DHT22 Class Reference

An interrupt-driven library for the DHT22 sensor. More...

#include <DHT22.h>

Public Types
enum	Result {   None, Ok, ChecksumMismatch, WakeUpError,   DataError }
	Possible result values. More...
enum	Status { WakingUp, Reading, Done, Invalid }
	The status of the library state machine. More...

Public Member Functions
	DHT22 (int pin)
	Construct a DHT22 library instance. More...
void	onFallingEdge ()
	Signals the library that the data pin has gone low. More...
bool	startRead ()
	Wakes up the sensor and starts waiting for data. More...
Result	blockingRead ()
	Starts reading, if necessary, and waits for result. More...
int16_t	getTemp ()
	The last temperature reading. More...
uint16_t	getHumidity ()
	The last humidity reading. More...
Status	state ()
	The sensor status. More...
Result	lastResult ()
	The result of the last reading. More...

Detailed Description

An interrupt-driven library for the DHT22 sensor.

This class provides an interrupt-driven interface to the DHT22 sensor. The user must attach an ISR to the falling edge of the DHT22 data pin and invoke onFallingEdge() in the ISR.

Reading can be started with startRead(), which returns immediately, or blockingRead(), which waits for the reading to complete.

If state() returns Done, the data has been read and can be accessed with getTemp() and getHumidity(). Be aware of the measuring units!! If state() returns Invalid, lastResult() can give some information on the cause.

Usage example:

DHT22 dht(2);

void dhtISR() {
   dht.onFallingEdge();
}

void setup() {
    Serial.begin(9600);
    // On Arduino Uno, interrupt 0 is attached to pin 2
    attachInterrupt(0, &dhtISR, FALLING);
    // let the sensor warm up for 2 seconds
    delay(2000);
}

void loop() {
    if (dht.blockingRead() == DHT22::Ok) {
        Serial.print("Temperature: ");
        Serial.print(dht.getTemp()/10.0);
        Serial.println("C");
        Serial.print("Humidity: ");
        Serial.print(dht.getHumidity()/10.0);
        Serial.println("%");
    }
    // Minimum interval between reads.
    delay(2000);
}

Member Enumeration Documentation

enum DHT22::Result

Possible result values.

Enumerator
None	Data has never been read.
Ok	Yay!!
ChecksumMismatch	The data reading was currupted.
WakeUpError	There was a protocol timing error during the sensor wake-up.
DataError	There was a protocol timing error during data transmission.

enum DHT22::Status

The status of the library state machine.

Enumerator
WakingUp	The sensor is waking up.
Reading	The sensor is transmitting data.
Done	Data was successfully read.
Invalid	Data reading failed or was never attempted.

Constructor & Destructor Documentation

DHT22::DHT22

(

int

pin

)

Construct a DHT22 library instance.

Parameters

pin	The data pin of the sensor

Member Function Documentation

DHT22::Result DHT22::blockingRead

(

)

Starts reading, if necessary, and waits for result.

Returns

The reading result

uint16_t DHT22::getHumidity

(

)

The last humidity reading.

Returns

The relative humidity in per mil

int16_t DHT22::getTemp

(

)

The last temperature reading.

Returns

The temperature in tents of Celsius degree

DHT22::Result DHT22::lastResult

(

)

The result of the last reading.

void DHT22::onFallingEdge

(

)

Signals the library that the data pin has gone low.

bool DHT22::startRead

(

)

Wakes up the sensor and starts waiting for data.

Returns

Whether the reading was started

DHT22::Status DHT22::state

(

)

The sensor status.

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The documentation for this class was generated from the following files:

• DHT22.h
• DHT22.cpp