Initial support for SHT2x Temperature/Humidity sensor driver

Signed-off-by: Yoshio HANAWA <[email protected]>

README.md

@@ -283,6 +283,7 @@ drivers provided using the `gobot/drivers/i2c` package:
 	- MPL115A2 Barometer
 	- MPU6050 Accelerometer/Gyroscope
 	- PCA9685 16-channel 12-bit PWM/Servo Driver
+	- SHT2x Temperature/Humidity
 	- SHT3x-D Temperature/Humidity
 	- SSD1306 OLED Display Controller
 	- TSL2561 Digital Luminosity/Lux/Light Sensor

drivers/i2c/README.md

@@ -35,6 +35,7 @@ Gobot has a extensible system for connecting to hardware devices. The following
 - MPL115A2 Barometer
 - MPU6050 Accelerometer/Gyroscope
 - PCA9685 16-channel 12-bit PWM/Servo Driver
+- SHT2x Temperature/Humidity
 - SHT3x-D Temperature/Humidity
 - SSD1306 OLED Display Controller
 - TSL2561 Digital Luminosity/Lux/Light Sensor

drivers/i2c/sht2x_driver.go

@@ -0,0 +1,259 @@
+/*
+ * Copyright (c) 2016-2017 Weston Schmidt <[email protected]>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package i2c
+
+// SHT2xDriver is a driver for the SHT2x based devices.
+//
+// This module was tested with Sensirion SHT21 Breakout.
+
+import (
+	"errors"
+	"time"
+
+	"github.com/sigurn/crc8"
+	"gobot.io/x/gobot"
+)
+
+const (
+	// SHT2xDefaultAddress is the default I2C address for SHT2x
+	SHT2xDefaultAddress = 0x40
+
+	// SHT2xAccuracyLow is the faster, but lower accuracy sample setting
+	//  0/1 = 8bit RH, 12bit Temp
+	SHT2xAccuracyLow = byte(0x01)
+
+	// SHT2xAccuracyMedium is the medium accuracy and speed sample setting
+	//  1/0 = 10bit RH, 13bit Temp
+	SHT2xAccuracyMedium = byte(0x80)
+
+	// SHT2xAccuracyHigh is the high accuracy and slowest sample setting
+	//  0/0 = 12bit RH, 14bit Temp
+	//  Power on default is 0/0
+	SHT2xAccuracyHigh = byte(0x00)
+
+	// SHT2xTriggerTempMeasureHold is the command for measureing temperature in hold master mode
+	SHT2xTriggerTempMeasureHold = 0xe3
+
+	// SHT2xTriggerHumdMeasureHold is the command for measureing humidity in hold master mode
+	SHT2xTriggerHumdMeasureHold = 0xe5
+
+	// SHT2xTriggerTempMeasureNohold is the command for measureing humidity in no hold master mode
+	SHT2xTriggerTempMeasureNohold = 0xf3
+
+	// SHT2xTriggerHumdMeasureNohold is the command for measureing humidity in no hold master mode
+	SHT2xTriggerHumdMeasureNohold = 0xf5
+
+	// SHT2xWriteUserReg is the command for writing user register
+	SHT2xWriteUserReg = 0xe6
+
+	// SHT2xReadUserReg is the command for reading user register
+	SHT2xReadUserReg = 0xe7
+
+	// SHT2xReadUserReg is the command for reading user register
+	SHT2xSoftReset = 0xfe
+)
+
+// SHT2xDriver is a Driver for a SHT2x humidity and temperature sensor
+type SHT2xDriver struct {
+	Units string
+
+	name       string
+	connector  Connector
+	connection Connection
+	Config
+	sht2xAddress int
+	accuracy     byte
+	delay        time.Duration
+	crcTable     *crc8.Table
+}
+
+// NewSHT2xDriver creates a new driver with specified i2c interface
+// Params:
+//		conn Connector - the Adaptor to use with this Driver
+//
+// Optional params:
+//		i2c.WithBus(int):	bus to use with this driver
+//		i2c.WithAddress(int):	address to use with this driver
+//
+func NewSHT2xDriver(a Connector, options ...func(Config)) *SHT2xDriver {
+	// From the document "CRC Checksum Calculation -- For Safe Communication with SHT2x Sensors":
+	crc8Params := crc8.Params{0x31, 0x00, false, false, 0x00, 0x00, "CRC-8/SENSIRION-SHT2x"}
+	s := &SHT2xDriver{
+		Units:     "C",
+		name:      gobot.DefaultName("SHT2x"),
+		connector: a,
+		Config:    NewConfig(),
+		crcTable:  crc8.MakeTable(crc8Params),
+	}
+
+	for _, option := range options {
+		option(s)
+	}
+
+	return s
+}
+
+// Name returns the name for this Driver
+func (d *SHT2xDriver) Name() string { return d.name }
+
+// SetName sets the name for this Driver
+func (d *SHT2xDriver) SetName(n string) { d.name = n }
+
+// Connection returns the connection for this Driver
+func (d *SHT2xDriver) Connection() gobot.Connection { return d.connector.(gobot.Connection) }
+
+// Start initializes the SHT2x
+func (d *SHT2xDriver) Start() (err error) {
+	bus := d.GetBusOrDefault(d.connector.GetDefaultBus())
+	address := d.GetAddressOrDefault(SHT2xDefaultAddress)
+
+	if d.connection, err = d.connector.GetConnection(address, bus); err != nil {
+		return
+	}
+
+	if err = d.Reset(); err != nil {
+		return
+	}
+
+	d.sendAccuracy()
+
+	return
+}
+
+// Halt returns true if devices is halted successfully
+func (d *SHT2xDriver) Halt() (err error) { return }
+
+func (d *SHT2xDriver) Accuracy() byte { return d.accuracy }
+
+// SetAccuracy sets the accuracy of the sampling
+func (d *SHT2xDriver) SetAccuracy(acc byte) (err error) {
+	d.accuracy = acc
+
+	if d.connection != nil {
+		err = d.sendAccuracy()
+	}
+
+	return
+}
+
+// Reset does a software reset of the device
+func (d *SHT2xDriver) Reset() (err error) {
+	if err = d.connection.WriteByte(SHT2xSoftReset); err != nil {
+		return
+	}
+
+	time.Sleep(15 * time.Millisecond) // 15ms delay (from the datasheet 5.5)
+
+	return
+}
+
+// Temperature returns the current temperature, in celsius degrees.
+func (d *SHT2xDriver) Temperature() (temp float32, err error) {
+	var rawT uint16
+	if rawT, err = d.readSensor(SHT2xTriggerTempMeasureNohold); err != nil {
+		return
+	}
+
+	// From the datasheet 6.2:
+	// T[C] = -46.85 + 175.72 * St / 2^16
+	temp = -46.85 + 175.72/65536.0*float32(rawT)
+
+	return
+}
+
+// Humidity returns the current humidity in percentage of relative humidity
+func (d *SHT2xDriver) Humidity() (humidity float32, err error) {
+	var rawH uint16
+	if rawH, err = d.readSensor(SHT2xTriggerHumdMeasureNohold); err != nil {
+		return
+	}
+
+	// From the datasheet 6.1:
+	// RH = -6 + 125 * Srh / 2^16
+	humidity = -6.0 + 125.0/65536.0*float32(rawH)
+
+	return
+}
+
+// sendCommandDelayGetResponse is a helper function to reduce duplicated code
+func (d *SHT2xDriver) readSensor(cmd byte) (read uint16, err error) {
+	if err = d.connection.WriteByte(cmd); err != nil {
+		return
+	}
+
+	//Hang out while measurement is taken. 85ms max, page 9 of datasheet.
+	time.Sleep(85 * time.Millisecond)
+
+	//Comes back in three bytes, data(MSB) / data(LSB) / Checksum
+	buf := make([]byte, 3)
+	counter := 0
+	for {
+		var got int
+		got, err = d.connection.Read(buf)
+		counter++
+		if counter > 50 {
+			return
+		}
+		if err == nil {
+			if got != 3 {
+				err = ErrNotEnoughBytes
+				return
+			}
+			break
+		}
+		time.Sleep(1 * time.Millisecond)
+	}
+
+	//Store the result
+	crc := crc8.Checksum(buf[0:2], d.crcTable)
+	if buf[2] != crc {
+		err = errors.New("Invalid crc")
+		return
+	}
+	read = uint16(buf[0])<<8 | uint16(buf[1])
+	read &= 0xfffc // clear two low bits (status bits)
+
+	return
+}
+
+func (d *SHT2xDriver) sendAccuracy() (err error) {
+	if err = d.connection.WriteByte(SHT2xReadUserReg); err != nil {
+		return
+	}
+	userRegister, err := d.connection.ReadByte()
+	if err != nil {
+		return
+	}
+
+	userRegister &= 0x7e //Turn off the resolution bits
+	acc := d.accuracy
+	acc &= 0x81         //Turn off all other bits but resolution bits
+	userRegister |= acc //Mask in the requested resolution bits
+
+	//Request a write to user register
+	_, err = d.connection.Write([]byte{SHT2xWriteUserReg, userRegister})
+	if err != nil {
+		return
+	}
+
+	userRegister, err = d.connection.ReadByte()
+	if err != nil {
+		return
+	}
+
+	return
+}