A while ago I bought one of the Maplins weather stations, just for fun really no plans with it. The device came with a pole to which several sensors could be attached: temperature, humitidy, wind speed, wind direction and rain level. The other important bit in the box was the control station, which is a large LCD screen based output for the information which is gathered in the sensors, it also gives an attempt at forecasting. Areas of the screen are pressure sensitive which allows for a touchscreen style interface for changing views etc.
All pretty cool, and looks great on the worktop displaying weather info. But the geek inside of me wants more!!! Along with the aforementioned components comes a USB cable and a cdrom, the brains also does data collection which can be extracted using the software on the CD.
Thats also cool, but unfortunately no software for Linux included on the disk, not to worry pywws from Jim Easterbrook steps in here. I won’t go into detail on how I set this up as there is a good tutorial here: http://www.weather.dragontail.co.uk/index.php?page=station_setup but what it gives you is a way to extract the weather data from the brains of the weather station store it on a pc then display it through a pretty web interface. Gives allsorts of graphs and fancy data tables.
This was quite cool, but got me thinking about what to do with this data, can it be uploaded to some weather data aggregation service for the greater good? Thats where I found weather underground, or wunderground, and their API. Since finding it I’ve been using it to both upload my data and also retrieve data for various projects (nagios monitoring, temperature monitoring). Pywws contains the ability to post the data to wunderground built in. Great, I have a nice solution the head unit connected via usb to a server in my garage. I can’t see the unit, but I can see the data via Pywws.
It was all going well, that is until the batteries in the head unit run out and the project headed back onto the todo pile. That was until I was working on a seperate project where I was trying to retrieve the RF signal on 433mHz home plugs and saw some random traffic. After thinking it must be a neighbour or a cars remote locking, i realised the data was being sent on a regular basis. It eventually dawned on me after a bit of googling that the data may be from the sensors on the weather station as the batteries were still active on that side. A small amount of googling later and I found that I was able to not only retrieve that data but also decode it into readable data.
To explain, I am using an RTL DVB dongle which is popular in Software Defined radio circles as its frequency can be set to pretty much anything. I haven’t delved into the SDR side of things, but I’ve been using it to scan 433 and 868 mHz frequencies to try retrieve data on RF control devices within my home. Using the dongle and the RTL-SDR software http://sdr.osmocom.org/trac/wiki/rtl-sdr I can achieve this.
My aforementioned googling around the weather station data led me back to a project I was already using, OOK-Decoder, OOK being the form of modulation used in many RF devices and seemingly the weather station. The OOK-Decoder project also comes with another executable wh1080, which it turns out is my weather station.
The project was written by a chap who has a remote weather station, so he was sending the data over a multicast network, recieving it locally and then decoding it. This means its a bit overkill for what i’m achieving but I’m achieving it. Essentially, there is a machine which sits within the vicinity of the weather station sensors with the DVB dongle attached and running OOKD which takes tunes to the 433mHz frequency by default, and streams the raw data over the network. On the receiving (network) end, a PC runs OOKDUMP to output the stream of OOK data raw or runs the wh1080 binary which takes the stream of OOK data and output a json formatted text file.
Why it’s overkill for me is that I run both ookd and wh1080 on the same box, I’ll probably figure out combining the two at some point to reduce the load but for now it works.
The next step is to do something useful with that data, so I wrote a fairly rough python script to upload the data to Wunderground. I’ve also made the wh1080 output the file to a directory which is accessible via a webserver to make it useful to any scripts I write for other projects. Having the data stream directly to the server now also means I can relocate the previously USB tied control station back into the house, double win!
So in a nutshell the process to get weather data directly from a Maplin weather station:
- Install rtl-sdr as per: http://sdr.osmocom.org/trac/wiki/rtl-sdr (dont forget to blacklist the dvb driver)
- install ook-decode as per: https://github.com/jimstudt/ook-decoder
- Run ookd and wh1080 (don’t forget to run with & at the end to allow access back to the console), this outputs to /tmp/current-weather.json by default
- Create a weatherunderground account http://www.wunderground.com/ and create a personal weather station ID
- Use my python script with the ID generated above and password to upload the data
Maplin weather station
Jim Easterbrooks PyWws
Jim Studt ook-decoder (and wh1080)
My script to publish json data to wunderground