Re: [weewx-user] Error in Humidity in Wundergound Post

[jardiamj]

On Tue, 2019-09-03 at 09:16 -0700, William Webb wrote:
> I see in the Davis Monitor II driver how to get the two byte checksum
> from the weather station. Can you point me to an example of how to
> calculate the checksum from the data bytes for comparison? A Python
> example would probably give me enough information to modify the
> driver. 
> 

Hi Bill,

The implementation for the CRC checksum calculation is here:
https://github.com/weewx/weewx/blob/master/bin/weewx/crc16.py

I'll send you a private email with a gzipped tarball of the technical
reference files that I used when writing the driver. This mailing list
is not letting me add the attachment to this message.

Let me know if you find any bugs in the driver.

Jardi.

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Re: [weewx-user] Error in Humidity in Wundergound Post

[Thomas Keffer]

No idea what the WMII does for a checksum. Possibilities

   1. A simple XOR'ing of the bytes. But, this would leave you with a 1
   byte checksum, and it seems the WMII uses 2 bytes. I don't think they would
   XOR 2 bytes at a time, because then you would have to worry about the
   "endianness" of the machine you're running on.
   2. Much more likely, it's the same algorithm used by the Davis Vantage
   series. See the implementation in the file weewx/crc16.py
   .

-tk

On Tue, Sep 3, 2019 at 9:16 AM William Webb  wrote:

> I see in the Davis Monitor II driver how to get the two byte checksum from
> the weather station. Can you point me to an example of how to calculate the
> checksum from the data bytes for comparison? A Python example would
> probably give me enough information to modify the driver.
>
> --
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> "weewx-user" group.
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> To view this discussion on the web visit
> https://groups.google.com/d/msgid/weewx-user/3102da13-fda4-4842-aac0-96897e8515ee%40googlegroups.com
> .
>

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Re: [weewx-user] Error in Humidity in Wundergound Post

[William Webb]

I see in the Davis Monitor II driver how to get the two byte checksum from the 
weather station. Can you point me to an example of how to calculate the 
checksum from the data bytes for comparison? A Python example would probably 
give me enough information to modify the driver. 

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Re: [weewx-user] Error in Humidity in Wundergound Post

[Thomas Keffer]

Looking at KCAORANG21, the WU is receiving low values for pressure on the
hour, although with the WU, you never really know. But, given that you are
cycling the wifi adapter at exactly the same time, odds are that the
problem is on your end, rather than on the WU end.

I am not familiar with the wmii driver but, looking through its code, it
ignores the checksum, so it's entirely possible it is receiving a bad
packet on the hour, which gets decoded into nonsense values. The many bad
values logged give evidence to this theory. For example,

Sep  1 08:29:17 raspberrypi weewx[425]: engine: 2019-09-01 08:29:17 PDT
(1567351757) LOOP value 'pressure' -29.33 outside limits (24.0, 34.5)
Sep  1 08:29:17 raspberrypi weewx[425]: engine: 2019-09-01 08:29:17 PDT
(1567351757) LOOP value 'outHumidity' 128 outside limits (0.0, 100.0)
Sep  1 08:29:17 raspberrypi weewx[425]: engine: 2019-09-01 08:29:17 PDT
(1567351757) LOOP value 'outTemp' 3276.7 outside limits (-40.0, 120.0)
Sep  1 08:29:18 raspberrypi weewx[425]: engine: 2019-09-01 08:29:18 PDT
(1567351758) LOOP value 'pressure' -29.33 outside limits (24.0, 34.5)
Sep  1 08:29:18 raspberrypi weewx[425]: engine: 2019-09-01 08:29:18 PDT
(1567351758) LOOP value 'outHumidity' 128 outside limits (0.0, 100.0)

So, when weewx calculates the average pressure for the interval, it gets an
off value. Incidentally, you're getting low values for other types, such as
outside temperature. They are probably suffering from the same problem.

You should contact the author of the driver. It really should use the
checksum. Garbage in, garbage out! :-)

-tk

On Mon, Sep 2, 2019 at 8:14 AM William Webb  wrote:

> You are correct I somehow got fixated on Humidity.  The issue is
> pressure.  My station is KCAORANG21.  My log is attached.
>
> On Monday, September 2, 2019 at 7:27:05 AM UTC-7, Thomas Keffer wrote:
>>
>> I'm not sure what we're looking at here. It looks more a plot of
>> barometric pressure, rather than humidity.
>>
>> Or, is the issue the plot on the top (which is always zero)?
>>
>> Your WU station ID would be helpful. And, of course, the log. See the
>> wiki article *Help! Posting to weewx-user
>> *.
>>
>> In short, you're not giving us much information.
>>
>>
>>
>>
>> On Mon, Sep 2, 2019 at 7:00 AM William Webb  wrote:
>>
>>> This is a perplexing problem.  I don't know enough about the structure
>>> of weewx code or the Davis Monitor II driver to hazard a guess.  My
>>> station, a Davis Monitor II, running on a Raspberry PI B+ appears to be
>>> working fine without drama.  The PI has an IP assigned outside of DHCP on a
>>> Spectrum Gateway router. I have always had stability issues between PIs and
>>> Spectrum.  I have avoided the random disconnects by running this on the
>>> hour as a chron task.
>>>
>>> #!/bin/bash
>>>
>>> sudo ifconfig wlan0 down
>>>
>>> sudo ifconfig wlan0 up
>>>
>>> sudo service networking restart
>>>
>>>
>>>  I let the setup run several days before enabling posting to
>>> Wundergound.  My data when views on the web site locally looked fine.  When
>>> I looked at my data on WundergroundI discovered an anomaly with humidity.
>>> After the chron task ran the humidity read low for one reading.
>>>
>>> [image: Wu_report.jpg]
>>>
>>>
>>> This is beyond weird. Only humidity is off and it is only the first
>>> reading after the network reconnect.  What could be wrong?  Have I
>>> discovered some really subtle bug?  If you folks think so, I can repost on
>>> the development forum.
>>>
>>>
>>> Bill - AB6OR
>>>
>>>
>>>
>>>
>>> --
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>>> Groups "weewx-user" group.
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>>> 
>>> .
>>>
>> --
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> 
> .
>

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Re: [weewx-user] Error in Humidity in Wundergound Post

[William Webb]

P.S for now I shut down the Chron task.

Bill

On Monday, September 2, 2019 at 8:14:43 AM UTC-7, William Webb wrote:
>
> You are correct I somehow got fixated on Humidity.  The issue is 
> pressure.  My station is KCAORANG21.  My log is attached.
>
> On Monday, September 2, 2019 at 7:27:05 AM UTC-7, Thomas Keffer wrote:
>>
>> I'm not sure what we're looking at here. It looks more a plot of 
>> barometric pressure, rather than humidity.
>>
>> Or, is the issue the plot on the top (which is always zero)?
>>
>> Your WU station ID would be helpful. And, of course, the log. See the 
>> wiki article *Help! Posting to weewx-user 
>> *.
>>
>> In short, you're not giving us much information.
>>
>>
>>
>>
>> On Mon, Sep 2, 2019 at 7:00 AM William Webb  wrote:
>>
>>> This is a perplexing problem.  I don't know enough about the structure 
>>> of weewx code or the Davis Monitor II driver to hazard a guess.  My 
>>> station, a Davis Monitor II, running on a Raspberry PI B+ appears to be 
>>> working fine without drama.  The PI has an IP assigned outside of DHCP on a 
>>> Spectrum Gateway router. I have always had stability issues between PIs and 
>>> Spectrum.  I have avoided the random disconnects by running this on the 
>>> hour as a chron task.
>>>
>>> #!/bin/bash
>>>
>>> sudo ifconfig wlan0 down
>>>
>>> sudo ifconfig wlan0 up
>>>
>>> sudo service networking restart
>>>
>>>  
>>>  I let the setup run several days before enabling posting to 
>>> Wundergound.  My data when views on the web site locally looked fine.  When 
>>> I looked at my data on WundergroundI discovered an anomaly with humidity.  
>>> After the chron task ran the humidity read low for one reading.
>>>
>>> [image: Wu_report.jpg]
>>>
>>>
>>> This is beyond weird. Only humidity is off and it is only the first 
>>> reading after the network reconnect.  What could be wrong?  Have I 
>>> discovered some really subtle bug?  If you folks think so, I can repost on 
>>> the development forum.
>>>
>>>
>>> Bill - AB6OR
>>>
>>>
>>>
>>>
>>> -- 
>>> You received this message because you are subscribed to the Google 
>>> Groups "weewx-user" group.
>>> To unsubscribe from this group and stop receiving emails from it, send 
>>> an email to weewx...@googlegroups.com.
>>> To view this discussion on the web visit 
>>> https://groups.google.com/d/msgid/weewx-user/1b8556bc-ea98-4b1c-b97d-06a95d075631%40googlegroups.com
>>>  
>>> 
>>> .
>>>
>>

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Re: [weewx-user] Error in Humidity in Wundergound Post

[Thomas Keffer]

I'm not sure what we're looking at here. It looks more a plot of barometric
pressure, rather than humidity.

Or, is the issue the plot on the top (which is always zero)?

Your WU station ID would be helpful. And, of course, the log. See the wiki
article *Help! Posting to weewx-user
*.

In short, you're not giving us much information.




On Mon, Sep 2, 2019 at 7:00 AM William Webb  wrote:

> This is a perplexing problem.  I don't know enough about the structure of
> weewx code or the Davis Monitor II driver to hazard a guess.  My station, a
> Davis Monitor II, running on a Raspberry PI B+ appears to be working fine
> without drama.  The PI has an IP assigned outside of DHCP on a Spectrum
> Gateway router. I have always had stability issues between PIs and
> Spectrum.  I have avoided the random disconnects by running this on the
> hour as a chron task.
>
> #!/bin/bash
>
> sudo ifconfig wlan0 down
>
> sudo ifconfig wlan0 up
>
> sudo service networking restart
>
>
>  I let the setup run several days before enabling posting to Wundergound.
> My data when views on the web site locally looked fine.  When I looked at
> my data on WundergroundI discovered an anomaly with humidity.  After the
> chron task ran the humidity read low for one reading.
>
> [image: Wu_report.jpg]
>
>
> This is beyond weird. Only humidity is off and it is only the first
> reading after the network reconnect.  What could be wrong?  Have I
> discovered some really subtle bug?  If you folks think so, I can repost on
> the development forum.
>
>
> Bill - AB6OR
>
>
>
>
> --
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> 
> .
>

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