tailieunhanh - Practical Arduino Cool Projects for Open Source Hardware- P27

Practical Arduino Cool Projects for Open Source Hardware- P27: A schematic or circuit diagram is a diagram that describes the interconnections in an electrical or electronic device. In the projects presented in Practical Arduino, we’ve taken the approach of providing both a photograph and/or line drawing of the completed device along with a schematic. While learning to read schematics takes a modest investment of your time, it will prove useful time and time again as you develop your projects. With that in mind, we present a quick how-to in this section | C H A P T E R 13 Weather Station Receiver 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 your home and measure temperature wind speed and direction humidity rainfall and barometric pressure and the display unit that lives inside your home 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. Figure 13-1. La Crosse weather station installed on a roof 239 CHAPTER 13 WEATHER STATION RECEIVER Many weather stations transmit their data at approximately 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 about 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-consumption monitoring systems. Best of all there s no modification required to the original device because 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. Figure 13-2. Weather station sensors and transmitter being installed Once