User manual

LPCXpresso Experiment Kit - User’s Guide

Page 117

 If you have access to more than two XBee modules test what happens when they are all

powered.

 Change the protocol from broadcast mode to point-to-point communication by adding the

target node’s address in the xbee_send() function call.

7.16.2 Lab 15b: GPS Receiver

The Global Positioning System (GPS for short) is a satellite navigation system that provides time and

location information as long as there is a direct line of sight to at least four satellites. GPS is used in a

wide range of application including cell phones and car navigation systems.

In this experiment a GPS module from Embedded Artists (with the GPS chip from GlobalTop

Technology Inc) will be used. It is simple to use as there is no initialization of the module and it

continuously sends the received information on the UART channel explored in Lab14a-c. The baud

rate is specified by the module to 9600bps.

Note that the GPS module in not included in the component kit. It must be bought separately.

Figure 65 illustrates the GPS module mounted in RF module interface connector J15. The current

consumption is low for the module (ín the region of a couple of mA) so the shorting jumper can be

placed in position 1-2 on J12 (right position in picture below).

Figure 65 – GPS Module Mounted in J15

The module outputs a number of different messages in the NMEA 0183 format

(http://en.wikipedia.org/wiki/NMEA_0183). Each message starts with a dollar sign $ and ends with a

checksum. These are some examples taken from the manufacturer’s data sheet:

$GPGGA,064951.000,2307.1256,N,12016.4438,E,1,8,0.95,39.9,M,17.8,M,,*65

$GPGSA,A,3,29,21,26,15,18,09,06,10,,,,,2.32,0.95,2.11*00

$GPGSV,3,1,09,29,36,029,42,21,46,314,43,26,44,020,43,15,21,321,39*7D

$GPRMC,064951.000,A,2307.1256,N,12016.4438,E,0.03,165.48,260406,3.05,W,A*2C

The exact meaning of each of them is found in the data sheet but here we will focus on the one starting

with $GPGGA as it contains the time and location information.