├── readme.md
└── dht22.go


/readme.md:
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 1 | Greetings do it yourselfers!
 2 | 
 3 | It's AM2302/DHT22 library. No external c libraries. 
 4 | 
 5 | ## installation 
 6 | `go get github.com/morus12/dht22`
 7 | 
 8 | ## usage
 9 | ```
10 | import "github.com/morus12/dht22"
11 | 
12 | sensor := dht22.New("GPIO_17")
13 | temperature, err := sensor.Temperature()
14 | humidity, err := sensor.Humidity()
15 | ```
16 | 
17 | ## testing environmnet 
18 | - Raspberry Pi 3
19 | - two DHT22 sensors
20 | - go1.7.5 linux/arm
21 | - Raspbian GNU/Linux 8
22 | 
23 | Pi3 has 64 bit CPU, but system was setup on 32bit. Currently (Feb 2016) there is no official linux/arm64 kernel for Pi 3.


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/dht22.go:
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  1 | package dht22
  2 | 
  3 | import (
  4 | 	"errors"
  5 | 	"time"
  6 | 
  7 | 	"github.com/kidoman/embd"
  8 | 	_ "github.com/kidoman/embd/host/rpi"
  9 | )
 10 | 
 11 | // AM2302/DHT22 - digital relative humidity and temperature sensor
 12 | // https://cdn-shop.adafruit.com/datasheets/Digital+humidity+and+temperature+sensor+AM2302.pdf
 13 | 
 14 | const (
 15 | 	COLLECTING_PERIOD  = 2 * time.Second
 16 | 	LOGICAL_1_TRESHOLD = 50 * time.Microsecond
 17 | )
 18 | 
 19 | var (
 20 | 	ChecksumError    = errors.New("checksum error")
 21 | 	HumidityError    = errors.New("humidity range error")
 22 | 	TemperatureError = errors.New("temperature range error")
 23 | )
 24 | 
 25 | type DHT22 struct {
 26 | 	pin         string
 27 | 	temperature float32
 28 | 	humidity    float32
 29 | 	readAt      time.Time
 30 | 	err         error
 31 | }
 32 | 
 33 | func New(pin string) *DHT22 {
 34 | 	return &DHT22{pin: pin}
 35 | }
 36 | 
 37 | func (d *DHT22) Temperature() (float32, error) {
 38 | 	if err := d.read(); err != nil {
 39 | 		d.err = err
 40 | 		return 0, err
 41 | 	}
 42 | 
 43 | 	return d.temperature, nil
 44 | }
 45 | 
 46 | func (d *DHT22) Humidity() (float32, error) {
 47 | 	if err := d.read(); err != nil {
 48 | 		d.err = err
 49 | 		return 0, err
 50 | 	}
 51 | 
 52 | 	return d.humidity, nil
 53 | }
 54 | 
 55 | func (d *DHT22) read() error {
 56 | 	if d.readAt.Add(COLLECTING_PERIOD).After(time.Now()) {
 57 | 		return d.err
 58 | 	}
 59 | 
 60 | 	d.err = nil
 61 | 
 62 | 	d.readAt = time.Now()
 63 | 
 64 | 	// early allocations before time critical code
 65 | 	lengths := make([]time.Duration, 40)
 66 | 	iterator := 0
 67 | 
 68 | 	embd.InitGPIO()
 69 | 	defer embd.CloseGPIO()
 70 | 
 71 | 	pin, err := embd.NewDigitalPin(d.pin)
 72 | 	if err != nil {
 73 | 		return err
 74 | 	}
 75 | 
 76 | 	defer pin.Close()
 77 | 
 78 | 	if err := pin.SetDirection(embd.Out); err != nil {
 79 | 		return err
 80 | 	}
 81 | 
 82 | 	if err := pin.Write(embd.High); err != nil {
 83 | 		return err
 84 | 	}
 85 | 
 86 | 	// send init values
 87 | 	time.Sleep(250 * time.Millisecond)
 88 | 	if err := pin.Write(embd.Low); err != nil {
 89 | 		return err
 90 | 	}
 91 | 
 92 | 	time.Sleep(5 * time.Millisecond)
 93 | 
 94 | 	if err := pin.Write(embd.High); err != nil {
 95 | 		return err
 96 | 	}
 97 | 
 98 | 	time.Sleep(20 * time.Microsecond)
 99 | 
100 | 	if err := pin.SetDirection(embd.In); err != nil {
101 | 		return err
102 | 	}
103 | 
104 | 	// read data
105 | 	for {
106 | 		duration, err := pin.TimePulse(embd.High)
107 | 		if err != nil {
108 | 			return err
109 | 		}
110 | 		lengths[iterator] = duration
111 | 		iterator++
112 | 		if iterator >= 40 {
113 | 			break
114 | 		}
115 | 	}
116 | 
117 | 	// convert to bytes
118 | 	bytes := make([]uint8, 5)
119 | 
120 | 	for i := range bytes {
121 | 		for j := 0; j < 8; j++ {
122 | 			bytes[i] <<= 1
123 | 			if lengths[i*8+j] > LOGICAL_1_TRESHOLD {
124 | 				bytes[i] |= 0x01
125 | 			}
126 | 		}
127 | 	}
128 | 
129 | 	if err := d.checksum(bytes); err != nil {
130 | 		if err != nil {
131 | 			return err
132 | 		}
133 | 	}
134 | 
135 | 	var (
136 | 		humidity    uint16
137 | 		temperature uint16
138 | 	)
139 | 
140 | 	// calculate humidity
141 | 
142 | 	humidity |= uint16(bytes[0])
143 | 	humidity <<= 8
144 | 	humidity |= uint16(bytes[1])
145 | 
146 | 	if humidity < 0 || humidity > 1000 {
147 | 		return HumidityError
148 | 	}
149 | 
150 | 	d.humidity = float32(humidity) / 10
151 | 
152 | 	// calculate temperature
153 | 	temperature |= uint16(bytes[2])
154 | 	temperature <<= 8
155 | 	temperature |= uint16(bytes[3])
156 | 
157 | 	// check for negative temperature
158 | 	if temperature&0x8000 > 0 {
159 | 		d.temperature = float32(temperature&0x7FFF) / -10
160 | 	} else {
161 | 		d.temperature = float32(temperature) / 10
162 | 	}
163 | 
164 | 	// datasheet operating range
165 | 	if d.temperature < -40 || d.temperature > 80 {
166 | 		return TemperatureError
167 | 	}
168 | 
169 | 	return nil
170 | }
171 | 
172 | func (d *DHT22) checksum(bytes []uint8) error {
173 | 	var sum uint8
174 | 
175 | 	for i := 0; i < 4; i++ {
176 | 		sum += bytes[i]
177 | 	}
178 | 
179 | 	if sum != bytes[4] {
180 | 		return ChecksumError
181 | 	}
182 | 
183 | 	return nil
184 | }
185 | 


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