Raspberry Pi reads DHT11 temperature and humidity data in Python

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Raspberry Pi 4: Reading Temperature and Humidity Data from DHT11 Sensor via GPIO Using Python

Introduction

The DHT11 is a temperature and humidity sensor with a calibrated digital signal output. Its accuracy is ±5% RH for humidity and ±2°C for temperature, with a measurement range of 20–90% RH for humidity and 0–50°C for temperature. Although its accuracy is low, it is very inexpensive. The DHT11 uses a single-wire communication protocol and operates on a supply voltage of 3.3–5V.

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Reading DHT11, DHT22, and SHTC3 temperature and humidity data with Arduino: https://blog.zeruns.com/archives/527.html
Python method for microsecond-level delays: https://blog.zeruns.com/archives/623.html

DHT11 Datasheet Download: https://url.zeruns.com/DHT11 Password: qefk

Source Code

Wiring Connection:

I am using a Raspberry Pi 4; for other models, please check and adjust accordingly.

Raspberry Pi 4 GPIO Pinout: https://url.zeruns.com/RPI4_GPIO

DHT11		Raspberry Pi
 VCC---------5V (Pin 2)
 DATA-------BCM18 (BCM pin 18, which is physical pin 12)
 GND--------Ground (Pin 6)

Source Code:

import RPi.GPIO as GPIO
import time

def delayMicrosecond(t):    # Microsecond delay function
    start, end = 0, 0       # Declare variables
    start = time.time()     # Record start time
    t = (t - 3) / 1000000   # Convert input t to seconds; -3 is time compensation
    while end - start < t:  # Loop until time difference is greater than or equal to the set value
        end = time.time()   # Record end time

tmp = []      # Store read data

data = 18     # DHT11 data pin connected to Raspberry Pi GPIO pin (BCM numbering)
# https://blog.zeruns.com  
a, b = 0, 0

def DHT11():
    GPIO.setup(data, GPIO.OUT)  # Set GPIO pin as output
    GPIO.output(data, GPIO.HIGH) # Set GPIO output to high level
    delayMicrosecond(10 * 1000) # Delay 10 milliseconds
    GPIO.output(data, GPIO.LOW)  # Set GPIO output to low level
    delayMicrosecond(25 * 1000)  # Delay 25 milliseconds        
    GPIO.output(data, GPIO.HIGH) # Set GPIO output to high level
    GPIO.setup(data, GPIO.IN)    # Set GPIO pin as input
# https://blog.zeruns.com     
    a = time.time()           # Record loop start time
    while GPIO.input(data):   # Keep looping until input becomes low
        b = time.time()       # Record end time
        if (b - a) > 0.1:     # Check if loop duration exceeds 0.1 seconds to avoid infinite loop
            break             # Exit loop
         
    a = time.time()
    while GPIO.input(data) == 0:  # Keep looping until input becomes high
        b = time.time()
        if (b - a) > 0.1:
            break
                 
    a = time.time()
    while GPIO.input(data): # Keep looping until input becomes low
        b = time.time()
        if (b - a) >= 0.1:
            break   
             
    for i in range(40):         # Loop 40 times to receive temperature and humidity data
        a = time.time()
        while GPIO.input(data) == 0:  # Keep looping until input becomes high
            b = time.time()
            if (b - a) > 0.1:
                break
# https://blog.zeruns.com                         
        delayMicrosecond(28)    # Delay 28 microseconds
             
        if GPIO.input(data):    # After 28 microseconds, check if still high
            tmp.append(1)       # Record received bit as 1
                 
            a = time.time()
            while GPIO.input(data): # Keep looping until input becomes low
                b = time.time()
                if (b - a) > 0.1:
                    break
        else:
            tmp.append(0)       # Record received bit as 0
             
while True:
    GPIO.setmode(GPIO.BCM)      # Set to BCM numbering mode
    GPIO.setwarnings(False)
    del tmp[0:]                 # Clear list
    time.sleep(1)               # Delay 1 second
# https://blog.zeruns.com     
    DHT11()
  
    humidity_bit = tmp[0:8]       # Split list: bits 0–7 are integer humidity data
    humidity_point_bit = tmp[8:16]# Humidity decimal
    temperature_bit = tmp[16:24]  # Temperature integer
    temperature_point_bit = tmp[24:32]    # Temperature decimal
    check_bit = tmp[32:40]        # Checksum data
 
    humidity_int = 0
    humidity_point = 0
    temperature_int = 0
    temperature_point = 0
    check = 0
# https://blog.zeruns.com  
    for i in range(8):          # Convert binary to decimal
        humidity_int += humidity_bit[i] * 2 ** (7 - i)
        humidity_point += humidity_point_bit[i] * 2 ** (7 - i)
        temperature_int += temperature_bit[i] * 2 ** (7 - i)
        temperature_point += temperature_point_bit[i] * 2 ** (7 - i)
        check += check_bit[i] * 2 ** (7 - i)
  
    humidity = humidity_int + humidity_point / 10
    temperature = temperature_int + temperature_point / 10
  
    check_tmp = humidity_int + humidity_point + temperature_int + temperature_point
  
    if check == check_tmp and temperature != 0 and humidity != 0:  # Check if data is valid
        print("Temperature is ", temperature, "C\nHumidity is ", humidity, "%") # Print temperature and humidity
        print("https://blog.zeruns.com")
    else:
        print("error")
  
    time.sleep(1)
    GPIO.cleanup()

Result Images

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