Issue
151 February 2003
GPS-GSM
Mobile Navigator
ACCESSORIES
An
AT45D021’s serial-interface flash memory is used as
a black box to store data packages. The 2,162,688 bits
of memory are organized as 1024 pages of 264 bytes each.
In addition to the main memory, the micro also contains
two data SRAM buffers of 264 bytes each. The simple
SPI serial interface facilitates the hardware layout,
increases system reliability, and reduces the package
size and active pin count. The AT90S8515 saves GPS data
to flash memory via an SPI port at a user-defined specific
interval. Or it reads data from the flash memory to
backup to PC. Up to 2160 pieces of information can be
stored in flash memory.
Because
the AT90S8515 has only one UART port, another chip is
used to expand the serial port for three kinds of different
functions. The digitally controlled MC14052B analog
switch is a dual four-channel multiplexer. With two
I/O pins, the AVR controls it to switch among three
channels, all of which are UART serial interfaces.
One
MAX202 chip accomplishes the conversion between TTL/CMOS
level and RS-232 level, which is necessary for the RS-232
interface between the navigator and PC. Using the RS-232
port, the system can backup the data in flash memory
to the PC. Also, you can change some system parameters
through the PC via the RS-232 port.
With
two control pins and four data pins, the AVR gives the
LCD specific information to display. Port pins PC2 through
PC4 individually sense the three push-button switches.
There is a Menu button to select the work mode, and
an Enter button to confirm the selection. The third
is an SOS button used to send an alarm message to the
control center.
SOFTWARE
DESCRIPTION
We
used the powerful BASCOM-AVR to develop the software.
An IDE is provided with an internal assembler. You can
also generate Atmel OBJ code. Additionally, the BASCOM-AVR
has a built-in STK200/300 programmer and terminal emulator.
Other notable features include: structured BASIC with
labels; fast machine code instead of interpreted code;
special commands for LCDs; I2C; one wire; PC keyboard
and matrix keyboard; RC5 reception; and RS-232 communications.
The BASCOM-AVR has an integrated terminal emulator with
download option, an integrated simulator for testing,
and an integrated ISP programmer.
You
can easily write the firmware for this project using
the BASCOM-AVR. And with the ISP benefit of AVR, on-line
emulation is almost unnecessary, so you can program
and test with ease. The flow charts in Figures 3 and
4 describe the AT90S8515 program that controls the devices.
The software handles a number of key functions, such
as initializing the system and starting the GPS and
GSM modules. The software also selects the working mode.
Additionally, it checks and sets the system parameters
in mode 0, backs up the trace data stored in flash memory
to the PC in mode 2, and resets the system parameters
in mode 3.
|
(Click
here to enlarge)
|
Figure
3—After initialization, you can select the function
mode by pressing the Menu button and Enter button.
The LCD will show the status and system parameters. |
|
(Click
here to enlarge)
|
Figure
4—The main function is mode 1. The AT90S8515 microcontroller
receives the ship location data every 2 s from the
GPS module, and then saves the data in flash memory
every 20 s. At a user-defined time interval, the
AT90S8515 sends the location data to the control
center, and then receives the control information
from the control center via the GSM module. |
Mode
1 is the standard working mode during which many tasks
are completed. During mode 1, the GPS signals are read
every 2 s from a satellite; the location information
is saved in flash memory every 20 s; and the GSM module
sends location data to the control center according
to the given interval time. Meanwhile, the navigator
receives the control information from the control center
from the GSM module.
APPLIED
TECHNOLOGY
Our
system is now being used in Shanghai Port, China for
navigation and monitoring of ships. Aside from tracking
ships, the GPS-GSM Mobile Navigator can also find use
in other applications, such as navigating taxis. The
system works quite well, and we plan to adapt it for
future projects.
