The Computer

Weather data is received from the station by a Davis wireless Weather Envoy which is connected via USB to a trusty old dual 1.5Ghz Pentium III PC. Based on the Intel 440BX chipset, the Asus P2B-DS motherboard has proved itself as a reliable and remarkably stable workhorse. Although dating from 1998, these boards still have a loyal following with various modifications available to enable it to run CPUs (like the PIII) that didn't exist in 1998 at impressive speeds that weren't enabled by the manufacturer. As well as processing all the weather information in the background (most relevant applications run as services), the PC is used for day-to-day applications like accounting, writing documents, photography and web design. So far, it has proved more than capable of all these tasks. It has run 24/7 for over 2 years and it's predecessor did so for over 5 years before that.

Hot tempered?

Probably the only problem with running new and improved CPUs is the heat they generate. Running the PIIIs saw CPU temps over 60 degrees C on some summer days. The general solution is to put bigger heatsinks and/or fans on the chips to keep things cool, but that tends to make for more noise. When the PC lives in the house and you have to sit next to it to work, then the extra racket isn't really appreciated. The option here was to use two Silverstone heat pipe CPU coolers which conduct the heat up to the enormous copper heatsinks - much larger than what would fit on top of the CPUs. Nothing was manufactured for the slot 1 / Socket 370 arrangement in the P2B, so a Socket 478 (P4) unit was adapted. This involved carefully hacking off the aluminium mounting lugs and fabricating some spring clips to hook it onto the S370 lugs. I also had to bend the heat pipes to allow the two units to sit side-by-side.

A  thermaltake Smartfan II 80mm replaced the case fan at the end of the cardboard 'duct' to further reduce noise in cooler weather. The duct acts to draw air through the heatsinks without giving them their own (noisy) fan. Cooling is further aided in summer by drawing cool air from under the house through a hollow plinth I knocked together from scrap timber.

Connectivity

Due to our relative isolation, the Salisbury Plains weather pages come to you via a 128k ISDN connection. While this is a vast improvement on the old dialup service, it is a far cry from the ADSL connections enjoyed by our counterparts in the larger towns. However, it cannot be beaten in terms of reliability and uptime. In order to share this single connection with the various computers and equipment around the farm, a Cisco 803 router has been employed to take over from the carrier-supplied NT1+2 ISDN terminator/modem unit. This also increases reliability - something the NT is not renowned for, particularly when constantly uploading data as we do.

Long-distance links

One of the issues in distributing a network around a farm is the distances involved. It is obviously impractical to run cat5 cable over the hundreds of meters between buildings, so wireless links were the obvious answer. There are a few commercial options available, but it was cheaper (and much more fun) to develop a home-built system. With the advice of Rob Clark from Freenet Antennas, some inexpensive hardware was installed in conjunction with some scrounged antenna dishes and our own fabrications. The result has been running since 2004 without a hitch. Take a look here for pictures and some more details, including a neat 12volt UPS system.

Power Supply

Another consequence of living in the bush is that the mains power can be a little unreliable at times. To minimise the impact of this, all our hardware runs on some form of UPS. The largest of these is the APC SmartUPS 2200XL. This massive 2.2KVA unit is probably overkill for the gear it operates, but it was going cheap so we couldn't resist. With the two external battery packs plugged in, the UPS can keep the server and a PC running for over 8 hours.