Get Temperature and Humidity from DHT11 module with Raspberry Pi and RPi.GPIO

get-dht11-data.py

import RPi.GPIO as GPIO
import time
import traceback

# Helper
def bin2dec(string_num):
    return str(int(string_num, 2))

def setup_gpio(port):
    GPIO.setmode(GPIO.BCM)

    GPIO.setup(port,GPIO.OUT)

    GPIO.output(port,GPIO.HIGH)
    time.sleep(0.025)
    GPIO.output(port,GPIO.LOW)
    time.sleep(0.02)

    GPIO.setup(port, GPIO.IN, pull_up_down=GPIO.PUD_UP)

def get_dht11_signal_stream(port, number):
    signal_stream = []
    for i in range(0, number):
        signal_stream.append(GPIO.input(port))

    return signal_stream

def cleanup_gpio(port):
    GPIO.cleanup(port)

def divide_into_buckets(signal_stream):
    # Remove first bit + leading 1s, so we can start with our first bucket
    signal_stream = signal_stream[1:]
    cleaned_stream = signal_stream[signal_stream.index(0):]

    buckets = []
    current_bucket = []
    is_one = False

    for bit in cleaned_stream:
        if bit == 0:
            if is_one:
                buckets.append(current_bucket)
                current_bucket = [bit]
                is_one = False
            else:
                current_bucket.append(bit)
        if bit == 1:
            current_bucket.append(bit)
            is_one = True

    return buckets

def interpret_stream(signal_stream):
    buckets = divide_into_buckets(signal_stream)
    output = interpret_buckets(buckets)

    return output

def interpret_buckets(buckets):
    # The DHT11 module sends signals (binary data) in buckets
    # that represent one bit each.
    #
    # E.g.00000000111111111 is a 1 while 0000000111 is a 0
    #
    # The length of the 1s signal determines the bit
    # so when there are more than <bit_threshold> 1s in a bucket
    # it's interpreted as a 1, else as a 0
    bit_threshold = 6

    humidity_bits = ""
    temperature_bits = ""
    crc_bits = ""

    if len(buckets) != 40:
        print str(len(buckets)) + " Buckets found"
        for b in buckets:
            print b
        raise Exception("Bad sensor data")

    # Find out which bucket represents which bit for which measurement
    # 5 times 8 bits:
    #
    # 0 - 7 : Humidity
    # 7 - 15 : Not used here
    # 16 - 24 : Temperature
    # 25 - 31 : Not used here
    # 32 - 39 : Checksum
    for i, bucket in enumerate(buckets):
        num_ones = sum(bucket)
        if i < 8:
            humidity_bits += "1" if num_ones > bit_threshold else "0"
        elif i >= 16 and i < 24:
            temperature_bits += "1" if num_ones > bit_threshold else "0"
        elif i >= 32 and i < 40:
            crc_bits += "1" if num_ones > bit_threshold else "0"

    return {
        "humidity_bits": humidity_bits,
        "temperature_bits": temperature_bits,
        "crc_bits": crc_bits
    }

if __name__ == '__main__':
    port = 4

    # The number of this might vary on your sensor, 800 worked for me
    # Basically this has to be enough to capture all the buckets
    # from the 40 bits the sensor is sending.
    data_count = 1000

    setup_gpio(port)
    signal_stream = get_dht11_signal_stream(port, data_count)
    cleanup_gpio(port)

    output = interpret_stream(signal_stream)

    humidity = bin2dec(output["humidity_bits"])
    temperature = bin2dec(output["temperature_bits"])

    if int(humidity) + int(temperature) - int(bin2dec(output["crc_bits"])) == 0:
        print "Humidity:"+ humidity +"%"
        print "Temperature:"+ temperature +"C"
    else:
        print int(humidity)
        print int(temperature)
        print int(bin2dec(output["crc_bits"]))
        print "ERR_CRC"

I took the version from here: http://www.uugear.com/portfolio/dht11-humidity-temperature-sensor-module/ "reverse-engineered" it to understand what they're doing, refactored it a little and explained it with some comments. If you're trying to connect your Raspberry Pi with a DHT11 module temperature sensor, you might find this helpful!

However, it only works half of the times due to some weird GPIO to python real time issues. So make sure you try the script a bunch of times 😄