Saturday, May 30, 2009

Daylight measurements

The next project, now that the door bell growls in the mac and the power orb is orbing like mad, is to make a small weather station, with a wind speed meter and a daylight meter in order to control the sun shade in the kitchen.

In the late afternoon the kitchen gets a lot of direct sun, and while that is a good thing in the winter months, it is not as nice in the summer, as it makes it very hot and the refrigerator has to work overtime.

I have an electric sun shade, of the extending type, which is connected to an ELV device making it controllable from the server. However, I cannot lower it automatically, since if it is raining or windy or simply cloudy, it is not a very wise thing to do. I do raise it automatically every day at 20:30, which should cover it most of the year, and in case I need to go out of the house and don't come back till late while the shades are off.

So I started the weather station by getting an LDR and connecting it to the arduino. Using the standalone temperature logger I made a few months back I could leave the arduino in the kitchen the whole day logging the amount of light.

The results are great I think! with the steep rise around 14:00 which is when the sun comes around the bend, and a clear difference between the times when the sun shines and when it doesn't. I think a threshold at around 800 will do the trick.
Furthermore I am quite happy with the excursion of the sensor, going from 0 to 916 at least, which is a 89% coverage of the 5V conversion range!
Now, off to the wind speed! Already spent the night disassembling an old VCR, and got some promising parts out of there!

One more note. I thought a lot about how to make a rain sensor. Not necessarily measuring it, but just to detect if it is raining or not, but concluded that if it is rainy, the sky will be overcast, so it won't be necessary to lower the shades!

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