DHT22Gen3 Class Reference

Class for interfacing with one or more DHT22 sensors on a Gen3 Particle device. More...

#include <DHT22Gen3_RK.h>

Public Types
enum	State { State::IDLE_STATE, State::START_STATE, State::SEND_START_STATE, State::SAMPLING_STATE }
	Enumeration for possible states for the Finite State Machine. More...

Public Member Functions
	DHT22Gen3 (pin_t unusedPin1, pin_t unusedPin2)
	Initialize the DHT22Gen3 driver. More...
void	setup ()
	Call from setup() to initialize the driver.
void	loop ()
	Call from loop(), preferably every call to loop. More...
void	getSample (pin_t dhtPin, std::function< void(DHTSample)> completion, DHTSensorType *sensorType=&sensorTypeDHT22)
	Get a sample on the specified pin. More...
bool	canGetSample () const
	Returns true if you can call getSample(). Returns false if another call is still in progress.
DHTSample	getLastResult () const
	Gets the last result if you want to poll instead of use the completion function.
DHT22Gen3 &	withMaxTries (int tries)
	Maximum number of attempts to get a valid result (passes checksum). Default is 4. More...

Static Public Attributes
static DHTSensorTypeDHT11	sensorTypeDHT11
	Pass a pointer to sensorTypeDHT11 to getSamples() for DHT11 sensors.
static DHTSensorTypeDHT22	sensorTypeDHT22
	Pass a pointer to sensorTypeDHT22 to getSamples() for DHT22 sensors. This is the default.

Protected Member Functions
void	callCompletion (DHTSample::SampleResult sampleResult)
	Used internally to call the completion handler. More...

Protected Attributes
pin_t	unusedPin1
	Pin to output SCK (not used by DHT22, but unfortunately required by I2S)
pin_t	unusedPin2
	Pin to output LRCK (not used by DHT22, but unfortunately required by I2S)
pin_t	dhtPin = 0
	Pin to communicate with DHT22. Set by getSample()
DHTSensorType *	sensorType = &sensorTypeDHT22
	Sensor type, optional parameter to getSample();.
unsigned long	lastRequestTime = 0
	millis() value at last request. Used to prevent querying more often than minSamplePeriodMs (2 seconds)
unsigned long	stateTime = 0
	millis() value used with state transitions
int	maxTries = 4
	Maximum number of retries on checksum values. Default is 4. Each retry takes 2.5 seconds.
State	state = State::IDLE_STATE
	State of the finite state machine.
DHTSample	result
	Result that will be passed to the callback (by value)
std::function< void(DHTSample)>	completion = 0
	Completion handler function or lambda. Set by getSample(). May be 0.

Detailed Description

Class for interfacing with one or more DHT22 sensors on a Gen3 Particle device.

Only allocate one of these, typically as a global variable, per device.

Be sure to call the setup() and loop() methods from the actual setup and loop.

Member Enumeration Documentation

State

enum DHT22Gen3::State

strong

Enumeration for possible states for the Finite State Machine.

Enumerator
IDLE_STATE	Idle, can call getSample()
START_STATE	Getting ready to get a sample.
SEND_START_STATE	Sending the start bit and starting the I2S peripheral.
SAMPLING_STATE	Capturing samples.

Constructor & Destructor Documentation

DHT22Gen3()

DHT22Gen3::DHT22Gen3	(	pin_t	unusedPin1,
		pin_t	unusedPin2
	)

Initialize the DHT22Gen3 driver.

Parameters

unusedPin1	An unused GPIO pin to use for SCK. It's unfortunate, but for the I2S peripheral to work, SCK must be mapped to a valid pin. It will be set to output and there will be 512 KHz signal output on this pin.
unusedPin2	An unused GPIO pin to use for LRCK. It's unfortunate, but for the I2S peripheral to work, LRCK must be mapped to a valid pin. It will be set to output and there will be 32 KHz signal output on this pin. It must be a different pin than unusedPin1.

• You will often allocate this object as a global variable.
• There can only be one per device.
• Make sure you call setup() and loop() methods from your actual setup() and loop()!

Member Function Documentation

callCompletion()

void DHT22Gen3::callCompletion ( DHTSample::SampleResult  sampleResult )

protected

Used internally to call the completion handler.

Goes into IDLE state after calling the completion

getSample()

void DHT22Gen3::getSample	(	pin_t	dhtPin,
		std::function< void(DHTSample)>	completion,
		DHTSensorType *	sensorType = &sensorTypeDHT22
	)

Get a sample on the specified pin.

Parameters

dhtPin	The pin the sensor is connected to (A0, A1, ..., D0, D1, ...) can also use special pins when the port is not being use, for example, TX, RX, MISO, MOSI, SCK.
completion	A function or C++ lambda to call when the operation completes.
sensorType	Optional. Default to &sensorTypeDHT22. Can also be &sensorTypeDHT11.

This function is asynchronous and the completion function is called when done.

Normal operation takes 24 milliseconds. If a checksum failure occurs, each retry takes 2 seconds because the DHT22 cannot get new samples faster than that. So with 4 retries, it could take about 9 seconds.

loop()

void DHT22Gen3::loop

(

)

Call from loop(), preferably every call to loop.

This allows the completion function to be dispatched from normal loop execution time, which allows normal calls like Particle.publish to be called safely.

withMaxTries()

DHT22Gen3& DHT22Gen3::withMaxTries ( int  tries )

inline

Maximum number of attempts to get a valid result (passes checksum). Default is 4.

Note that each retry takes 2.25 seconds, so you may not want to set the value too high.

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

• src/DHT22Gen3_RK.h
• src/DHT22Gen3_RK.cpp