DS18B20 temperature sensor

[madsdk]

I'd like to read the temperature from my LoPy using a DS18B20 sensor. My problem is that this is a digital sensor using the 1-wire protocol, and as far as I can tell, there's no 1-wire library on the LoPy? Looking at the Micro Python documentation (https://docs.micropython.org/en/latest/esp8266/esp8266/tutorial/onewire.html) I see that they've got a onewire module, they've even got a ds18x20 module, but that's not available on my LoPy I think. I've been searching the Internet looking for a suitable 1-wire library, but so far without any luck. I can find some that require libusb or the like, but that won't work I assume.

Does anyone know how I should go about reading from a 1-wire sensor on a LoPy?

Best regards,
Mads

[jimpower]

@livius thanks that did the trick

[livius]

@jimpower
better look here
https://github.com/pycom/pycom-libraries/tree/master/examples/DS18X20

[jimpower]

@dchappel I followed your main.py with both onewire.py and ds18x20.py in my lib, this works for the first temp reading, every following temp reading doesn't change from the first. I moved the sensor into the fridge and then freezer and the readings styed the same. Once I reset the device it will bring the new reading but only again for the first reading. Did you find this with yours?

[livius]

@soren

1. what you got from (you must change P10 to pin you use):

ow = OneWire(Pin('P10'))
ow.roms

if nothing then test(double ow)

ow.ow.scan()

1. which sensor do you have exactly? woterproof or some different?

[soren]

@livius said in DS18B20 temperature sensor:

https://github.com/pycom/pycom-libraries/blob/master/lib/onewire/onewire.py

When I do exactly as you state here, and connect the temperature sensor to 3.3v, and with the 4,7k resistor between sig and 3.3v - I get this error:

File "main.py", line 22, in <module>
File "/flash/lib/onewire.py", line 190, in read_temp_async
IndexError: list index out of range

I have latest firmware and atom plugin

EDIT: after checking that I have latest onewire from here https://github.com/pycom/pycom-libraries/blob/master/lib/onewire/onewire.py this error was gone. I then had to correct your spelling mistake in "convertion" and now it's working, but despite everything being hooked up correctly - it prints out "None"...

[Guizmolux]

@livius
it didn't seem to work with Pymakr. The Atom IDE with Pymakr pluggin solution that was updated as a tutorial last week definitely helped.
It seems to be good now.
Thank you!

[livius]

@Guizmolux

but do you have upgraded firmware?
current is 1.6.12.b1
what is yours? you can check firmware version by

os.uname()

if it is really old then go to
https://www.pycom.io/resources/

next, is this how your onewire looks like?
https://github.com/pycom/pycom-libraries/blob/master/lib/onewire/onewire.py

put it in the same place where you have main.py or in lib subfolder

and then you can simply use it

import time
from machine import Pin
from onewire import DS18X20
from onewire import OneWire

#DS18B20 data line connected to pin P10
ow = OneWire(Pin('P10'))
temp = DS18X20(ow)

while True:
    print(temp.read_temp_async())
    time.sleep(1)
    temp.start_convertion()
    time.sleep(1)

[Guizmolux]

@livius
I get that. Copied the code into a onewire.py file. Where should I put it?
I've tried to execute before the main.py file and I always get the "cannot import name OneWire" or "DS18X20".
is the const() a problem in class OneWire ?

[livius]

@Guizmolux
I do not know if you ask for this
but fully working examlpe code you can find in official docs
https://docs.pycom.io/pycom_esp32/pycom_esp32/tutorial/includes/onewire.html

[Guizmolux]

@dchappel
I'm very new to this (and LoPy and python) : where is your lib directory ?(I'll adapt to my own config).

[dchappel]

@DonHugo

(sysname='LoPy', nodename='LoPy', release='1.5.1.b1', version='v1.8.6-423-g18444a2 on 2017-02-07', machine='LoPy with ESP32', lorawan='1.0.0')

The pin not going high message sounds more like a wiring issue? Are you sure your wiring is correct and the pullup resistor bridges +3.3V and data? I had same issue and realized that I had sensor wire colors mixed up...

[DonHugo]

@dchappel i cant get this to work, i get

# code block
Running 
Traceback (most recent call last):
  File "<stdin>", line 7, in <module>
  File "ds18x20.py", line 47, in __init__
  File "onewire.py", line 246, in scan
  File "onewire.py", line 269, in _search
  File "onewire.py", line 90, in reset
OSError: OneWire pin didn't go high
>
MicroPython v1.8.6-464-g0f843911 on 2017-02-17; LoPy with ESP32
Type "help()" for more information.

what firmware are you using?

[dchappel]

@sk

onewire.py and ds18x20.py are in my lib directory (available here per @LoneTech: http://donkey.vernier.se/~yann/onewire.zip)

This works for me:

import time
from machine import Pin
from ds18x20 import DS18X20

while True:
    
    d=DS18X20(Pin('P23', mode=Pin.OUT))
    
    result=(d.read_temps())
    
    if result:
        val=str(result[0]*1.8+32)
    else:
        val="-1"
        
    print(val)
    
    time.sleep(5)

[sk]

@iber how did you import the ds18x20 module? I am getting the error:

Traceback (most recent call last):
File "<stdin>", line 2, in <module>
ImportError: no module named 'ds18x20'

I have pasted the ds18x20.py into the folder my other py files and project is in. Is that not where it goes?

[Colateral]

@madsdk P23/G10 has SD_CLK (pulse clock) required for bit banging.

[Colateral]

@Colateral I checked the code an conv_temp function shall be changed as following

def convert_temp(self, rom0, data):
    """
    Convert the raw temperature data into degrees celsius and return as a fixed point with 2 decimal places.
    """
    temp_lsb = data[0]
    temp_msb = data[1]
    if rom0 == 0x10:
        if temp_msb != 0:
            # convert negative number
            temp_read = temp_lsb >> 1 | 0x80  # truncate bit 0 by shifting, fill high bit with 1.
            temp_read = -((~temp_read + 1) & 0xff) # now convert from two's complement
        else:
            temp_read = temp_lsb >> 1  # truncate bit 0 by shifting
        count_remain = data[6]
        count_per_c = data[7]
        temp = 100 * temp_read - 25 + (count_per_c - count_remain) // count_per_c
        return temp
    elif rom0 == 0x28:
        temp = (temp_msb << 8 | temp_lsb) / 16
        if (temp_msb & 0xf8) == 0xf8 :  # for negative temperature
           temp -= 0x1000

        return temp * 1000
    else:
        assert False

[Colateral]

@michal The temperature output(2525 = 25.25 degrees celsius) is as 4 digits output. The strange fact is that If I read the same sensor with raspberry pi or on Arduino I got the value as 5 digits. (eq 25437)

[JF002]

@LoneTech Thank you! I'll give it a try as soon as I have time :)

[iber]

I got it working now.

from machine import Pin
from ds18x20 import DS18X20
d=DS18X20(Pin('G17', mode=Pin.OUT))
result=d.read_temps()
print(result)