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230     Bu il d  Y o ur  O w n  Q u a d c o p t e r



























                             Figure 8.35  Google Earth screenshot.



                                Ensure that there is one space between each element and that descriptors N and W are
                             also present. Of course, the N and W descriptors will change depending upon where you
                             operate the quadcopter. Figure 8.35 shows the resultant Google Earth screen when the above
                             coordinates were entered into the Search text box.
                                This section completes my discussion of how to achieve good situational awareness
                             when operating the quadcopter while using a real-time GPS system. The next chapter shows
                             you how to add real-time video capability that will greatly complement this GPS system.


                        Summary
                             I began the chapter with a brief history of the GPS system followed by a tutorial that used a
                             fictitious example to explain the basic underlying principles governing the system.
                                The PMB-688 GPS receiver was discussed next, focusing on its excellent receiver
                             characteristics as well as its easy serial communication link.
                                I discussed how to set up and test the GPS module with a serial-console link by using a
                             USB/TTL cable. The Propeller Serial Terminal (PSerT) was run on a Windows laptop to
                             verify proper operation of the GPS module.
                                The NMEA 0183 protocol was thoroughly examined to illustrate the rich set of messages
                             that are created by the GPS receiver. This project uses only a small subset of the data, but you
                             should be aware of what is available for potential use. A look at a parsed GPS message was
                             also included along with a brief explanation of how to interpret latitude and longitude data.
                                The next item introduced was the new Propeller Mini, which is a very compact Parallax
                             Propeller development module. This module supports the full Spin language with a full
                             complement of  general-purpose input/output (GPIO) pins. I used the Mini as an onboard
                             controller for both the GPS module and an XBee RF transceiver.
                                I also carefully explained Zigbee, which is the XBee data communication protocol. It is
                             important to understand how Zigbee works because it is a key part of the control program
                             that runs in the controlling microcontroller.
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