The climate (in the shed) is different from what I expected: humidity is (so far) within limits of what the current PC (a Dell optiplex GX270) can handle. I expected humidity to become a problem before temperature. Temperatures are at the moment dropping below 'operating range' and a couple of cold days are coming up here in the Netherlands.You can view the results at the weather station page but remember this is in the shed. Real measurements done with (something resembling) meteorological standards will be later.
But these measurements have learned me a few things and helped with a few decisions for the project sundial weather station:
The flickr picture is also some experimenting with the gimp.
- The humidity in the shed is not much of a problem.
- The temperature might be, but if a really low-power PC in an IP66 housing can survive an outdoor climate, it should survive in the shed.
- The conrad temperature sensor is not very precise in outdoor temperatures. So the 'outdoor' temperature / humidity will be measured using 1-wire sensors hooked up to the future weather station computer. The Netley Marsh 1 wire weather station has nice ideas and pictures how this can be done and a small 'sensor house' like the one they use would fit better in our back garden than a full-size Stevenson Screen (the official name of the white 'meteorological hut' which tries to shield thermometer and hygrometer from local influences).
I wanted to install an extra package on the wardriving box but found out that the choice of distribution: Debian etch is not available anymore, not even as 'oldstable'. A bit of searching finds that I need to look in the Debian distribution archives.
I'm not sure whether I'll keep using Debian versions for the wardrive-box. I want something nice and small and manageable, and the option for a custom kernel (no initrd, preferably no udev).The interesting bit is that I built the wardriving box in January - February 2008 and it basically ran regularly since that time without software problems.
The extra package I wanted to try is lm_sensors, for the other project: Sundial. I was wondering how high/low the system temperature would get, and whether it would stay within the 0 - 50 ⁰C range. An IP55 rated case might be a good idea for use in the garden shed (which is semi-outdoors). The question is will the mainboard stay above 0 ⁰C when it is -15 ⁰C outside. I know from the wardriving box the Alix board generates some heat, but is it enough to keep itself warm.The Alix.1c/1d have a temperature sensor, according to Getting started with voyage linux it should work with the w83627hf driver which indeed loads and gives a readout.
I came across the alix.1 series hardware while looking for something low-power for project sundial. Later calculations showed the 'powered by the sun or wind' part of that project would be too expensive compared to just using a plug.
Update: The archived etch works, but lm-sensors wants perl, which is not part of the stripped down debian on the wardrive box. For as far as I can see that is because there is one perl script included. Time to rebuild from source with that script removed.Update 2010-08-03: Looking where you are going helps too: Voyage Linux is Debian-based but optimized for embedded apps. With debootstrap under Ubuntu or Debian I could set up a newer development environment for the wardrive box and test Voyage Linux.
I looked at the project sundial power calculations again and did some more calculations: even when I take the parts with the lowest energy usage and get the average usage down to 5.4 Watt, the investment in solar panels to get even through December and January in the Netherlands would mean it would take somewhat over a 100 years to 'earn back' the investment in the solar panels. So maybe it is a better idea to power the weatherstation from the grid and make sure the earth connection is really good to avoid damage to the power grid at home should lightning strike it. Still using wifi for data transfer would be a wise idea.
Update: About the same goes for wind power: because we live in the city and can't put up a 10 meter high pole for a wind generator the generator would become quite expensive.
Anybody know any leads in receiving data from a weather station which uses "instant transmission" on 868 MHz? I'd like to receive data from such a weather station. In linux, on the server. Some device which would receive the data and present it via a serial port would be great.
Update: the wonderful thing about standards.. I learned that there is no standard for data from weather stations on 868 MHz and that a sensor from brand A will not be received by a receiver from brand B. Time to be more specific: the weather station is a TFA-Dostmann "Stratos". I already e-mailed a technical contact at TFA-Dostmann about this.
Update 2010-01-14: Answer from TFA-Dostmann: it is impossible to receive the data from that weather station on a computer.
Pouring rain this morning... the most interesting weather sensor at home would be a rain sensor, which is planned in the self-powering weather station.
Finally I counted a few light pulses with the one-wire counter. No big circuit with the Velleman MK120R kit but just a photodiode and a resistor hooked up to the counter module. I got the idea from looking at the schematics for the Hobby Boards 1-Wire Lightning Detector. The counting circuit is a phototransistor (in an optocoupler) and a resistor. With a bit of tweaking on the resistor I eventually got the counting circuit to count 2 light flashes from a flashlight. With some more tweaking of the resistor value I think I could count red flashes from the electricity meter.
I also installed the lightning detector under the roof. But it is too close to the wiring of the house I think: sofar all counts are related to me being in the attic and turning on the light. In a 'real' setup I think it needs to be away from the house. Something to keep in mind for the project sundial weather station.
Another instance of me thinking so seriously about a project that I started a webpage about what I want to do and how and collecting the knowledge and ideas that I already have: building a wardriving box. I first thought of a small PC for project sundial, the self-powered weather station and gps time receiver but I got the idea that this could also make a really nice Wardriving box which would do just that.
I dug up the Conrad weatherstation I'm planning to use as weatherstation in project sundial. I updated the page with information about the order-numbers of the different parts (no longer available from Conrad). So far, most sensors seem ok (although I'm not sure everything is calibrated) but the rain sensor gives absolutely no usable readouts and gives weird numbers for the calibration procedure. The wind speed sensor is a simple revolution counter which will need some software work to convert to average wind speed and wind gusts.
A company in the US, Solis Energy, is producing solar-panel power systems especially geared towards running wireless networking in hard-to-reach places. Sounds like a turn-key version of some of the functionality in my project sundial for a self-powered weather station. Sources: Computerworld Australia: Power Wi-Fi using the sun, says startup Slashdot: Solar Powered Wifi.
I've been thinking about building a weather-station / ntp server with solar power for a while, and decided to start documenting the design, the ideas and the (lack of) progress. Named project sundial because it uses the sun to tell time, just in a somewhat convoluted way.