garyns/pigpio-dht

DHT11 Temperature and Humidity Sensor using pigpio

pigpio-dht

DHT11 and DHT22 Driver Library based on the pigpio GPIO library.

Installation

pip install pigpio-dht

Supported Versions of Python

Tested against Python >= 3.5.

May work with earlier 3.X versions but this has not been confirmed. Does not work with Python 2.7.

Links

• GitHub Repository

DHT Sensors are Slow

DHT sensors are slow to take readings, and need to settle between reads. For instance, the maximum read rates for the sensors are:

• DHT11 once every 1 seconds
• DHT22 once every 2 seconds

This library monitors the read rate and will pause between successive calls to read() to honor these limits.

Examples

One-Shot Read

Take a single reading from the sensor.

Code

# NOTE: The import has a _ not - in the module name.
from pigpio_dht import DHT11, DHT22

gpio = 21 # BCM Numbering

sensor = DHT11(gpio)
#sensor = DHT22(gpio)

result = sensor.read()
print(result)

Output

{'temp_c': 20, 'temp_f': 68.0, 'humidity': 35, 'valid': True}

Also see

read()

Sampled Read

Take many readings (by repeating calling read()) from the sensor and return a normalised result.

Code

# NOTE: The import has a _ not - in the module name.
from pigpio_dht import DHT11, DHT22

gpio = 21 # BCM Numbering

sensor = DHT11(gpio)
#sensor = DHT22(gpio)

result = sensor.sample(samples=5)
print(result)

Output

{'temp_c': 20, 'temp_f': 68.0, 'humidity': 35, 'valid': True}

Also see

sample()

API

The classes DHT11 and DHT22 both extend the base class DHTXX and share a common API.

Constructor: DHT11 | DHT22(gpio, timeout_secs=0.5, use_internal_pullup=True, pi=None)

Parameters

• gpio GPIO (BCM) pin that data leg of sensor is connected to
• timeout_secs Sensor timeout in second. Default should be adequate unless you receive a TimeoutError advising you to increase the value wuth calling read() or sample()
• use_internal_pullup - Enable internal pull-up resistor on gpio
• pi a custom instance of pigpio.pi()

read(retries=0) raises TimeoutError

Take a single reading from the sensor.

Parameters

• retries number of times to keep retrying when the result contains valid = False

Returns

A Dictionary in the form {'temp_c': 20, 'temp_f': 68.0, 'humidity': 35, 'valid': True}

Where:

• temp_c is the temperature in degrees Celsius
• temp_f is the temperature in degrees Fahrenheit
• humidity is the relative humidity
• valid is true only if sensors checksum matches with returned data.

Discard readings where value == False and try again.

Raises

TimeoutError

• If the sensor on gpio does not respond
• If the sensor responds within timeout_secs (see _Constructor), but the response cannot be understood by the library. Try increasing timeout_secs

Also see

DHT Sensors are Slow

sample(samples=5, max_retries=None) raises TimeoutError

Take many readings (by repeating calling read()) from the sensor and return a normalised result.

Please note that a call to sample() takes time. For example for the DHT11 with a maximum read rate of once every 1 seconds, 5 samples will take approximately 1 second * 5 samples = 5 seconds.

Parameters:

• samples number of samples to take
• max_retries maximum number of times to keep retrying per sample when the result contains valid = False. Default to samples * 2

Raises

TimeoutError

• Same as for read(), plus
• If max_retries is reached