Has anyone done a remote, solar powered weewx system through a cellular modem?

[Thomas Keffer]

Hello, all.

Our local Nordic ski club, Tea Cup Nordic, would like to install a weather station at their hut. The site has no power, is fairly remote (in Mt. Hood National Forest), with barely adequate cellular service.

We're aware of the Davis's "Vantage Connect" device, which would probably fit the bill, but it's very limited in what it can do. We were thinking more along the line of a low-powered PC (maybe a RPi), hooked to a solar-powered cellular relay. 

Has anyone done anything like this? Any tips / hints you can give us?

Thanks in advance!

-tk

[Per Edström]

I use Ericsson W25 mobile router (http://www.fixedwirelessterminal.com/ericsson_w25/index.html) but I guess it uses too much power for a solar-powered station. It does however have external antenna for GSM/3G so with a yagi-antenna the reception/speed is greatly improved (also to select a specific basestation to receive from if multiple around). The advantage with this router is that is can emulate PSTN or "old" fixed phones. My alarm requires to dial over a fixed line so this router does the trick but using a mobile SIM-card..

Will a USB-modem work or is the signal too weak?

[Per Edström]

Also, the W25 does have a Debian CLI-interface and USB-port for flash drive so it's possible to write scripts in it to i.e. save camera images and then send to a web page or just FTP to a server. All settings in the router can therefore be changed over SSH. Quite useful!

[Per Edström]

I guess this will make a low-power solution with R.Pi:

http://prx.sytes.net/PI-GSM.pdf

[tds]

Regarding the data link, does the site have line-of-sight to a not-so-remote location that has better internet access?  If so, you may want to consider setting up a direct wireless link using some of the products from ubnt.com.  I live on a mountain and our internet is provided by a small company that uses the airMAX line from Ubiquiti.  Their repeater is run off battery backed solar power.

[mwall]

On Friday, November 8, 2013 2:44:41 PM UTC-5, tds wrote:

Regarding the data link, does the site have line-of-sight to a not-so-remote location that has better internet access?  If so, you may want to consider setting up a direct wireless link using some of the products from ubnt.com.  I live on a mountain and our internet is provided by a small company that uses the airMAX line from Ubiquiti.  Their repeater is run off battery backed solar power.

i'll second the ubnt reference.  we run a link from island to shore over a mile of water and a quarter mile of thick spruce treetops using ubnt hardware - the low end pico stations attached to parabolic antennas.  the link easily maintains over 50 Mbps even in thick fog.  i'm not sure what the power budget is, but the reliability is awesome.

m

[Dawning Sky]

Our wireless internet links are actually over >10 miles and they work
very well. And they don't use that much power. For example, the more
powerful PowerBridgeM has a max power consumption of 8W and a 2.4GHz
NanoBridgeM is 5.5W. I think the power budget for most cellular
modems are similar. The RPi itself consumes ~5W max.

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[Thomas Keffer]

Thanks everyone, for the great suggestions! Keep them coming!

It seems like there are two general approaches to this problem. 

1. Put the processing power at the remote site, then continue as usual with weewx. It would be no different than what I have in my home, except the link is through a cellular modem (instead of broadband DSL); or
   
2. Put the processing power at a local site and use the cellular modem solely as a tunnel to the instrument.

Personally, I had assumed that in a low-power, high-maintenance site like this one, approach #2 made more sense, but it seems like a lot of you are actually deploying RPis at some pretty remote sites. Is that true? 

What are the pros and cons of the two approaches?

-tk

[vds]

Wow - that Vantage Connect is expensive but it does seem to simplify the sysadmin side, assuming the cellular works there ok.  Some links are 

• http://www.wxforum.net/index.php?topic=19966.0
• http://www.agprofessional.com/special-sections/product-news/Davis-Instruments-has-breakthrough-in-remote-weather-monitoring-227852921.html
  

Perhaps ask on the hardcode weather zealot forums like wxforum.net ?  I have to think lots of folks have tried to cook up a really-remote weather site.

If you roll your own solution, I'd guess the probllem is how much power can you generate vs. how much do you need. One solar powered Pi setup is documented at http://reviews.cnet.co.uk/desktops/how-to-make-a-raspberry-pi-solar-powered-ftp-server-50009923/ - the fellow in GB builds solar+battery setups for folks so maybe he'd be a good resource to ask.

Personally given no power at the site, I'd worry about the environmental part of things, would a real computer (so to speak) fail due to being cold/damp/etc.  Maybe throwing the money at the Davis sensor/transmitter would be your least blood pressure option (?)

[Per Edström]

If we (weewx) could implement the function to read the WMR200 internal data logger and from that update the Weewx DB, then one solution could be to power up i.e. an R.Pi, have it connect to Internet over cellular modem and update the Weewx database from the WMR200 stored data. Then when all pages are generated and uploaded, do a controlled cellular disconnect and a shutdown of R.pi and have a timer cut the power to everything ( I guess R.Pi doesn't have a sleep mode?) but the WMR200 (that will continue to log data). The "uptime" will be only 15-30 minutes at the most but the timer will have to have margins so that all activity have time to finish and shutdown.

After say 6, 12 or even 24 hours the 12V-timer (or what the solar panel is providing) will power up R.Pi again and repeat the process. This will save quite a lot of power (if one gets all scripts to work that is.. ;-) )

[george hofmann]

I thought about doing this. We bought some property near Lake Chelan (WA) for the purpose of growing some grapes. We live 200 miles away. I put a Davis weather station on the property to gather growing degree day and frost data. But I have to appear on the site every 55 days or less with my aging Windows XP laptop to download the data. I have power to the site but not Internet. Plus if the system goes down I may not find out about it for a long time.

To solve this problem I thought about using my old TMobile Exhibit phone as an Internet interface for Weewx. As a phone, this unit is a POC due to inadequate memory, a slow processor and bloatware. But you can configure it to be a wifi or tethered hot spot and still use TMobile's data service without paying extra. They have a $30/month pay as you go plan that allows unlimited data. So that would probably work for you, assuming there is a TMobile tower within range. I imagine you could run the local machine as a web server rather than FTPing the files out. That would limit the amount of transmitting that the cell phone would need to do thus cutting the power requirement.

As it turned out I decided to install a Weewx server and feed data to the Ham radio APRS system, since I already have those parts lying around. I can thus monitor the health of the system remotely, see recent WX data and download the data to my new cell phone at my convenience when I am at the site.

George Hofmann
Edgewood, WA