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Raspberry Pi with DHT11/22

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Introduction

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In this lesson, you will learn how to connect and read data from a DHT11/22 temperature and humidity sensor using a Raspberry Pi.

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Some (analog) sensors can work with the Raspberry Pi without needing external ADC – through the help of software libraries. An example of such sensors is a DHT sensor.

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A DHT sensor (Digital Humidity and Temperature sensor) is commonly used for measuring temperature and humidity in various applications. There are two popular versions:​

  • DHT11 and DHT22

Sensori-DHT11-e-DHT22.jpg

DHT11/22 Pinout

​Needed Components:

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  • Raspberry Pi 5

  • DHT22 or DHT11

  • Breadboard

  • Jumper wires

  • 10k ohms resistor 

​

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Both sensors communicate via a single-wire protocol, making them easy to interface with microcontrollers like the Arduino and Raspberry Pi.

Circuit Diagram

5mWGFsGhbx.png

DHT22 Sensor module connected to Pin21 of Raspberry Pi 5

uVSgN3XgeZ.png

DHT22 Sensor (with 10K resistor) connected to  Raspberry Pi 5

DHT22 Programming

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Now install the DTOVERLAY DHT22 or DHT11 depending on the model you have (we will be using GPIO21 in this example):

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  • Open Raspberry Pi Terminal and type: type “sudo nano /boot/firmware/config.txt”

  • Navigate down using the “down arrow button” to where you have [All]

  • Just after the [ALL] add this line: “dtoverlay=dht22,gpiopin=21” then click “Enter”

  • Press CTRL+X then type “yes” to save, then click “Enter”

  • Type “sudo reboot” then “Enter” to reboot your Pi and activate changes.

 

Once your Pi is back up, write the following Python code to read values from your dht22 sensor:

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dht22.py code:

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#!/bin/python3
import time

device0 = "/sys/bus/iio/devices/iio:device0"

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#function to read the first line and return integer
def readFirstLine(filename):
    try:
        f = open(filename,"rt")
        value =  int(f.readline())
        f.close()
        return True, value
    except ValueError:
        f.close()
        return False,-1
    except OSError:
        return False,0

​

try:
    while True:
        Flag, Temperature = readFirstLine(device0+"/in_temp_input")
        print("Temperature:",end="")
        if Flag:
            print(Temperature // 1000,"\u2103",end="\t")
        else:
            print("N.A.",end="\t")

        Flag, Humidity = readFirstLine(device0+"/
               in_humidityrelative_input")
        print("Humidity:",end="")
        if Flag:
            print(Humidity // 1000,"%")
        else:
            print("N.A.")
        time.sleep(2.0)
except KeyboardInterrupt:
    pass

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