959 Radio
Weather Station
A home constructed unit was the intention but a certain snag was unable (see below) to be overcome so I purchased a Lacrosse WS2350. This unit has wind speed and direction, indoor and outdoor humidity and temperature, pressure and rain gauge. Most importantly the data could be downloaded via a RS232 interface. For those interested in writing their own code to interrogate the unit there is a whole suite of C libraries written by Kenneth Lavrsen on his Open2300 website.
I wanted to use ‘Weather Display Live’ on my website and experimented with various attempts using the above libraries to generate the files required by WDL with only partial success. The constraints were that I didn’t want to run a desktop PC 24/7. In the end it was easier to use ‘Weather Display’ to interrogate the ws2350 and use it to send the files to WDL since these two programs work seamlessly together although I found the set up not very intuitive. I got around the 24/7 problem by using a modified thin client whose power requirements were low.
On Ebay I purchased an HP5720 thin client, this has a 1GHz processor and 512Mb of RAM and runs XP embedded from a 64MB flash card. The flash card sits on a standard 44 pin IDE connector so can easily be replaced by a standard lap top hard drive which can be just about shoe horned into the cabinet. I used nLite to cut down my spare Windows XP which has been looking for a home since my Windows 7 upgrade. With nLite you can cut down XP to just a basic operating system with only the applications you need. Since the thin client doesn’t have a CD drive you have to boot from a flash device. USB Multiboot does this job very well. Once you have XP installed with only the needed apps and services running you can connect to your home network, map drives and install software. A registered version of WD is reasonably priced and runs well on the thin client using the RS232 interface. It will automatically send data to your website for WDL and you can also request it to make a text file of any of the data it holds including archived data. I wrote a small batch file to send this data out of one of the thin clients’ USB ports to a PIC driven unit with two 20x 4 LCD displays which is on the workshop wall to display current weather data. This is also relayed wirelessly to the Lounge where another 21 x 7 display shows current weather.
How to setup Weather Display and Weather Display Live
Link to Indoor Units
The homebuilt weather station worked well up to a point. An HP05 (Elektor shop) digital pressure sensor provided atmospheric pressure and indoor temperature. This unit was intended for indoor use as the atmospheric pressure inside your house is the same as outside (if it isn’t you should see someone about it). The outdoor sensor was an SHT71 (Farnell) which provided outdoor temperature and humidity and hence dewpoint and heat index. The problem came with wind speed measurement. I didn’t feel able to construct a vane type that would survive the weather. The data format from commercial weather station spare ones was proprietry. I decided to to attempt an ultrasonic wind speed measurement. Two sensors one meter apart aligned north/south. Ping one direction then the other, difference in time can calculate wind speed. Same for east/west. Simple math can give wind speed and direction. Problem was it was inaccurate, when the 40KHz ping is received the resonant circuit builds up to full output and at some point a schmidt triiger has to decide on triggering to stop the timer. This may be pulse n or n+1 depending on temperature, day of the week, who is in government, any number of things. The difference in time between pulses is equivalent to about 3 mph, an unacceptable error.Commercial units of this type must use 250KHz sensors which are very expensive instead of the standard 40KHz jobs. This project may get revisited later after further thoughts. Colleagues said why invent the wheel. Well that’s what hobbies are about and sometimes you can make a better wheel.