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.. _2.2.3_py:
2.2.3 DHT-11
============
Introduction
--------------
In this lesson, you will learn how to connect and read data from a DHT11 temperature and humidity sensor using a Raspberry Pi. You will learn how to set up the sensor, read temperature in both Celsius and Fahrenheit, and obtain humidity readings. This project introduces you to working with external sensors, handling real-time data, and basic exception handling in Python.
Required Components
------------------------------
In this project, we need the following components.
.. image:: ../img/list_2.2.3_dht-11.png
It's definitely convenient to buy a whole kit, here's the link:
.. list-table::
:widths: 20 20 20
:header-rows: 1
* - Name
- ITEMS IN THIS KIT
- LINK
* - Raphael Kit
- 337
- |link_Raphael_kit|
You can also buy them separately from the links below.
.. list-table::
:widths: 30 20
:header-rows: 1
* - COMPONENT INTRODUCTION
- PURCHASE LINK
* - :ref:`cpn_gpio_board`
- |link_gpio_board_buy|
* - :ref:`cpn_breadboard`
- |link_breadboard_buy|
* - :ref:`cpn_wires`
- |link_wires_buy|
* - :ref:`cpn_resistor`
- |link_resistor_buy|
* - :ref:`cpn_humiture_sensor`
- |link_humiture_buy|
Schematic Diagram
-----------------
.. image:: ../img/image326.png
Experimental Procedures
-----------------------
**Step 1:** Build the circuit.
.. image:: ../img/image207.png
**Step 2:** Go to the folder of the code.
.. raw:: html
.. code-block::
cd ~/raphael-kit/python
**Step 3:** Run the executable file.
.. raw:: html
.. code-block::
sudo python3 2.2.3_DHT.py
After the code runs, the program will print the temperature and humidity
detected by DHT11 on the computer screen.
**Code**
.. note::
You can **Modify/Reset/Copy/Run/Stop** the code below. But before that, you need to go to source code path like ``raphael-kit/python``. After modifying the code, you can run it directly to see the effect.
.. code-block:: python
from gpiozero import OutputDevice, InputDevice
import time
class DHT11():
MAX_DELAY_COUINT = 100
BIT_1_DELAY_COUNT = 10
BITS_LEN = 40
def __init__(self, pin, pull_up=False):
self._pin = pin
self._pull_up = pull_up
def read_data(self):
bit_count = 0
delay_count = 0
bits = ""
# -------------- send start --------------
gpio = OutputDevice(self._pin)
gpio.off()
time.sleep(0.02)
gpio.close()
gpio = InputDevice(self._pin, pull_up=self._pull_up)
# -------------- wait response --------------
while gpio.value == 1:
pass
# -------------- read data --------------
while bit_count < self.BITS_LEN:
while gpio.value == 0:
pass
# st = time.time()
while gpio.value == 1:
delay_count += 1
# break
if delay_count > self.MAX_DELAY_COUINT:
break
if delay_count > self.BIT_1_DELAY_COUNT:
bits += "1"
else:
bits += "0"
delay_count = 0
bit_count += 1
# -------------- verify --------------
humidity_integer = int(bits[0:8], 2)
humidity_decimal = int(bits[8:16], 2)
temperature_integer = int(bits[16:24], 2)
temperature_decimal = int(bits[24:32], 2)
check_sum = int(bits[32:40], 2)
_sum = humidity_integer + humidity_decimal + temperature_integer + temperature_decimal
# print(bits)
# print(humidity_integer, humidity_decimal, temperature_integer, temperature_decimal)
# print(f'sum:{_sum}, check_sum:{check_sum}')
# print()
if check_sum != _sum:
humidity = 0.0
temperature = 0.0
else:
humidity = float(f'{humidity_integer}.{humidity_decimal}')
temperature = float(f'{temperature_integer}.{temperature_decimal}')
# -------------- return --------------
return humidity, temperature
if __name__ == '__main__':
dht11 = DHT11(17)
while True:
humidity, temperature = dht11.read_data()
print(f"{time.time():.3f} temperature:{temperature}°C humidity: {humidity}%")
time.sleep(2)
**Code Explanation**
.. code-block:: python
def read_data(self):
bit_count = 0
delay_count = 0
bits = ""
# -------------- send start --------------
gpio = OutputDevice(self._pin)
gpio.off()
time.sleep(0.02)
gpio.close()
gpio = InputDevice(self._pin, pull_up=self._pull_up)
#...
This function is used to implement the functions of DHT11. It stores the
detected data in the bits[] array. DHT11 transmits data of 40 bits
at a time. The first 16 bits are related to humidity, the middle 16 bits
are related to temperature, and the last eight bits are used for
verification. The data format is:
**8bit humidity integer data** +\ **8bit humidity decimal data**
+\ **8bit temperature integer data** + **8bit temperature decimal data**
+ **8bit check bit**.
When the validity is detected via the check bit, the function returns
two results: 1. error; 2. humidity and temperature.
.. code-block:: python
_sum = humidity_integer + humidity_decimal + temperature_integer + temperature_decimal
if check_sum != _sum:
humidity = 0.0
temperature = 0.0
else:
humidity = float(f'{humidity_integer}.{humidity_decimal}')
temperature = float(f'{temperature_integer}.{temperature_decimal}')
For example, if the received date is 00101011(8-bit value of humidity
integer) 00000000 (8-bit value of humidity decimal) 00111100 (8-bit
value of temperature integer) 00000000 (8-bit value of temperature
decimal) 01100111 (check bit)
**Calculation:**
00101011+00000000+00111100+00000000=01100111.
If the final result is equal to the check bit data, the data
transmission is abnormal: return False.
If the final result is equal to the check bit data, the received data is
correct, then there will return ``humidity`` and ``temperature`` and output
\"Humidity =43%，Temperature =60C\".