Weather Station Receiver
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Copyright 2009 Marc Alexander <marc.alexander@gmail.com>
Copyright 2009 Jonathan Oxer <jon@oxer.com.au>

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| This project is featured in the book "Practical Arduino" by         |
| Jonathan Oxer and Hugh Blemings (Apress, 2009). More information    |
| about the book and this project is available at:                    |
|                                                                     |
| www.practicalarduino.com/projects/medium/weather-station-receiver   |
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The incredible popularity of home weather stations shows that it's not
just farmers who are interested in the weather. Many people want to be
able to track and record weather events within their local environment
rather than relying on a state or national weather service that may not
have adequate local details.

Home weather stations typically consist of two major parts: the sensors
that sit outside and measure temperature, wind speed and direction,
humidity, rainfall, and barometric pressure; and the display unit that
lives inside in a convenient place so you can read the external
temperature while sitting around the fire warming your feet and
deciding whether it's too cold to go fishing. Generally the external
sensors connect together with cables with one sensor also acting as a
transmitter to send updates wirelessly to the display unit.

Many weather stations transmit their data at about 433MHz using a band
reserved for low-power unlicensed use, which is ideal from a hacker's
perspective because 433MHz receiver modules are commonly available for
under $10 and can be easily interfaced with an Arduino to let you
eavesdrop on the data feed. In fact it's not just weather stations that
use this approach: many short-range wireless devices work on the same
433Mhz band so the techniques used in this project can be just as easily
applied to intercepting data from other devices such as domestic power
usage monitoring systems. Best of all there's no modification required
to the original device: it just transmits its data as usual, not even
aware that it's being received and interpreted by another device. This
project is essentially an exercise in listening to an unknown wireless
data feed and converting the raw stream of data into values that make
sense.

Once you can receive the data and process it in your Arduino there are a
wide range of things you can do with the information: you can simply
display it as it updates, or you can log the readings and generate
reports of trends over time, or you can even use it as the basis for
making decisions such as feeding rainfall data to an irrigation system
to minimise water usage.

For this project we used a weather station from La Crosse, a popular
brand that seems to be available in many parts of the world, but the
same approach should work with other brands - as long as you can work
out the data format! In fact many weather stations (including the La
Crosse model we used) come with a serial interface on the display unit
to feed data to a PC, but by doing the work directly in an Arduino with
a receiver module you don't even need the display unit at all. And since
many weather station sensors are available individually you may find you
can buy just the sensors you want and save some money compared to buying
a complete system, while also gaining the flexibility of managing the
data through an Arduino.

NOTE: This code is still very preliminary and full of debug information
used while interpreting the comms protocol. Please don't judge it by
its current state!