Very interesting - I was thinking about using an Arduino, but the ease of setting up and programming the Pi (and the fact that it goes for $35) has completely sold me on it. I'm usually more of a C++ guy as far as programming goes (software engineer by trade), but being able to quickly whip something like this up in Python and take advantage of its facilities to easily wrangle data from text has some real perks.
For plotting, I use MatPlotLib (
matplotlib: python plotting — Matplotlib 1.1.1 documentation), a really full featured Python library. With it and a couple other pieces of freely available code, I can read data from .csv files into arrays that can then be directly used to generate a plot and save it to an image file. The code for this is really simple, as you'll soon see. The images are saved directly to the web server directory, from where I can grab them from any web connected machine (the plot images in this thread are pulled live from the Pi's web server).
As for the data amount, it's really less than it seems. The .csv files for each day are only about 6kBytes in size, the .PNG images about 55k. With a cheap 4GByte SD card in the Pi, I could store 100 years of data and still have room to spare.
I'd like to put additional sensors on it as well (at least one upstairs, one downstairs, and one outside), and will have to experiment a little with the maximum wire length. I'm using the DS18B20 sensor (also Dallas 1-wire) - do you have any idea how long the wires can be before you start getting problems with signal degradation?
09-25-12, 02:18 AM
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