dht

README

DHTxx temperature and humidity sensors

DHT11 ([pdf reference](https://raw.github.com/d2r2/go-dht/master/docs/DHT11 (1).pdf)) and DHT22 (pdf reference) sensors are quite popular among Arduino, Raspberry PI and their counterparts developers (here you will find comparision DHT11 vs DHT22):

They are cheap enough and affordable. So, here is a code written in Go programming language for Raspberry PI and counterparts, which gives you at the output temperature and humidity values (making all necessary signal processing via their own 1-wire bus protocol behind the scene).

Compatibility

Tested on Raspberry PI 1 (model B) and Banana PI (model M1).

Golang usage

func main() {
	// Read DHT11 sensor data from pin 4, retrying 10 times in case of failure.
	// You may enable "boost GPIO performance" parameter, if your device is old
	// as Raspberry PI 1 (this will require root privileges). You can switch off
	// "boost GPIO performance" parameter for old devices, but it may increase
	// retry attempts. Play with this parameter.
	temperature, humidity, retried, err :=
		dht.ReadDHTxxWithRetry(dht.DHT11, 4, true, 10)
	if err != nil {
		log.Fatal(err)
	}
	// Print temperature and humidity
	fmt.Printf("Temperature = %v*C, Humidity = %v%% (retried %d times)\n",
		temperature, humidity, retried)
}

Getting help

GoDoc documentation.

For detailed explanation read great article "Golang with Raspberry Pi : Read RH and Temperature from DHT22 or AM2302" written by Joseph Mathew. Thanks Joseph!

Installation

$ go get -u github.com/d2r2/go-dht

Quick tutorial

There are two functions you could use: ReadDHTxx(...) and ReadDHTxxWithRetry(...). They both do exactly same thing - activate sensor then read and decode temperature and humidity values. The only thing which distinguish one from another - "retry count" parameter as additinal argument in ReadDHTxxWithRetry(...). So, it's highly recomended to utilize ReadDHTxxWithRetry(...) with "retry count" not less than 7, since sensor asynchronouse protocol is not very stable causing errors time to time. Each additinal retry attempt takes 1.5-2 seconds (according to specification before repeated attempt you should wait 1-2 seconds).

This functionality works not only with Raspberry PI, but with counterparts as well (tested with Raspberry PI and Banana PI).

Note: If you enable "boost GPIO performance" parameter, application should run with root privileges, since C code inside requires this. In most cases it is sufficient to add "sudo -E" before "go run ...".

Note: This package does not require any external C code or library.

License

Go-dht is licensed under MIT License.

Documentation

Index

• func ReadDHTxx(sensorType SensorType, pin int, boostPerfFlag bool) (temperature float32, humidity float32, err error)
• func ReadDHTxxWithRetry(sensorType SensorType, pin int, boostPerfFlag bool, retry int) (temperature float32, humidity float32, retried int, err error)
• type Pulse
• type SensorType
  • func (this SensorType) String() string

Functions

func ReadDHTxx

func ReadDHTxx(sensorType SensorType, pin int,
	boostPerfFlag bool) (temperature float32, humidity float32, err error)

Send activation request to DHTxx sensor via specific pin. Then decode pulses sent back with asynchronous protocol specific for DHTxx sensors.

Input parameters: 1) sensor type: DHT11, DHT22 (aka AM2302); 2) pin number from GPIO connector to interract with sensor; 3) boost GPIO performance flag should be used for old devices such as Raspberry PI 1 (this will require root privileges).

Return: 1) temperature in Celsius; 2) humidity in percent; 3) error if present.

func ReadDHTxxWithRetry

func ReadDHTxxWithRetry(sensorType SensorType, pin int, boostPerfFlag bool,
	retry int) (temperature float32, humidity float32, retried int, err error)

Send activation request to DHTxx sensor via specific pin. Then decode pulses sent back with asynchronous protocol specific for DHTxx sensors. Retry n times in case of failure.

Input parameters: 1) sensor type: DHT11, DHT22 (aka AM2302); 2) pin number from gadget GPIO to interract with sensor; 3) boost GPIO performance flag should be used for old devices such as Raspberry PI 1 (this will require root privileges); 4) how many times to retry until success either сounter is zeroed.

Return: 1) temperature in Celsius; 2) humidity in percent; 3) number of extra retries data from sensor; 4) error if present.

Types

type Pulse

type Pulse struct {
	Value    byte
	Duration time.Duration
}

Keep pulse state with how long it lasted.

type SensorType

type SensorType int

const (
	// Most populare sensor
	DHT11 SensorType = iota + 1
	// More expensive and precise than DHT11
	DHT22
	// Aka DHT22
	AM2302 = DHT22
)

func (SensorType) String

func (this SensorType) String() string

Implement Stringer interface.