Weather Station Data

The weather station used is a Gadget N96GY sold by Maplins. This is a generic 'fine offset' station sold by numerous companies. It consists of an indoor base unit and 3 outdoor sensor units. The base unit connects to the thermo/hydro unit using a 433MHz wireless link. Both units are battery powered. There is no alternative mains supply for the base unit.The windvane and rain sensor are powered from the thermo/hygro module wia a connecting cable.

Base Unit

The Base unit receives and displays the readings sent by the outside temperature, humidity, wind and rain units. This happens every 48 seconds. The Base unit also records the indoor temperature and humidity. Although readings are received and displayed every 48 seconds they are not stored in memory this often. The base unit can store up to 4080 sets of data. With the recording interval set to 10 minutes this allows the unit to store at least 28 days of data before it needs to be downloaded to my laptop. In practice the weatherstation is always connected so the data buffer just works as an emergency store, just in case something happens when I'm not around.

Timekeeping for the base unit is controlled by it's own internal clock. There is no radio controlled timekeeping although I understand there is another model of this type that does have this feature. Personally I am glad it doesn't have this 'feature' as it has caused me no end of trouble with the old lacrosse unit. The base unit allows the setting of alarm values for all readings and for a storm warning. As well as displaying the data from the sensors it calculates dew point and wind chill values and stores max and min values since last reset. It also measures and displays relative and absolute pressure and rainfall over the last 1 hour and 24 hours. Connection to a PC is via a supplied USB cable.

Wind vane & anemometer

The wind vane registers one of 16 possible compass directions and is free to rotate through 360 degrees. The anemometer is a conventional cup style. Both units are connected via a 2 way telephone style cable to the temperature module. These units cannot work wirelessly. Internally they just consist of magnetic reed switches,one in the anemometer and 16 in the windvane, activated by magnets attached to the moving parts. Each switch in the windvane has a resistor attached o it so that a different resistance value is presented to the thermo/hygro unit depending on which way it is pointing. I expect this would make it impossible to extend the cable if needed as it would mess up the resistance values.

They are mounted on a 3 metre pole fixed to the side of my garage roof. Overall it is about 16ft high. This is insufficient to get it above the turbulent air created by surrounding objects. We are also surrounded by mountains which funnel the wind into different directions from the general flow so readings can only be taken as a guide to the general direction. So far, despite severe wobbling, it as survived the welsh weather. The highest recorded gust so far has been 68.2mph


Rain sensor


The rain sensor consists of a funnel that collects the water and directs it to a pair of buckets arranged like scales. As one bucket fills it tips over the scales allowing the second bucket to fill before it tips back again. Each tip is registered by a magnet activated reed switch. Each tip corresponds to 0.518mm or 1/200th of an inch of rain. The unit is connected via a 4 way telephone style cable to the temperature module. This cable provides power to the rain sensor from the temperature module and allows data transmission from the rain sensor back to the temperature module. The rain sensor cannot work wirelessly.Readings are relayed to the base unit about every 2 minutes.


Temperature and humidity sensor


The temperature and humidity module measures the outside temperature and humidity of the surrounding air. It's placement is critical to accurate recording. It must not see any direct sunlight but must also have free air movement around it. The module acts as the hub for the other sensors and is the only unit that connects to the base unit. This can be with a 4 way telephone type cable or wirelessly.


Computer

Initially, the weather station was linked to my 'everyday' desktop computer. This is a 2.8Ghz P4 running Windows XP. Amazingly, the Heavy Weather software consumes nearly 30% of the CPU's resources when running. The PC uses about 100W of electricity when in 'standby' mode, i.e. with the monitor off and the drives stopped. I had a hunt around for a cheap laptop to dedicate to the weatherstation and found a Dell Latitude CPi going cheap. This only has a 400Mhz PII processor, 128Mb of memory and a 6Gb hard disk running XP. It takes a full 5 minutes to boot up and load all the software, but once running copes with Heavy Weather and Dorgem (webcam software) OK although it sometimes doesn't find the webcam USB port when booting. It only consumes 9-10Watts and has the advantage of battery backup in case of power cuts, which are not uncommon up here.

In October 2008 I updated the laptop to another Dell, this time a C610. This has a 1GHz Pentium III processor, 256 Mb of memory and a 12Gb hard disk and runs Windows XP again. As of January 2009 I am leaving this laptop running 24hrs a day.



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