000015955
+	t1                        = 0.01
+	t2                        = 0.00008
+	tnA0                      = 243.12
+	mA0                       = 17.62
+	tnB0                      = 272.62
+	mB0                       = 22.46
+	measureTemperatureCommand = 3
+	measureHumidityCommand    = 5
+)
+
+// Measurement represents a measurement of temperature in degrees Celsius,
+// relative humidity in percent, and dew point in degrees Celsius.
+type Measurement struct {
+	Temperature      float64
+	RelativeHumidity float64
+	DewPoint         float64
+}
+
+// SHT1x represents a SHT1x humidity and temperature sensor.
+type SHT1x struct {
+	DataPin, ClockPin embd.DigitalPin
+	m                 sync.RWMutex
+}
+
+// New returns a handle to a SHT1x sensor.
+func New(dataPin, clockPin embd.DigitalPin) *SHT1x {
+	return &SHT1x{
+		DataPin:  dataPin,
+		ClockPin: clockPin,
+	}
+}
+
+// Measure returns a Measurement with temperature in degrees Celsius,
+// relative humidity in percent, and dew point in degrees Celsius.
+func (d *SHT1x) Measure() (*Measurement, error) {
+	rawTemperature, err := d.rawTemperature()
+	if err != nil {
+		return nil, err
+	}
+
+	rawHumidity, err := d.rawHumidity()
+	if err != nil {
+		return nil, err
+	}
+
+	temperature := temperatureFromRaw(rawTemperature)
+	relativeHumidity := humidityFromRaw(rawHumidity, temperature)
+	dewPoint := calculateDewPoint(relativeHumidity, temperature)
+
+	measurement := &Measurement{
+		Temperature:      temperature,
+		RelativeHumidity: relativeHumidity,
+		DewPoint:         dewPoint,
+	}
+
+	return measurement, nil
+}
+
+// Temperature returns a temperature measurement in degrees Celsius.
+func (d *SHT1x) Temperature() (float64, error) {
+	raw, err := d.rawTemperature()
+	if err != nil {
+		return 0, err
+	}
+
+	temperature := temperatureFromRaw(raw)
+
+	return temperature, nil
+}
+
+// RelativeHumidity returns a relative humidity measurement in percent.
+func (d *SHT1x) RelativeHumidity() (float64, error) {
+	rawTemperature, err := d.rawTemperature()
+	if err != nil {
+		return 0, err
+	}
+
+	rawHumidity, err := d.rawHumidity()
+	if err != nil {
+		return 0, err
+	}
+
+	temperature := temperatureFromRaw(rawTemperature)
+	relativeHumidity := humidityFromRaw(rawHumidity, temperature)
+
+	return relativeHumidity, nil
+}
+
+// DewPoint returns a dew point measurement in degrees Celsius.
+func (d *SHT1x) DewPoint() (float64, error) {
+	rawTemperature, err := d.rawTemperature()
+	if err != nil {
+		return 0, err
+	}
+
+	rawHumidity, err := d.rawHumidity()
+	if err != nil {
+		return 0, err
+	}
+
+	temperature := temperatureFromRaw(rawTemperature)
+	relativeHumidity := humidityFromRaw(rawHumidity, temperature)
+
+	dewPoint := calculateDewPoint(relativeHumidity, temperature)
+	return dewPoint, nil
+}
+
+func (d *SHT1x) sendCommand(command int) error {
+	d.DataPin.SetDirection(embd.Out)
+	d.ClockPin.SetDirection(embd.Out)
+
+	d.DataPin.Write(embd.High)
+	d.ClockPin.Write(embd.High)
+	d.DataPin.Write(embd.Low)
+	d.ClockPin.Write(embd.Low)
+	d.ClockPin.Write(embd.High)
+	d.DataPin.Write(embd.High)
+	d.ClockPin.Write(embd.Low)
+
+	for i := 0; i < 8; i++ {
+		bitSet := (command&(1<<uint(7-i)) != 0)
+		bit := 0
+		if bitSet {
+			bit = 1
+		}
+		d.DataPin.Write(bit)
+		d.ClockPin.Write(embd.High)
+		d.ClockPin.Write(embd.Low)
+	}
+
+	d.DataPin.SetDirection(embd.In)
+
+	d.ClockPin.Write(embd.High)
+	ack, err := d.DataPin.Read()
+	if err != nil {
+		return err
+	}
+	if ack != embd.Low {
+		return errors.New("sht1x: command not acknowledged")
+	}
+
+	d.ClockPin.Write(embd.Low)
+	ack, err = d.DataPin.Read()
+	if err != nil {
+		return err
+	}
+	if ack != embd.High {
+		return errors.New("sht1x: command not acknowledged")
+	}
+
+	return nil
+}
+
+func (d *SHT1x) waitForResult() error {
+	d.DataPin.SetDirection(embd.In)
+
+	for i := 0; i < 100; i++ {
+		time.Sleep(10 * time.Millisecond)
+		ack, err := d.DataPin.Read()
+		if err != nil {
+			return err
+		}
+		if ack == embd.Low {
+			return nil
+		}
+	}
+
+	return errors.New("sht1x: timeout waiting for result")
+}
+
+func (d *SHT1x) getData() int {
+	highByte := d.readByte()
+
+	d.sendReadAck()
+
+	lowByte := d.readByte()
+
+	d.skipCrc()
+
+	temp := highByte * 256
+	temp = temp | lowByte
+
+	return temp
+}
+
+func (d *SHT1x) readByte() int {
+	d.ClockPin.SetDirection(embd.Out)
+	d.DataPin.SetDirection(embd.In)
+
+	readByte := 0
+	for i := 0; i < 8; i++ {
+		d.ClockPin.Write(embd.High)
+		val, _ := d.DataPin.Read()
+		readByte = readByte*2 + val
+		d.ClockPin.Write(embd.Low)
+	}
+	return readByte
+}
+
+func (d *SHT1x) sendReadAck() {
+	d.ClockPin.SetDirection(embd.Out)
+	d.DataPin.SetDirection(embd.Out)
+
+	d.DataPin.Write(embd.High)
+	d.DataPin.Write(embd.Low)
+	d.ClockPin.Write(embd.High)
+	d.ClockPin.Write(embd.Low)
+}
+
+func (d *SHT1x) skipCrc() {
+	d.DataPin.SetDirection(embd.Out)
+	d.ClockPin.SetDirection(embd.Out)
+
+	d.DataPin.Write(embd.High)
+	d.ClockPin.Write(embd.High)
+	d.ClockPin.Write(embd.Low)
+}
+
+func (d *SHT1x) rawTemperature() (float64, error) {
+	d.m.Lock()
+	defer d.m.Unlock()
+
+	err := d.sendCommand(measureTemperatureCommand)
+	if err != nil {
+		return 0, err
+	}
+
+	err = d.waitForResult()
+	if err != nil {
+		return 0, err
+	}
+
+	data := d.getData()
+
+	return float64(data), nil
+}
+
+func (d *SHT1x) rawHumidity() (float64, error) {
+	d.m.Lock()
+	defer d.m.Unlock()
+
+	err := d.sendCommand(measureHumidityCommand)
+	if err != nil {
+		return 0, err
+	}
+
+	err = d.waitForResult()
+	if err != nil {
+		return 0, err
+	}
+
+	data := d.getData()
+
+	return float64(data), nil
+}
+
+func temperatureFromRaw(rawTemperature float64) float64 {
+	return d1 + d2*rawTemperature
+}
+
+func humidityFromRaw(rawHumidity, temperature float64) float64 {
+	linearHumidity := c1 + c2*rawHumidity + c3*rawHumidity*rawHumidity
+	relativeHumidity := (temperature-25)*(t1+t2*rawHumidity) + linearHumidity
+	return relativeHumidity
+}
+
+func calculateDewPoint(humidity, temperature float64) float64 {
+	tn := tnB0
+	m := mB0
+
+	if temperature > 0 {
+		tn = tnA0
+		m = mA0
+	}
+
+	return tn * (math.Log(humidity/100.0) + (m*temperature)/(tn+temperature)) / (m - math.Log(humidity/100.0) - m*temperature/(tn+temperature))
+}