Added rudiementary support for TH02 Grove Sensor

This commit adds basic support for a TH02 based Grove Sensor which is
silkscreened as

  Temperature&Humidity Sensor (High-Accuracy & Mini ) v1.0

https://www.seeedstudio.com/Grove-Temperature-Humidity-Sensor-High-Accuracy-Min-p-1921.html

This is a modified variant of a SHT2* driver, and still needs some
changes to be more useable.  It is written to assume you want to use the
High Precisions (slow sample rate)

Signed-off-by: npotts <npotts@users.noreply.github.com>

drivers/i2c/th02_driver.go

@@ -0,0 +1,192 @@
+/*
+ * Copyright (c) 2018 Nicholas Potts <nick@the-potts.com>
+ *
+ * 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
+
+// TH02Driver is a driver for the TH02-D based devices.
+//
+// This module was tested with a Grove Temperature and Humidty Sensor (High Accuracy)
+// https://www.seeedstudio.com/Grove-Temperature-Humidity-Sensor-High-Accuracy-Min-p-1921.html
+
+import (
+	"fmt"
+	"time"
+
+	"gobot.io/x/gobot"
+)
+
+// TH02Address is the default address of device
+const TH02Address = 0x40
+
+//TH02ConfigReg is the configuration register
+const TH02ConfigReg = 0x03
+
+// TH02HighAccuracyTemp is the CONFIG write value to start reading temperature
+const TH02HighAccuracyTemp = 0x11
+
+//TH02HighAccuracyRH is the CONFIG write value to start reading high accuracy RH
+const TH02HighAccuracyRH = 0x01
+
+// TH02Driver is a Driver for a TH02 humidity and temperature sensor
+type TH02Driver struct {
+	Units      string
+	name       string
+	connector  Connector
+	connection Connection
+	Config
+	addr     byte
+	accuracy byte
+	delay    time.Duration
+}
+
+// NewTH02Driver 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 NewTH02Driver(a Connector, options ...func(Config)) *TH02Driver {
+	s := &TH02Driver{
+		Units:     "C",
+		name:      gobot.DefaultName("TH02"),
+		connector: a,
+		addr:      TH02Address,
+		Config:    NewConfig(),
+	}
+	//	s.SetAccuracy(TH02AccuracyHigh)
+
+	for _, option := range options {
+		option(s)
+	}
+
+	return s
+}
+
+// Name returns the name for this Driver
+func (s *TH02Driver) Name() string { return s.name }
+
+// SetName sets the name for this Driver
+func (s *TH02Driver) SetName(n string) { s.name = n }
+
+// Connection returns the connection for this Driver
+func (s *TH02Driver) Connection() gobot.Connection { return s.connector.(gobot.Connection) }
+
+// Start initializes the TH02
+func (s *TH02Driver) Start() (err error) {
+	bus := s.GetBusOrDefault(s.connector.GetDefaultBus())
+	address := s.GetAddressOrDefault(int(s.addr))
+
+	s.connection, err = s.connector.GetConnection(address, bus)
+	return err
+}
+
+// Halt returns true if devices is halted successfully
+func (s *TH02Driver) Halt() (err error) { return }
+
+// SetAddress sets the address of the device
+func (s *TH02Driver) SetAddress(address int) { s.addr = byte(address) }
+
+// SerialNumber returns the serial number of the chip
+func (s *TH02Driver) SerialNumber() (sn uint32, err error) {
+	ret, err := s.readRegister(0x11)
+	return uint32(ret) >> 4, err
+}
+
+// Sample returns the temperature in celsius and relative humidity for one sample
+func (s *TH02Driver) Sample() (temp float32, rh float32, err error) {
+	if err := s.writeRegister(TH02ConfigReg, TH02HighAccuracyRH); err != nil {
+		return 0, 0, err
+	}
+
+	rrh, err := s.readData()
+	if err != nil {
+		return 0, 0, err
+	}
+	rrh = rrh >> 4
+	rh = float32(rrh)/16.0 - 24.0
+
+	if err := s.writeRegister(TH02ConfigReg, TH02HighAccuracyTemp); err != nil {
+		return 0, 0, err
+	}
+
+	rt, err := s.readData()
+	if err != nil {
+		return 0, rh, err
+	}
+	rt = rt / 4
+	temp = float32(rt)/32.0 - 50.0
+
+	switch s.Units {
+	case "F":
+		temp = 9.0/5.0 + 32.0
+	}
+
+	return temp, rh, nil
+
+}
+
+// getStatusRegister returns the device status register
+func (s *TH02Driver) getStatusRegister() (status byte, err error) {
+	return s.readRegister(TH02ConfigReg)
+}
+
+//writeRegister writes the value to the register.
+func (s *TH02Driver) writeRegister(reg, value byte) error {
+	_, err := s.connection.Write([]byte{reg, value})
+	return err
+}
+
+//readRegister returns the value of a single regusterm and a non-nil error on problem
+func (s *TH02Driver) readRegister(reg byte) (byte, error) {
+	if _, err := s.connection.Write([]byte{reg}); err != nil {
+		return 0, err
+	}
+	rcvd := make([]byte, 1)
+	_, err := s.connection.Read(rcvd)
+	return rcvd[0], err
+}
+
+func (s *TH02Driver) waitForReady() error {
+	start := time.Now()
+	for {
+		if time.Since(start) > 100*time.Millisecond {
+			return fmt.Errorf("timeout on \\RDY")
+		}
+		reg, _ := s.readRegister(0x00)
+		if reg == 0 {
+			return nil
+		}
+	}
+}
+
+func (s *TH02Driver) readData() (uint16, error) {
+	if err := s.waitForReady(); err != nil {
+		return 1, err
+	}
+
+	if n, err := s.connection.Write([]byte{0x01}); err != nil || n != 1 {
+		return 0, fmt.Errorf("n=%d not 1, or err = %v", n, err)
+	}
+	rcvd := make([]byte, 3)
+	n, err := s.connection.Read(rcvd)
+	if err != nil || n != 3 {
+		return 0, fmt.Errorf("n=%d not 3, or err = %v", n, err)
+	}
+	return uint16(rcvd[1])<<8 + uint16(rcvd[2]), nil
+
+}