Pure Python library for reading DHT sensor on Pycom boards

Jurassic Pork

@palmy-nz
on the photo , it seems that you have wired the dht11 in a strange manner.
alt text

it must be :
3.3v on pin 1
signal on pin 2
gnd on pin 4

may be it is not the same chip.

palmy-nz

@Jurassic-Pork
I am using this DHT11 sensor...
https://pasteboard.co/e4ZITp59g.png
This image just made me realize the pull up resistor is already embedded.
I have removed the resistor i had in my circuit, but still the same problem.

Jurassic Pork

@palmy-nz
ok it seems good for your module and you have a pull up resistor on your module.
be careful if you have powered your module with 5v may be you have the signal pin on your pycom module out of order. Try to check it without the dht11 module (input level 0 (gnd) input level 1 (pull up resistor to 3.3v)).

palmy-nz

@Jurassic-Pork
I got it working now. the problem was i was running an older firmware, after updating to latest, it seems to be working now.
Thanks to @livius for troubleshooting it with me.
and @Jurassic-Pork for the library.
This is a great forum.

robmarkcole

@RobTuDelft in Pure Python library for reading DHT sensor on Pycom boards:

Hi Rob, using your library (https://github.com/rbraggaar/DHT_PyCom), DHT22 on Wipy with 10 kOhm pullup, I am getting a temp of 25 deg (correct) but humidity of 99.9% (incorrect). Any ideas what could be wrong?
Cheers

RobTuDelft

@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?

robmarkcole

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

RobTuDelft

@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.

robmarkcole

@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

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

Jurassic Pork

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 :

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

robmarkcole

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 %

Jurassic Pork

hello,
@robmarkcole
look at this this timing for the AM2302 data acquisition :

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.

robmarkcole

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

Jurassic Pork

hello,
@robmarkcole

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

robmarkcole

@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

Jurassic Pork

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 ?

robmarkcole

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?

Jurassic Pork

@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'

robmarkcole

@Jurassic-Pork s

0_1496904069365_upload-4c762e17-60b1-4129-82b3-268d0666a29a

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Pure Python library for reading DHT sensor on Pycom boards

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