Personal Weather Station using BifferBoard

I have managed to re-compile openWRT to run on the bifferboard, and include python, libusb and pyusb in the main root directory.   I also included the wget utility, because I thought it would come in useful, plus a few other potential future extensions (lighttpd web server and wireless LAN support).
This fits on the bifferboard onboard flash memory, with about 1MB to spare.

I created a /home/weather directory and extracted a recent pywws tar archive into it.   I was very pleased that running TestWeatherStation.py produced a table of numbers as expected, so it looks as though the bifferboard is talking to the weather station ok.
Here it is:

Set up the initial weather database by doing

cd /home/weather 

python pywws/pywws/LogData.py -vvv /home/weather/data

This creates /home/weather/data/weather.ini and a directory /home/weather/data/raw which contains the raw data.

Run Hourly.py for the first time to process the data, and set up the weather.ini file ready for customisation:

pywws/Hourly.py /home/weather/data

Customise /home/weather/data/weather.ini to do what you want it to do - in my case update weatherunderground....

All is looking promising here - seems to send the update ok on an hourly basis.  There are two problems though:

• There is not much disk space left now I have added all of January's weather data (256kB ish)
• I am concerned that I will wreck the flash chip on the bifferboard with all this writing.

One option is to store the weather data in a ram disk and just accept that after a power-off it will need to re-initialise itself - not sure how pywws will cope with this - I will need to load some default weather.ini file from flash every time it boots, then let it update itself as best it can.

As a quick alternative I have found an old 256MB SD card and created an ext3 filesystem on it.  This detects as /dev/sda1 when plugged into the bifferboard.   I have modified /etc/rc.local to mount this as /home/weather.  This should solve my full filesystem problems.  [Note:  I used an ext3 filesystem because my openWRT build could not detect ext2 - this was a bit of a surprise because I thought you got ext2 support free with every Linux kernel...].
Then it is just a matter of a cron job to do the hourly updates - crontab -e, then add:

13 * * * *       python /home/weather/pywws/Hourly.py -v /home/weather/data >> /home/weather/Hourly.log 2>&1

If it works, you should continue to see the weather in our back garden at: http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=IHARTLEP2.

Mistake 1:  If you put an SD card into the dual USB bifferboard, it disables one of the USB ports.  This is bad if it was the one the weather station was connected to....

Mistake 2:  Believe people when they say the clock on a board is no good.  The Bifferboard clock is no good.  Not only does it loose its time when powered off, but it drifts - by a few minutes an hour.  This meant that pywws got confused about when it should update weatherunderground, because it thought time had suddenly gone back to 2009....   To avoid this I compiled ntpclient as a package and downloaded it onto the bifferboard.   I now have it set to be called once on boot, then every 10 minutes by a cron job.  This should keep it somewhere close - just hope the time server owner doesn't mind - If I get a complaint I will have to set up my own time server...

Building openWRT for BifferBoard

I had a go at building openWRT for my new bifferboard computer last weekend, but had trouble with it - it looked like the kernel started, but then panicked around the time it was supposed to be starting init. I suspect it was something to do with the j2ffs file system.

I decided to try to be clever and rather than fix openWRT, start from scratch with an OpenEmbedded based build. I think this was too big a step - the main problem was that OpenEmbedded failed to build because some sources from handhelds.org are not available, so I had to learn how to alter 'recipes' to build them from sources from another location. I got ipkg-utils to build this way, but then hit more trouble with openssh. I decided it was going to take me a long time, so went back to openWRT for now to try to get something working!

This time I followed the exact instructions from the bifferboard site, including downloading the specific revision of openWRT.   This all compiled nicely without any errors, so the next challenge was to get it onto the board.

Flashing over the serial line seemed to take a very long time, so I had a go with network setup.
I downloaded the bifferboard utilities using:

svn co https://bifferboard.svn.sourceforge.net/svnroot/bifferboard

This provides a simple python based tftp server.   I had to modify it to use a fixed ip address for my host computer, because the script assumes that you are using eth0 for the network interface, and I was using wireless.
You then need to make sure that there is a file called bzImage in your working directory and start bootp_server.py - I had to do it as root because I got some permission denied errors about opening sockets, and the easiest way to fix it was to be root - there is probably a more elegant solution though.

First I created a symbolic link to the bzImage file that openWRT had produced.   Then booted the bifferboard with the serial line connected and pressed ESC to stop the boot process.   Entering the tftpflash command downloaded the bzImage from the server and flashed it to the disk - much quicker than a serial line.
The kernel started, but failed with a lot of j2ffs errors - I think this is because I had my old root filesystem in the flash memory.
For the next attempt I created a symbolic link from openwrt-rdc-jffs2-64k-bifferboard.img to bzImage.
Re-flashed it again the same way and it boots!

A minor detail was that I could not log into it - the serial console was fine and both telnetd and dropbear (the SSH server) were running, but I got 'connection refused' when I tried to connect.   It turned out that there was something called 'firewall' running.   I deleted /etc/rc.d/S45firewall and re-booted and it worked properly - I could telnet in initially without a password, set a root password, then use ssh to connect.
Success - Now I just need to sort out the weather station software to run on it - back to the cross compiler....

running make package/symlinks in the openWRT directory adds all of the available packages to the openWRT menuconfig program.
Added the ones I know I need (libusb, python, pyusb), plus a few others that might come in useful later (atheros wireless card drivers).  Then make.....and wait...