DS18B20 temperature sensor

[michal]

@madsdk
I have tested the library on Wipy 2.0 and it works with stock firmware too. So it has to work on Lopy.

My setup:

Wipy Sensor
3V3 -> red (VCC)
P23 -> yellow (DATA)
GND -> black (GND)
Pull-up resistor 4k7 is connected between VCC and DATA.

Sample code:

>>> import onewire
>>> from machine import Pin
>>> ds = onewire.DS18X20(onewire.OneWire(Pin('P23')))
>>> print('devices:', ds.roms)
devices: [bytearray(b'(\xff\xae8\x90\x15\x03T')]
>>> print('temperatures:', ds.read_temps())
temperatures: [2525]

Michal

[acheesehead]

@michal I have WiPy 2.0 and just upgraded firmware to release 0.9.5.b1. 'import onewire' does not work.

[acheesehead]

Never mind. Uploaded onewire.py to the WiPy 2.0. First got error about the last line that runs test. Commented that out and hooked two sensors up on P23. ds.roms call showed both. ds.read_temps also showed reasonable temps.

Nice!

[madsdk]

@michal Thanks a lot for your answer. I just tried it once more. I have the same setup, except that I had connected the data line to pin 19, which didn't work. When I connect it to pin 23, like you've done, I suddenly get some data from the sensor. I don't think the data I get is correct, but at least I get some data :)

>>> test('P23')
devices: [bytearray(b'(\xc5?6\x07\x00\x00\xba')]
temperatures: [8500]

Why does it work on pin 23 but not on pin 19? I'm fairly new to messing around with hardware on this level :-)

Best regards,
Mads

[Pieter]

Did anyone get it to work and where can i find the related modules? It seems that i need "onewire", "ds18x20" and "pyb". As pyb seem to be more common i can not find a version compatible to LoPy anywhere?

[acheesehead]

I have 3 DS18B20 sensors working with the WiPy 2.0 using the onewire.py module. I'm not sure of the differences between WiPy and LoPy, but it comes down to precision timing, on the order of 6 usec. The WiPy 2.0 (and 1.0) correctly detects the 3 sensors on a single GPIO port.

[Pieter]

@acheesehead can you provide a link to the onewire, ds18x20 and pyb.py files?

[LoneTech]

While I've had success porting the prior micropython bitbanging onewire code (it was mostly changing the IO mode to open drain, and replacing pyb with machine), I just managed to wake up the RMT peripheral. It could conceivably run onewire with extremely precise timing without requiring much CPU. It should only require two RMT channels (one input, one output) mapped on the same GPIO, set to open drain. 6µs should be no problem at all considering I did 0.05µs for the WS2812 :)

The micropython onewire example code is at https://github.com/micropython/micropython/tree/master/drivers/onewire and my initial RMT access code is at https://github.com/lonetech/LoPy

By the way, I suspect the issue with P19 was the bug when accessing GPIO>=31. P19 is GPIO 32.

[JF002]

@LoneTech Would you mind sharing your port of the MicroPython library on the Lopy?It's too bad that this library is not portable across different MicroPython board...
Once I've confirmed that my DS18B20 works fine on the Lopy, I'll try to use the RMT instead of this bitbanging library :)

[LoneTech]

@JF002 Sure. The patch and modules are in http://donkey.vernier.se/~yann/onewire.zip - sorry for taking so long.

[iber]

@LoneTech have you got a working example with the Lopy/Wipy?
When I try to get it working on a Lopy I get a 'OneWire pin didn't go high' error when I run this piece of code d=DS18X20(Pin('G5'))

[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)

[JF002]

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

[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)

[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]

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

[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?

[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)

[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]

@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...