DHT22: add dht22 support

CONTRIBUTORS

@@ -40,4 +40,5 @@ Benoit Pereira da Silva <benoit.pereiradasilva@gmail.com>
 Stephan Sperber <sperberstephan@googlemail.com>
 Thorsten von Eicken <tve@voneicken.com>
 Weston Schmidt <weston_schmidt@alumni.purdue.edu>
+Voroshilin Andrey <voroshilin.andrey.08@gmail.com>
 

dht22/dht22.go

@@ -0,0 +1,161 @@
+// Package dht22 reads temperature and humidity from DHT22/AM2302 sensors.
+//
+// Datasheet: https://www.adafruit.com/datasheets/DHT22.pdf
+package dht22
+
+import (
+	"errors"
+	"sync"
+	"time"
+
+	"periph.io/x/conn/v3"
+	"periph.io/x/conn/v3/gpio"
+	"periph.io/x/conn/v3/physic"
+	"periph.io/x/conn/v3/pin"
+)
+
+// Dev represents a DHT22/AM2302 sensor.
+type Dev struct {
+    pin gpio.PinIO
+    mu  sync.Mutex
+}
+
+// New opens a connection to a DHT22 sensor on the given GPIO pin.
+func New(p gpio.PinIO) (*Dev, error) {
+    if err := p.In(gpio.PullUp, gpio.FallingEdge); err != nil {
+        return nil, err
+    }
+    return &Dev{pin: p}, nil
+}
+
+// SenseContinuous returns a channel that will receive measurements at the
+// specified interval. The channel is closed when stop is closed.
+func (d *Dev) SenseContinuous(interval time.Duration, stop <-chan struct{}) (<-chan physic.Env, error) {
+    ch := make(chan physic.Env)
+    go func() {
+        defer close(ch)
+        ticker := time.NewTicker(interval)
+        defer ticker.Stop()
+        for {
+            select {
+            case <-stop:
+                return
+            case <-ticker.C:
+                if env, err := d.Read(); err == nil {
+                    select {
+                    case ch <- env:
+                    case <-stop:
+                        return
+                    }
+                }
+            }
+        }
+    }()
+    return ch, nil
+}
+
+// Read reads temperature and humidity from the sensor.
+// Reading more frequently than once per 2 seconds may cause errors.
+func (d *Dev) Read() (physic.Env, error) {
+    d.mu.Lock()
+    defer d.mu.Unlock()
+
+    // Prepare pin for output
+    if err := d.pin.Out(gpio.Low); err != nil {
+        return physic.Env{}, err
+    }
+
+    // Send start signal: pull low for 1-10ms, then pull high for 20-40µs
+    d.pin.Out(gpio.Low)
+    time.Sleep(2 * time.Millisecond)
+    d.pin.Out(gpio.High)
+    time.Sleep(40 * time.Microsecond)
+
+    // Switch to input with pull-up
+    if err := d.pin.In(gpio.PullUp, gpio.NoEdge); err != nil {
+        return physic.Env{}, err
+    }
+
+    // Wait for sensor response
+    if !waitForState(d.pin, false, 80*time.Microsecond) {
+        return physic.Env{}, errors.New("dht22: no response from sensor")
+    }
+    if !waitForState(d.pin, true, 80*time.Microsecond) {
+        return physic.Env{}, errors.New("dht22: response timeout")
+    }
+
+    // Read 40 bits of data (humidity, temperature, checksum)
+    var data [5]byte
+    for i := 0; i < 40; i++ {
+        if !waitForState(d.pin, false, 50*time.Microsecond) {
+            return physic.Env{}, errors.New("dht22: data sync error")
+        }
+
+        // High pulse length determines bit value
+        start := time.Now()
+        waitForState(d.pin, true, 70*time.Microsecond)
+        duration := time.Since(start)
+
+        bit := byte(i / 8)
+        shift := 7 - (i % 8)
+        if duration > 50*time.Microsecond {
+            data[bit] |= 1 << shift
+        }
+    }
+
+    // Verify checksum
+    checksum := data[0] + data[1] + data[2] + data[3]
+    if data[4] != checksum {
+        return physic.Env{}, errors.New("dht22: checksum error")
+    }
+
+    // Parse data (big-endian)
+    humidityInt := uint16(data[0])<<8 | uint16(data[1])
+    tempRaw := int16(uint16(data[2])<<8 | uint16(data[3]))
+
+    // Convert to physic units
+    // humidity is 0.1% RH units, so divide by 10 to get percent
+    humidity := physic.RelativeHumidity(float64(humidityInt)/10.0) * physic.PercentRH
+
+    // temperature is 0.1°C units, with bit 15 for sign
+    // Convert to nano Kelvin (base unit for physic.Temperature)
+    // 1°C = 1K in delta, but physic uses nanoKelvin
+    temperature := physic.Temperature(float64(tempRaw)/10.0) * physic.Celsius
+
+    env := physic.Env{
+        Humidity:    humidity,
+        Temperature: temperature,
+    }
+
+    return env, nil
+}
+
+// String implements conn.Resource.
+func (d *Dev) String() string {
+    return "DHT22{" + d.pin.String() + "}"
+}
+
+// Halt implements conn.Resource.
+func (d *Dev) Halt() error {
+    return d.pin.Halt()
+}
+
+// Pin returns the GPIO pin used by the sensor.
+func (d *Dev) Pin() pin.Pin {
+    return d.pin
+}
+
+// waitForState waits for pin to reach desired state within timeout.
+func waitForState(p gpio.PinIO, state bool, timeout time.Duration) bool {
+    deadline := time.Now().Add(timeout)
+    for time.Now().Before(deadline) {
+        if p.Read() == gpio.Level(state) {
+            return true
+        }
+        time.Sleep(1 * time.Microsecond)
+    }
+    return false
+}
+
+// Ensure Dev implements conn.Resource.
+var _ conn.Resource = &Dev{}