Merge pull request hybridgroup#352 from schmidtw/dev

Add a driver for the sht3x chip.

Makefile

@@ -51,3 +51,4 @@ deps:
 	go get -d -v github.com/lazywei/go-opencv
 	go get -d -v github.com/donovanhide/eventsource
 	go get -d -v github.com/hashicorp/go-multierror
+	go get -d -v github.com/sigurn/crc8

README.md

@@ -258,6 +258,7 @@ drivers provided using the `gobot/drivers/i2c` package:
 	- MMA7660 3-Axis Accelerometer
 	- MPL115A2 Barometer
 	- MPU6050 Accelerometer/Gyroscope
+	- SHT3x-D Temperature/Humidity
 	- Wii Nunchuck Controller
 
 More platforms and drivers are coming soon...

drivers/i2c/README.md

@@ -25,6 +25,7 @@ Gobot has a extensible system for connecting to hardware devices. The following
 - MMA7660 3-Axis Accelerometer
 - MPL115A2 Barometer
 - MPU6050 Accelerometer/Gyroscope
+- SHT3x-D Temperature/Humidity
 - Wii Nunchuck Controller
 
 More drivers are coming soon...

drivers/i2c/sht3x_driver.go

@@ -0,0 +1,218 @@
+/*
+ * 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
+
+// SHT3xDriver is a driver for the SHT3x-D based devices.
+//
+// This module was tested with AdaFruit Sensiron SHT32-D Breakout.
+// https://www.adafruit.com/products/2857
+
+import (
+	"errors"
+	"github.com/sigurn/crc8"
+	"gobot.io/x/gobot"
+	"time"
+)
+
+// SHT3xAddressA is the default address of device
+const SHT3xAddressA = 0x44
+
+// SHT3xAddressB is the optional address of device
+const SHT3xAddressB = 0x45
+
+// SHT3xAccuracyLow is the faster, but lower accuracy sample setting
+const SHT3xAccuracyLow = 0x16
+
+// SHT3xAccuracyMedium is the medium accuracy and speed sample setting
+const SHT3xAccuracyMedium = 0x0b
+
+// SHT3xAccuracyHigh is the high accuracy and slowest sample setting
+const SHT3xAccuracyHigh = 0x00
+
+var (
+	crc8Params         = crc8.Params{0x31, 0xff, false, false, 0x00, 0xf7, "CRC-8/SENSIRON"}
+	ErrInvalidAccuracy = errors.New("Invalid accuracy")
+	ErrInvalidCrc      = errors.New("Invalid crc")
+	ErrInvalidTemp     = errors.New("Invalid temperature units")
+)
+
+// SHT3xDriver is a Driver for a SHT3x humidity and temperature sensor
+type SHT3xDriver struct {
+	Units string
+
+	name         string
+	connection   I2c
+	sht3xAddress int
+	accuracy     byte
+	delay        time.Duration
+	crcTable     *crc8.Table
+}
+
+// NewSHT3xDriver creates a new driver with specified i2c interface
+func NewSHT3xDriver(a I2c) *SHT3xDriver {
+	s := &SHT3xDriver{
+		Units:        "C",
+		name:         "SHT3x",
+		connection:   a,
+		sht3xAddress: SHT3xAddressA,
+		crcTable:     crc8.MakeTable(crc8Params),
+	}
+	s.SetAccuracy(SHT3xAccuracyHigh)
+	return s
+}
+
+// Name returns the name for this Driver
+func (s *SHT3xDriver) Name() string { return s.name }
+
+// SetName sets the name for this Driver
+func (s *SHT3xDriver) SetName(n string) { s.name = n }
+
+// Connection returns the connection for this Driver
+func (s *SHT3xDriver) Connection() gobot.Connection { return s.connection.(gobot.Connection) }
+
+// Start initializes the SHT3x
+func (s *SHT3xDriver) Start() (err error) {
+	err = s.connection.I2cStart(s.sht3xAddress)
+	return
+}
+
+// Halt returns true if devices is halted successfully
+func (s *SHT3xDriver) Halt() (err error) { return }
+
+// SetAddress sets the address of the device
+func (s *SHT3xDriver) SetAddress(address int) { s.sht3xAddress = address }
+
+// Accuracy returns the accuracy of the sampling
+func (s *SHT3xDriver) Accuracy() byte { return s.accuracy }
+
+// SetAccuracy sets the accuracy of the sampling
+func (s *SHT3xDriver) SetAccuracy(a byte) (err error) {
+	switch a {
+	case SHT3xAccuracyLow:
+		s.delay = 5 * time.Millisecond // Actual max is 4, wait 1 ms longer
+	case SHT3xAccuracyMedium:
+		s.delay = 7 * time.Millisecond // Actual max is 6, wait 1 ms longer
+	case SHT3xAccuracyHigh:
+		s.delay = 16 * time.Millisecond // Actual max is 15, wait 1 ms longer
+	default:
+		err = ErrInvalidAccuracy
+		return
+	}
+
+	s.accuracy = a
+
+	return
+}
+
+// SerialNumber returns the serial number of the chip
+func (s *SHT3xDriver) SerialNumber() (sn uint32, err error) {
+	ret, err := s.sendCommandDelayGetResponse([]byte{0x37, 0x80}, nil, 2)
+	if nil == err {
+		sn = (uint32(ret[0]) << 16) | uint32(ret[1])
+	}
+
+	return
+}
+
+// Heater returns true if the heater is enabled
+func (s *SHT3xDriver) Heater() (status bool, err error) {
+	sr, err := s.getStatusRegister()
+	if err == nil {
+		if (1 << 13) == (sr & (1 << 13)) {
+			status = true
+		}
+	}
+	return
+}
+
+// SetHeater enables or disables the heater on the device
+func (s *SHT3xDriver) SetHeater(enabled bool) (err error) {
+	out := []byte{0x30, 0x66}
+	if true == enabled {
+		out[1] = 0x6d
+	}
+	return s.connection.I2cWrite(s.sht3xAddress, out)
+}
+
+// Sample returns the temperature in celsius and relative humidity for one sample
+func (s *SHT3xDriver) Sample() (temp float32, rh float32, err error) {
+	ret, err := s.sendCommandDelayGetResponse([]byte{0x24, s.accuracy}, &s.delay, 2)
+	if nil != err {
+		return
+	}
+
+	// From the datasheet:
+	// RH = 100 * Srh / (2^16 - 1)
+	rhSample := uint64(ret[1])
+	rh = float32((uint64(1000000)*rhSample)/uint64(0xffff)) / 10000.0
+
+	tempSample := uint64(ret[0])
+	switch s.Units {
+	case "C":
+		// From the datasheet:
+		// T[C] = -45 + 175 * (St / (2^16 - 1))
+		temp = float32((uint64(1750000)*tempSample)/uint64(0xffff)-uint64(450000)) / 10000.0
+	case "F":
+		// From the datasheet:
+		// T[F] = -49 + 315 * (St / (2^16 - 1))
+		temp = float32((uint64(3150000)*tempSample)/uint64(0xffff)-uint64(490000)) / 10000.0
+	default:
+		err = ErrInvalidTemp
+	}
+
+	return
+}
+
+// getStatusRegister returns the device status register
+func (s *SHT3xDriver) getStatusRegister() (status uint16, err error) {
+	ret, err := s.sendCommandDelayGetResponse([]byte{0xf3, 0x2d}, nil, 1)
+	if nil == err {
+		status = ret[0]
+	}
+	return
+}
+
+// sendCommandDelayGetResponse is a helper function to reduce duplicated code
+func (s *SHT3xDriver) sendCommandDelayGetResponse(send []byte, delay *time.Duration, expect int) (read []uint16, err error) {
+	if err = s.connection.I2cWrite(s.sht3xAddress, send); err != nil {
+		return
+	}
+
+	if nil != delay {
+		time.Sleep(*delay)
+	}
+
+	got, err := s.connection.I2cRead(s.sht3xAddress, 3*expect)
+	if err != nil {
+		return
+	}
+	if len(got) != (3 * expect) {
+		err = ErrNotEnoughBytes
+		return
+	}
+
+	read = make([]uint16, expect)
+	for i := 0; i < expect; i++ {
+		crc := crc8.Checksum(got[i*3:i*3+2], s.crcTable)
+		if got[i*3+2] != crc {
+			err = ErrInvalidCrc
+			return
+		}
+		read[i] = uint16(got[i*3])<<8 | uint16(got[i*3+1])
+	}
+
+	return
+}