Davis WeatherLink Live: Which driver is best?

[Karen K]

Within the last days I did a some testing, and I read the threads regarding the Davis WeatherLink Live device for Davis Vantage Pro 2, and I wonder, which driver is best to use.

Let me summarize, what I found out about the drivers.

Just to avoid confusion:

• "WeatherLink IP": a discontinued adaptor to insert into the Davis console
  
• "WeatherLink Live": a separate device to receive data from a wireless Davis Vantage Pro 2 station
  

Both of them use a different protocol to communicate with the PC.

As I bought the station recently, I got the WeatherLink Live device. Then I looked for the appropriate driver, and I found a lot of them:

Vantage (weewx.drivers.vantage)

Although it is not mentioned in the documentation, I assume, that that driver is for the old, discontinued adaptors, only. I had a look at the code of the driver, and it seems so.

Could someone confirm or deny?

WLL (users.wll)

I tried that driver, and it works. There were 2 little problems.

First, I use a separate anemometer transmitter kit. Unfortunately, the driver reads the values from the transmitter kit and shows the wind, only. I changed the code a little bit, and now it reads the values from the station including the wind. I reported the changes to the author of the driver.

Second, if you stop Weewx, the driver reports an exception to the logs, but does not finish. I have to kill the process by "kill -KILL". 

Nevertheless, this is the driver I still use.

WeatherLink Live (recommended by Weewx)

That driver seems attractive, because it announces to use both the broadcast messages and the HTTP requests.

Remark for setup: Not as he documentation says, I had to set up the wind for ID 1 instead of 2 to get data.

Unfortunately, in my case, every now and then the log shows an error message, and Weewx pauses for 60 seconds. The error message reads:

Oct 31 18:39:27 LokalWiki weewx[147658] ERROR user.weatherlink_live.scheduler: Error caught in scheduler tick. Not rescheduling
Oct 31 18:39:27 LokalWiki weewx[147658] INFO weewx.engine: Main loop exiting. Shutting engine down.
Oct 31 18:39:27 LokalWiki weewx[147658] INFO weewx.engine: Shutting down StdReport thread
Oct 31 18:39:27 LokalWiki weewx[147658] CRITICAL __main__: Caught WeeWxIOError: Error while receiving or processing packets: HTTPConnectionPool(host='192.168.XX.XX', port=80): Max retries exceeded with url: /v1/real_time?duration=1500 (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7f6b45b15340>: Failed to establish a new connection: [Errno 111] Verbindungsaufbau abgelehnt'))
Oct 31 18:39:27 LokalWiki weewx[147658] CRITICAL __main__: **** Waiting 60 seconds then retrying...

As the driver uses 2 different data sources, the author may want to change the error handling and simply queries the device by HTTP request if the real time broadcast cannot be activated for some reason. I think that would make the driver more robust. 

(Remark: I don't think, the error message is really a problem of the driver but rather one of the network.)

WeatherLinkLiveJSON

I did not test this one.

Weatherlinkliveudp (recommended by Weewx)

I did not test this one, because I thought, "WeatherLink Live" will be more than that, as it uses both ways to communicate with the device.

I can be wrong but I think I read somewhere the broadcast messages and the HTML request do not deliver the same set of information. Correct me, if I am wrong.

And in one thread I read, someone decoded the V2 API of Davis, but that thread gave no further information, an I see no driver that implements that.

What would you recommend a new user to use?

[Didier Decoodt]

I'm using this one : https://github.com/Drealine/weatherlinklive-driver-weewx

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Quel temps fait-il à Auffargis ?

[Karen K]

didier....@gmail.com schrieb am Sonntag, 1. November 2020 um 11:36:36 UTC+1:

I'm using this one : https://github.com/Drealine/weatherlinklive-driver-weewx

Oh, I think, this one is not listed at https://github.com/weewx/weewx/wiki .

[Didier Decoodt]

it's a fork of https://github.com/vinceskahan/weewx-weatherlinklive-json

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[gary....@gmail.com]

Take a look at this one, it's well documented and the author is quite responsive.

https://github.com/michael-slx/weewx-weatherlink-live

This one performs well too and also has a responsive author.

https://github.com/grebleem/weewx-weatherlinkliveudp

[Karen K]

Weatherlinkliveudp

(https://github.com/grebleem/weewx-weatherlinkliveudp)

No I tested the driver "Weatherlinkliveudp". I installed and activated the driver yesterday. By now there were no problems at all. It seems, the Weatherlinkliveudp driver is more reliable in terms of rain than WLL. With this driver it is possible to stop WeeWX without the need to kill the process. 

Using the anemometer transmitter kit is possible. No special configuration is required to do so.

I have no additional sensors. So I cannot comment on restrictions there.

[Didier Decoodt]

Hi

I have tested the UDP driver (https://github.com/grebleem/weewx-weatherlinkliveudp) on a duplicate virtual machine (today I use WLLDriver from https://github.com/Drealine/weatherlinklive-driver-weewx)

You can see that the pressure has not the same value and not the same trend!

Have you an explanation?

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[Karen K]

That is really strange.

You can read the values directly out of the hardware by putting this into the browser line:

http://ip_of_your_device/v1/current_conditions
The result is a json file. Firefox for example can display it. Then look for the word "bar_sea_level". The value there is in inch HG. You can convert it to mbar and compare it to the readings WeeWX shows. Maybe, you know more then.

Generally there are two ways to read the values from the hardware. One is as shown above. The other one is to listen to the broadcast messages the device sends to port 22222. The data structure is the same. But it sends a data packet every 2.5 seconds. 

"WeatherLinkLiveUDP" listens to the broadcast messages, as the name of the driver says. What "WLLDriver" does, I do not know.

[Didier Decoodt]

I read http://192.168.1.201/v1/current_conditions and the value is correct for WLLDriver but is false for UDP driver

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[gary....@gmail.com]

I have the WeatherLinkLiveUDP driver (bugfix_october20) installed and in weewx I see identical readings with Davis Bulletin page for my PWS.

   

[Didier Decoodt]

Strange...

Could you check these values by using http://"@IP of WLL"/v1/ current_conditions

I'm using master github, I think that this is the same distribution of bugfix_october20

Le sam. 21 nov. 2020 à 02:06, gary....@gmail.com <gary....@gmail.com> a écrit :

I have the WeatherLinkLiveUDP driver (bugfix_october20) installed and in weewx I see identical readings with Davis Bulletin page for my PWS.

   

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[G Hammer]

I may do that later, but I fail to see the point.

Do you think WeeWX and Davis are both applying a conversion factor to the raw data and just happened upon the same value?

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[Didier Decoodt]

I have completely restarted my machine and now I have the same values..............

It's a mystery, but it's OK now

Sorry

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[Didier Decoodt]

Ooops, after 10 mn the 2 values have diverged (only 1 mbar)

The explanation is that weatherlinkliveudp driver uses "altimeter" and WLLDriver uses "barometer" for the station info

After change all is correct....

It was not a mystery.

[gary....@gmail.com]

Here's a handy link.

https://github.com/weewx/weewx/wiki/Barometer,-pressure,-and-altimeter

[Karen K]

didier....@gmail.com schrieb am Samstag, 21. November 2020 um 16:09:22 UTC+1:

Ooops, after 10 mn the 2 values have diverged (only 1 mbar)

The explanation is that weatherlinkliveudp driver uses "altimeter" and WLLDriver uses "barometer" for the station info

That I do not understand. Does the driver only retrieves the readings from the hardware, doesn't it? So, which way the driver can influence which values is displayed?

 

[Didier Decoodt]

No, it is not a problem of driver,

It's OK now, the 2 drivers give the same datas. 

Thank you Gary for explanations, all is clear now in my head. (meteorology is new for me...)

Have a good week-end

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[vince]

There are two pressure-related elements provided by the Davis hardware.    One is the pressure as reported by the sensor, the other is the pressure corrected to sea-level pressure based on your altitude.    The driver code defines which sensor values it uses for what generic weewx database element

Both drivers map 'bar_absolute' from the hardware to weewx 'pressure' in the database.

But...the two drivers map 'bar_sea_level' from the hardware to different elements in weewx's database.

• WLLDriver.py           puts the value into 'barometer' in weewx
  
• weatherlinkliveudp.py  puts the value into 'altimeter' in weewx

According to https://github.com/weewx/weewx/wiki/Barometer,-pressure,-and-altimeter, the correction math differs slightly, so I'd expect slight differences perhaps.  A difference of 1 mbar to me isn't something to worry too much.  You're talking 0.1 percent offset.  The sensor itself isn't that precise to begin with.

[Didier Decoodt]

Thank's a lot

I'm learning a lot of things with you

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[Karen K]

I found that additional information at https://www.manula.com/manuals/pws/davis-kb/1/en/topic/barometric-pressure-issues.

There they say, that Davis uses different calculations in different devices:

• VP2 and envoy consoles: sea-level pressure ("barometer", QFF)
• WeatherLinkLive: altimeter pressure ("altimeter", QNH)
• Vue consoles: user can choose between the two

So it seems, the author of the "weatherlinkliveudp" driver read the documentation most carefully. 

And to confuse the user or something, in the LOOP data record, Davis calls the value, what we learnt is altimeter, "bar_sea_level". 

The archive record contains all the three values barometer, altimeter, and pressure (I checked). Since the "weatherlinkliveudp" driver does not provide a value for barometer, may be, WeeWX calculates it by itself.

[flor...@pre-vost.fr]

Hi,

I'm the author of WLLDriver on Github.

Yes, I think that altimeter is the good value. But I suggest to confirm that by directly ask Davis.

Regards,

[Didier Decoodt]

thank's Florentin, I've just opened a ticket on Davis support, I will give you the result next week I hope.

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[Karen K]

To my support question to the Davis support I finally received a reply. I asked them why there are differences between console value and WeatherLinkLive value and whether that is an accuracy issue. The first answer was not helpful. So I confronted them with the statement about different calculation. They took a long time to answer. 

And from what I understand what they wrote the Davis support does not know for sure. Who then?

This was their answer:

Hello, 

That looks like it is the case. They are calculated different. 

To tell you the truth I was not aware of this. 

* * * 

Tom Raymond 

Technical Support Davis Instruments

[didier....@gmail.com]

The right value is "altimeter"

See specs https://www.davisinstruments.com/product_documents/weather/spec_sheets/6100_WL-Live_Spec_Sheet.pdf