Raspberry PI DHT Sensor Control Code

DHT sensors can measure temperature and humidity. You can receive fresh measurements every 2 seconds in the form of digital signals. DHT11 can sense temperature from 0 to 50 °C and humidity from 20 to 80% RH. DHT22 can sense temperature from -40 to 80 °C and humidity from 0 to 100% RH. The DHT Controller Device manages communication between a DHT sensor and the current Ozeki software.

raspberry pi with dht sensors
Figure 1 - Raspberry PI with DHT11 or DHT22 sensor

Required hardware

  • Raspberry PI
  • DHT11 or DHT22 sensor
  • Resistor 4.7kΩ

Source code to install on controller

#!/usr/bin/python
# -*- coding: utf-8 -*-

import RPi.GPIO as GPIO
import time
import sys

def bin2dec(string_num):
    return str(int(string_num, 2))
   
data = []
effectiveData = []
bits_min=999;
bits_max=0;
HumidityBit = ""
TemperatureBit = ""
crc = ""
crc_OK = False;
Humidity = 0
Temperature = 0

pin=17

GPIO.setmode(GPIO.BCM)

def pullData():
    global data
    global effectiveData
    global pin
    
    data = []
    effectiveData = []
    
    GPIO.setup(pin,GPIO.OUT)
    GPIO.output(pin,GPIO.HIGH)
    time.sleep(0.025)
    GPIO.output(pin,GPIO.LOW)
    time.sleep(0.14)
    
    GPIO.setup(pin, GPIO.IN, pull_up_down=GPIO.PUD_UP)
    
    for i in range(0,1000):
        data.append(GPIO.input(pin))

def analyzeData():    
    seek=0;
    bits_min=9999;
    bits_max=0;

    global HumidityBit
    global TemperatureBit
    global crc
    global Humidity
    global Temperature

    HumidityBit = ""
    TemperatureBit = ""
    crc = ""
    
    while(seek < len(data) and data[seek] == 0):
        seek+=1;
    
    while(seek < len(data) and data[seek] == 1):
         seek+=1;
    
    for i in range(0, 40):
        
        buffer = "";
        
        while(seek < len(data) and data[seek] == 0):
            seek+=1;
        
        
        while(seek < len(data) and data[seek] == 1):
            seek+=1;
            buffer += "1";
        
        if (len(buffer) < bits_min):
            bits_min = len(buffer)
    
        if (len(buffer) > bits_max):
            bits_max = len(buffer)
        
        effectiveData.append(buffer);
            
    for i in range(0, len(effectiveData)):
        if (len(effectiveData[i]) < ((bits_max + bits_min)/2)):
            effectiveData[i] = "0";
        else:
            effectiveData[i] = "1";
    
    for i in range(0, 8):
        HumidityBit += str(effectiveData[i]);
    
    for i in range(16, 24):
        TemperatureBit += str(effectiveData[i]);
    
    
    for i in range(32, 40):
        crc += str(effectiveData[i]);
    
    Humidity = bin2dec(HumidityBit)
    Temperature = bin2dec(TemperatureBit)

def isDataValid():
    global Humidity
    global Temperature
    global crc
    
    if int(Humidity) + int(Temperature) == int(bin2dec(crc)):
        return True;
    else:
        return False;

def printData():
   global Humidity
   global Temperature
   
   print "{}\t{}\t".format ("Humidity: ", Humidity + "%")
   print "{}\t{}\t".format ("Temperature: ", Temperature + "°C")

try:
    while True:
        pullData();
        analyzeData();
        if (isDataValid()):
            crc_OK=True;
            print "\r",
            printData();
        else:
            sys.stderr.write(".")
            time.sleep(2);

except KeyboardInterrupt:
    GPIO.cleanup()

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