tailieunhanh - Practical Arduino Cool Projects for Open Source Hardware- P28

Practical Arduino Cool Projects for Open Source Hardware- P28: 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 | CHAPTER 13 WEATHER STATION RECEIVER To increase the sensitivity of the receiver it needs an external antenna. Radio antennas need to be tuned to the correct wavelength for the frequency you are listening for and the wavelength of a 433MHz signal is approximately 69cm or 27in. A good tuned length to go for in this case is 1 2 wavelength which is or . We need to allow a little distance for the length of the pin and track so we ll create an antenna just slightly shorter than half-wave. Cut a piece of lightweight hookup wire about 33cm 13in long and strip back a few millimeters from one end then tin it with solder so it s ready to connect to the board. On the prototype we soldered the end of the antenna to a female header so it could be easily removed from the board. Having a 33cm piece of wire hanging loose might not be very convenient so to keep things neat you can wrap it around a nonconductive former so that it forms a widely spaced coil. Our prototype antenna is wrapped around a piece cut from the body of a ballpoint pen and held in place with tape but if you wanted to make it look a bit neater you could slip a length of heat-shrink tubing over the top to hold everything in place see Figure 13-11 . Figure 13-11. Antenna wrapped around body ofballpoint pen You should now have a fully assembled receiver shield ready to go so plug it into your Arduino and connect it to your computer via USB see Figure 13-12 . 249 CHAPTER 13 WEATHER STATION RECEIVER Figure 13-12. Arduino receiver and antenna assembled and ready for use Weather Station Receiver Program The program for this project is one of the more complex ones in the book and uses a number of things you might not have seen in Arduino sketches before. It s fairly long so you definitely shouldn t bother trying to type it all in just download it from the project page on the Practical Arduino web site at projects weather-station-receiver. Unlike many Arduino programs it s not all .

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