DHTXX driver (#235)

dhtXX: add new driver for dht thermometer

dht/constants.go

@@ -0,0 +1,116 @@
+// Package dht provides a driver for DHTXX family temperature and humidity sensors.
+//
+// [1] Datasheet DHT11: https://www.mouser.com/datasheet/2/758/DHT11-Technical-Data-Sheet-Translated-Version-1143054.pdf
+// [2] Datasheet DHT22: https://cdn-shop.adafruit.com/datasheets/Digital+humidity+and+temperature+sensor+AM2302.pdf
+// Adafruit C++ driver: https://github.com/adafruit/DHT-sensor-library
+
+package dht // import "tinygo.org/x/drivers/dht"
+
+import (
+	"encoding/binary"
+	"machine"
+	"time"
+)
+
+// enum type for device type
+type DeviceType uint8
+
+// DeviceType specific parsing of information received from the sensor
+func (d DeviceType) extractData(buf []byte) (temp int16, hum uint16) {
+	if d == DHT11 {
+		temp = int16(buf[2])
+		if buf[3]&0x80 > 0 {
+			temp = -1 - temp
+		}
+		temp *= 10
+		temp += int16(buf[3] & 0x0f)
+		hum = 10*uint16(buf[0]) + uint16(buf[1])
+	} else {
+		hum = binary.LittleEndian.Uint16(buf[0:2])
+		temp = int16(buf[3])<<8 + int16(buf[2]&0x7f)
+		if buf[2]&0x80 > 0 {
+			temp = -temp
+		}
+	}
+	return
+}
+
+// Celsius and Fahrenheit temperature scales
+type TemperatureScale uint8
+
+func (t TemperatureScale) convertToFloat(temp int16) float32 {
+	if t == C {
+		return float32(temp) / 10
+	} else {
+		// Fahrenheit
+		return float32(temp)*(9.0/50.) + 32.
+	}
+}
+
+// All functions return ErrorCode instance as error. This class can be used for more efficient error processing
+type ErrorCode uint8
+
+const (
+	startTimeout = time.Millisecond * 200
+	startingLow  = time.Millisecond * 20
+
+	DHT11 DeviceType = iota
+	DHT22
+
+	C TemperatureScale = iota
+	F
+
+	ChecksumError ErrorCode = iota
+	NoSignalError
+	NoDataError
+	UpdateError
+	UninitializedDataError
+)
+
+// error interface implementation for ErrorCode
+func (e ErrorCode) Error() string {
+	switch e {
+	case ChecksumError:
+		// DHT returns ChecksumError if all the data from the sensor was received, but the checksum does not match.
+		return "checksum mismatch"
+	case NoSignalError:
+		// DHT returns NoSignalError if there was no reply from the sensor. Check sensor connection or the correct pin
+		// sis chosen,
+		return "no signal"
+	case NoDataError:
+		// DHT returns NoDataError if the connection was successfully initialized, but not all 40 bits from
+		// the sensor is received
+		return "no data"
+	case UpdateError:
+		// DHT returns UpdateError if ReadMeasurements function is called before time specified in UpdatePolicy or
+		// less than 2 seconds after past measurement
+		return "cannot update now"
+	case UninitializedDataError:
+		// DHT returns UninitializedDataError if user attempts to access data before first measurement
+		return "no measurements done"
+	}
+	// should never be reached
+	return "unknown error"
+}
+
+// Update policy of the DHT device. UpdateTime cannot be shorter than 2 seconds. According to dht specification sensor
+// will return undefined data if update requested less than 2 seconds before last usage
+type UpdatePolicy struct {
+	UpdateTime          time.Duration
+	UpdateAutomatically bool
+}
+
+var (
+	// timeout counter equal to number of ticks per 1 millisecond
+	timeout counter
+)
+
+func init() {
+	timeout = cyclesPerMillisecond()
+}
+
+func cyclesPerMillisecond() counter {
+	freq := machine.CPUFrequency()
+	freq /= 1000
+	return counter(freq)
+}