Page 241 - Build Your Own Quadcopter_ Power Up Your Designs with the Parallax Elev-8

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

xb1.Str(String(“,”))
fv := GPS.Long_Hour ‘ Get Hour
If fv <> floatNaN
xb1.Dec(GPS.Long_Hour)
Else
xb1.Str(String(“---”))

xb1.Str(String(“,”))
fv := GPS.Long_Minute ‘ Get Minute
If fv <> floatNaN
xb1.Dec(GPS.Long_Minute)
Else
xb1.Str(String(“---”))

xb1.Str(String(“,”))
fv := GPS.Long_Second ‘ Get Second
If fv <> floatNaN
xb1.Dec(GPS.Long_Second)
Else
xb1.Str(String(“---”))
xb1.tx(13)
WaitCnt(ClkFreq / 2 + ClkFreq / 4 + Cnt) ‘ Wait .75 seconds to
repeat

DAT
floatNaN LONG $7FFF_FFFF ‘Means Not a Number

The above program uses the same XBee driver object, XBee_Object_1, as was the case in
the previous test programs. This program also uses a GPS driver object named GPS_Float_
Lite that takes care of all the necessary protocols between the GPS module and the Mini.
Retrieving data from the GPS module becomes very easy, since all that is required is to call
the GPS driver method that returns the desired data. For example, the following gets the
current GPS hour data:

fv := GPS.Long_Hour

Where fv is a local variable, GPS is the local reference to GPS_Float_Lite, and Long_Hour is
the name of the method in GPS_Float_Lite that returns the current GPS UTC hour value.
UTC is short for Coordinated Universal Time and is the time standard used to ensure that GPS
time reports become independent of any time zone.
Except for the deployed display, the receive portion of this system is the same as the one
previously described in the test system. I used the BOE with the laptop to test the prototype
system, which made sense because the portable display would not impact any essential data
transfers between the transmitter and receiver XBee nodes. The receiver-node connections
were detailed in Table 8.8, and the assembly was shown in Figure 8.23. Figure 8.27 is a laptop
screenshot showing the results of a trial run with the complete GPS system. The 10 data
elements displayed in the figure are detailed in Table 8.10 for your information. GPS data is