Pure Python library for reading DHT sensor on Pycom boards



  • hello,
    from a raspberry pi python library project , i have created a pure python library for pycom board to read the temperature and humidity from a DHT sensor (DTH11, DTH22). I have only tested my library on a pycom sipy esp32 module with a DTH11 sensor. It seems OK , no crash, no error. If someone can try this library with a DTH22 and another pycom board (lopy, wipy), it would be nice.
    The library is on github here

    Update (28/07/2017) :
    There is a new branch in my github repository (pulses_get) here
    only usable from the firmware v1.7.7.b1
    Constructor of the class has changed only pin number is necessary :
    new usage example :

    import pycom
    import time
    from machine import Pin
    from dth import DTH
    pycom.heartbeat(False)
    pycom.rgbled(0x000008) # blue
    th = DTH('P3',0)
    time.sleep(2)
    result = th.read()
    if result.is_valid():
        pycom.rgbled(0x001000) # green
        print("Temperature: %d C" % result.temperature)
        print("Humidity: %d %%" % result.humidity)
    

    Friendly, J.P



  • @Jurassic-Pork The good news is my DHT11 works fine with read(). However I think I bust my DHT22 at some point as reading no data from it. Will have to order another to test..!



  • @robmarkcole
    put this code in the dht.py file and try a read2 in place of a read function. Show me the result (tuples and length) .

        def read2(self):
            #time.sleep(1)
            # send initial high
            #self.__send_and_sleep(1, 0.025)
    
            # pull down to low
            self.__send_and_sleep(0, 0.019)
            data = pycom.pulses_get(self.__pin,100)
            self.__pin.init(Pin.OPEN_DRAIN)
            self.__pin(1)
            print(data)
            #enable_irq(irqf)
            bits = []
            for a,b in data:
            	if a ==1 and 18 <= b <= 28:
            		bits.append(0)
            	if a ==1 and 65 <= b <= 75:
            		bits.append(1)
            print("longueur bits : %d " % len(bits))
            if len(bits) != 40:
                return DTHResult(DTHResult.ERR_MISSING_DATA, 0, 0)
            print(bits)
            # we have the bits, calculate bytes
            the_bytes = self.__bits_to_bytes(bits)
            # calculate checksum and check
            checksum = self.__calculate_checksum(the_bytes)
            if the_bytes[4] != checksum:
                return DTHResult(DTHResult.ERR_CRC, 0, 0)
            # ok, we have valid data, return it
            [int_rh, dec_rh, int_t, dec_t, csum] = the_bytes
            if self.__dhttype==0:		#dht11
                rh = int_rh 		#dht11 20% ~ 90%
                t = int_t 	#dht11 0..50°C
            else:			#dht21,dht22
                rh = ((int_rh * 256) + dec_rh)/10
                t = (((int_t & 0x7F) * 256) + dec_t)/10
                if (int_t & 0x80) > 0:
                    t *= -1
            return DTHResult(DTHResult.ERR_NO_ERROR, t, rh)
    

    PS : i have created a new branch in my DHT_pycom github repository (see at the end of my first message in this thread)



  • @Jurassic-Pork I just updated my firmware today :-) How to use the new function?



  • hello,
    @robmarkcole have you still your problem ? the new firmware release v1.7.7.b1 have a new function pulses_get that can improve my DHT library.





  • @robmarkcole
    try this :

    import machine
    import os
    machine.freq() # get the CPU frequency
    os.uname().release 
    

    for me :

    import machine                                                                                                      
     import os                                                                                                           
     machine.freq() # get the CPU frequency                                                                              
    160000000                                                                                                               
     os.uname().release                                                                                                  
    '1.6.12.b1'



  • Hi @Jurassic-Pork

    • it's a Wipy 2.0,
    • will check firmware tonight but only updated 2 days ago so presumably the latest,
    • how to check the frequency?


  • hello,
    @robmarkcole
    Ok it's not good because you have only 39 values (last line)
    it's seems that your module is slower than mine because the max value for length of 1 level is 4 and for me 5 (or it is the dht ) . What is exactly your Pycom Module ? frequency ? firmware ?



  • @Jurassic-Pork said in Pure Python library for reading DHT sensor on Pycom boards:

    state = STATE_INIT_PULL_DOWN

    Thanks JP. Making this change I get:

    entry 0x4009fd9c                                                                                                        
    ('192.168.0.23', '255.255.255.0', '192.168.0.1', '192.168.0.1')                                                         
    [1, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 1, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0,
     1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 1, 1, 0,
     0, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1,
     0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1,
     0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
     1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
     1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]                                             
    [1, 1, 3, 2, 3, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 2, 1, 2, 3, 1, 1, 1, 2, 1, 2, 1, 2, 1, 1, 3, 1, 1, 3, 4, 3]   
    39  
    

    And nothing more



  • hello,
    @robmarkcole
    0_1496785483210_dht11_timing_diagram_cs600x210fx.png

    May be you have the Delay DHT in your first data and not me.

    In the parse data function :

        def __parse_data_pull_up_lengths(self, data):
            STATE_INIT_PULL_DOWN = 1
            STATE_INIT_PULL_UP = 2
            STATE_DATA_FIRST_PULL_DOWN = 3
            STATE_DATA_PULL_UP = 4
            STATE_DATA_PULL_DOWN = 5
    
            state = STATE_INIT_PULL_UP
    
            lengths = [] # will contain the lengths of data pull up periods
            current_length = 0 # will contain the length of the previous period
    
            for i in range(len(data)):
    
                current = data[i]
                current_length += 1
    
                if state == STATE_INIT_PULL_DOWN:
                    if current == 0:
                        # ok, we got the initial pull down
                        state = STATE_INIT_PULL_UP
                        continue
                    else:
                        continue
                if state == STATE_INIT_PULL_UP:
                    if current == 1:
                        # ok, we got the initial pull up
                        state = STATE_DATA_FIRST_PULL_DOWN
                        continue
                    else:
                        continue
                if state == STATE_DATA_FIRST_PULL_DOWN:
                    if current == 0:
                        # we have the initial pull down, the next will be the data pull up
                        state = STATE_DATA_PULL_UP
                        continue
                    else:
                        continue
                if state == STATE_DATA_PULL_UP:
                    if current == 1:
                        # data pulled up, the length of this pull up will determine whether it is 0 or 1
                        current_length = 0
                        state = STATE_DATA_PULL_DOWN
                        continue
                    else:
                        continue
                if state == STATE_DATA_PULL_DOWN:
                    if current == 0:
                        # pulled down, we store the length of the previous pull up period
                        lengths.append(current_length)
                        state = STATE_DATA_PULL_UP
                        continue
                    else:
                        continue
            return lengths
    

    try to put the state variable to STATE_INIT_PULL_DOWN at the begining of the function :

     state = STATE_INIT_PULL_DOWN
    

    Friendly, J.P



  • @Jurassic-Pork Appears to always start with 1..



  • hello,
    @robmarkcole
    look at this this timing for the AM2302 data acquisition :
    0_1496762177466_AM2302-Timing.png
    the acquisition begins when the start signal after 19 ms is put to level 1 :

    def read(self):
            #time.sleep(1)
            # send initial high
            #self.__send_and_sleep(1, 0.025)
            # pull down to low
            self.__send_and_sleep(0, 0.019)
            # collect data into an array
            data = self.__collect_input()
    
        def __collect_input(self):
            # collect the data while unchanged found
            unchanged_count = 0
            # this is used to determine where is the end of the data
            max_unchanged_count = 100
            last = -1
            data = []
            m = bytearray(800)        # needs long sample size to grab all the bits from the DHT
            irqf = disable_irq()
            self.__pin(1)
    

    then we store the level values :

           for i in range(len(m)):
                m[i] = self.__pin()      ## sample input and store value
    

    your samples data begin with a 1 and me with a zero (begining of the response signal)
    try to see if you have always a 1 for the first data.



  • Hi @Jurassic-Pork thanks for the tips. Here is what I get. The temp and humidity values change each time I reset the board, but look incorrect. E.g. humidity went from 18 to 37 on a restart.
    Cheers

    entry 0x4009fd9c                                                                                                        
    ('192.168.0.23', '255.255.255.0', '192.168.0.1', '192.168.0.1')                                                         
    [1, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 1,
     1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0,
     0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
     1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1,
     1, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1,
     1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
     1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
     1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]                                                                  
    [2, 2, 3, 2, 1, 4, 1, 4, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 4, 1, 1, 4, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 4, 4, 1, 4, 4, 4]
    40                                                                                                                      
    [37, 0, 18, 0, 55]                                                                                                      
    8                                                                                                                       
    Temperature: 18 C                                                                                                       
    Humidity: 37 %



  • hello,
    @robmarkcole
    to see what is wrong, you can uncomment some lines in the file dht.py. The lines 49, 53, 54, 63 with the print function.
    you must see something like that for the dht11 :
    0_1496716130654_print_dht11_data.png

    the last line in the photo (line 63 print(the_bytes)) has the values for the humidity (32) and for the temperature (22).
    May be something is wrong with the WiPy module :
    i use a SiPy module and the other people who have used the library seems to use a LoPy module. If someone can try to use the library with a WiPy module to see if it is OK.

    Friendly, J.P



  • Annoyingly I am unable to upload the code, as it is 'marked as spam' when I try. Nevertheless I am just using the examples in your Github repo



  • @RobTuDelft I would, but I only have 1 and 10 k Ohm available at the moment.

    0_1496691300215_upload-20d267d5-acb8-46c0-9a1b-92b7165af7a6



  • @robmarkcole Can you try it with a 4k7 resistor, maybe 10k is too much? You could also post a picture of your setup and the code fragments you are using.



  • @RobTuDelft Yes used those. Humidity and temp constant. Swapped in a DHT11 now and seeing same behaviour. Any tips on how to debug?
    Cheers



  • @robmarkcole that one I forked from JP. I was using a 4k7 resistor and it worked well.

    Do you have print('Humidity: {:3.2f}'.format(result.humidity / 1.0))? And
    You did declare the sensor object as th = DTH(Pin('P3', mode=Pin.OPEN_DRAIN), 1)? The last one declares it as a DHT22.

    Does the humidity fluctuate at all?


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