Weather Whimisicality

I got Lisa a Davis Vantage Pro Weather station for Mother’s day. I got it happily mounted on the roof and then the fun started. I found some perl scripts on the net to put the data into MySQL and onto a page. Joe Eaton has a really nice site.

Then the fun started: It turned out that Davis had upgraded the firmware. It now calculates the trend in barometric pressure, and of course the status message has been modified to include that data. Unfortunately they neglected to tell their own tech support, which was still shipping the spec for the old rev. Then, in the middle of chasing this down, the barometer and indoor hygrometer on the station broke, and I had to get a new one from Davis. Since the changes I had to make in the scripts involved the barometer, I took a week off.

In that week I put both bunter and chuck onto a UPS. It’s already gotten us through half a dozen power flickers. Life is good.

I also played with the windows software that came with the Davis serial interface. There’s less there than meets the eye. No database connectivity (text file export only), a tolerable looking ftp to website capability, and way to send your data to the Citizen Weather Observer Program. More about that later. It didn’t go through our firewall (as it shouldn’t) and there was no information on what I needed to do. Based on other info it’s telnetting to port 23, but opening port 23 wasn’t enough to make it work.

When the new box got here, it was fairly simple to hack the appropriate script to handle the new message. I got it making a simple page every 10 minutes, and then instead of getting the database up, decided to jump on another old idea, and get a webcam going.

We all have old 3com HomeConnect webcams. Nice beasts actually and available now from somebody else. No manufacturer Linux support of course. It’s even supported in Video for Linux. Almost. It’s one sensitive critter (great in indoor light) and the (software) AGC isn’t supported in Linux. And won’t be, because TPTB don’t want signal processing in kernel space. Which makes sense, but leaves me with a camera that whites out when pointed into daylight. The AGC code is posted in the forum on SourceForge, but I’m not Linux jock enough to know if I have to recompile the whole kernel to make it work or if I can just compile the driver once and have it work at least with all future 2.4 kernels. (I have a day job. I use the binary updates from RedHat. I don’t have 4 or 5 hours a week to keep up with compiling even just the security fixes) I left a question on SourceForge, and decided to try the Windows drivers.

Under Windows the AGC is used. When I point the cam out the window I can watch the white out turn to a pale washed out image. Not good enough by far. Well, that made me lose interest in using that cam, since I doubt the AGC under linux would be much better. Maybe someday I’ll try further.

OK next idea. We have an old Epson PhotoPC camera (circa 1996). A little googling and it’s off to SourceForge for the eponymously named “photpc” a handy command line control program for the PhotoPC and a bunch of other cams that use the same chipset. Compile, read the man page, shell script called from cron. It’s running. All right!

Now to Staples for three 6 foot serial cables, string them together, ductape the camera into the window, it works. You can see the results at I’ve got it using the last picture before sunset all night, but at least on cloudy days even that picture is black. I want to have a sunny evening before I decide how close to sunset I can actually take the last picture.

And now back to the CWOP thing. Can you say no docs? I knew you could. There’s windows and mac software, but it’s all closed source binary only, and mostly won’t also feed a website or a database. (Davis Weatherlink will feed a website, but then you have to screenscrape to get into a database). It’s all kludged on top of ham packet radio. (They did it first, then they started relaying over the internet, then NOAA invited non hams to join) All fine and good, but after hours chasing things down, I have the APRS spec, references to something called AX.25 (I can guess), and a couple different servers to telnet my APRS packet to. (on port 23). No source code.

Fortunately, a lot of work went into the APRS spec. Hams are all geeks. I guess the idea is that with a spec that good, any geek worth talking to should be able to make it work. I’ve downloaded the spec, and it looks like about 16 hours work to be asking questions cogent enough to get them answered. There is a defined APRS weather message. Do you think that CWOP uses it unmodified? Do you believe in the Easter Bunny?

We’d really like to get this going. Besides being great geek fun, the climate maps for this area are way wrong, and maybe if we feed them data for a few years the 2010 versions will be better.

However, I’d also like to get the information into MySQL, and sendmail is being naughty again. So we shall see.

2 thoughts on “Weather Whimisicality”

  1. Check out my “about” page. I have written, in perl, a couple of scripts to pull data from the Davis VP, log to a MySQL DB, and upload to I’ve also written a graphing module using phplot in, of course, php.



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