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|
package dht11
import (
"errors"
"log"
"time"
"github.com/stianeikeland/go-rpio"
)
type tempState int
const (
initPullDown tempState = iota
initPullUp
dataFirstPullDown
dataPullUp
dataPullDown
)
type SensorData struct {
TempC int
TempF float32
Humidity int
}
type Device struct {
StartLowTime time.Duration
LowTime time.Duration
HighTime time.Duration
ReadDelay time.Duration
}
var RaspberryPi Device
func init() {
// These were determined experimentally using a logic analyser a Raspberry
// Pi 3 B+. They may vary for other device types and processor speeds.
RaspberryPi = Device{
StartLowTime: 4 * time.Microsecond,
LowTime: 15 * time.Millisecond,
HighTime: 50 * time.Millisecond,
ReadDelay: 1 * time.Microsecond,
}
}
type DHT11 struct {
Device *Device
Pin *rpio.Pin
}
func NewRaspberryPiDHT11(pin *rpio.Pin) *DHT11 {
return &DHT11{
Device: &RaspberryPi,
Pin: pin,
}
}
func (d *DHT11) sendDataRequest() {
d.Pin.Output()
d.Pin.Low()
time.Sleep(d.Device.StartLowTime)
d.Pin.High()
time.Sleep(d.Device.HighTime)
d.Pin.Low()
time.Sleep(d.Device.LowTime)
d.Pin.Input()
d.Pin.PullUp()
}
func (d *DHT11) gatherRawData() []rpio.State {
var i int
var last rpio.State
data := make([]rpio.State, 0)
for i = 0; i < 500; i++ {
current := d.Pin.Read()
time.Sleep(d.Device.ReadDelay)
data = append(data, current)
if last != current {
i = 0
last = current
}
}
return data
}
func (d *DHT11) parseSignals(input []rpio.State) ([]int, error) {
state := initPullDown
lengths := make([]int, 0, 40)
currentLength := 0
for _, current := range input {
currentLength++
switch state {
case initPullDown:
if current == rpio.Low {
state = initPullUp
}
case initPullUp:
if current == rpio.High {
state = dataFirstPullDown
}
case dataFirstPullDown:
if current == rpio.Low {
state = dataPullUp
}
case dataPullUp:
if current == rpio.High {
currentLength = 0
state = dataPullDown
}
case dataPullDown:
if current == rpio.Low {
lengths = append(lengths, currentLength)
state = dataPullUp
}
}
}
if len(lengths) != 40 {
return nil, errors.New("not enough data returned")
}
return lengths, nil
}
func (d *DHT11) signalsToBytes(lengths []int) ([]int, error) {
bytes := make([]int, 0, 5)
longestUp, shortestUp := 0, 1000
for _, length := range lengths {
if length < shortestUp {
shortestUp = length
}
if length > longestUp {
longestUp = length
}
}
halfway := shortestUp + (longestUp-shortestUp)/2
bits := make([]bool, 0, len(lengths))
for _, length := range lengths {
bit := false
if length > halfway {
bit = true
}
bits = append(bits, bit)
}
currentByte := 0
for i, bit := range bits {
currentByte <<= 1
if bit {
currentByte |= 1
} else {
currentByte |= 0
}
if (i+1)%8 == 0 {
bytes = append(bytes, currentByte)
currentByte = 0
}
}
checksum := (bytes[0] + bytes[1] + bytes[2] + bytes[3]) & 255
if bytes[4] != checksum {
return nil, errors.New("CRC error")
}
return bytes, nil
}
func (d *DHT11) GetSensorData() (*SensorData, error) {
d.sendDataRequest()
rawData := d.gatherRawData()
signals, err := d.parseSignals(rawData)
if err != nil {
return nil, err
}
dataBytes, err := d.signalsToBytes(signals)
if err != nil {
return nil, err
}
return &SensorData{
TempC: dataBytes[2],
TempF: celsiusToFarenheit(dataBytes[2]),
Humidity: dataBytes[0],
}, nil
}
func (d *DHT11) GetSensorDataWithRetry(rc int) (data *SensorData, err error) {
for i := 0; i < rc; i++ {
data, err = d.GetSensorData()
if err == nil {
return
} else {
log.Printf("error")
time.Sleep(1 * time.Second)
continue
}
}
return
}
func celsiusToFarenheit(c int) float32 {
return float32(c)*1.8 + 32
}
|
