User's Manual

Galaxy Tracking Systems, L.L.C. Technical Documentation - VTU
between the armed and disarmed states. The remaining input is used to sense activation
of the vehicle alarm system (if present).
7.2 Outputs
Each of the three Switch Box switches have an associated status LED output (pins 5-7 on
J1). When one of the silent alarm switches is pressed, the corresponding LED will flash
at a 1 Hz rate to indicate an alarm has been sent to the command center. When the alarm
is acknowledged, the LED lights continuously. The LED can only be extinguished (and
the alarm cleared) from the command center. The third LED is lit when the unauthorized
movement sensor is armed.
The fourth output (pin 8) drives an LED that indicates VTU power and blinks off
whenever the VTU transmits.
The remaining four outputs (pins 4, 5, 6 and 7) can drive small loads (<20mA) and must
be interfaced to real world circuits through high current drivers (MOSFETS) or relays.
These outputs are dedicated to the control of external devices such as vehicle accessories,
horns, etc.
8.0 VTU Operations
8.1 VTU Startup
The VTU initializes first time power is applied after installation. Most importantly, the
GPS receiver must find and track satellites, compute its position and synchronize to GPS
time. A clear view of the sky and the GPS satellite constellation is required to do this. If
the vehicle is parked in a garage or is shaded from the sky, it should be moved to a
location with an unobstructed view of the sky. The vehicle SHOULD REMAIN
STATIONARY until the GPS receiver has had time to initialize (30 minutes or less).
It is absolutely imperative that GPS initialize properly. All VTU and CBU
communications are synchronized to GPS time. An unsynchronized VTU may transmit
within some other VTU’s time slot (in which case both VTUs seem to disappear) or may
not transmit at all.
To verify that the VTU is ready for use, a series of commands are issued form the
command center. A number of ONE-SHOT commands are transmitted first. A ONE
SHOT requests a single response from the VTU no matter what its operating mode. Any
response from the VTU verifies the communication link and that VTU time keeping via
GPS has been established.
Next the VTU is commanded to IN SERVICE mode. Proper initialization of the VTU is
indicated when the correct time, GPS tracking status and position are returned to the
command center in the IN SERVICE response. If the status is not correct, additional
ONE-SHOT commands are transmitted to the VTU until the responses (IN SERVICE
messages) indicate that initialization is complete. At this point the VTU is ready for use.
Use or disclosure of data contained on this sheet is subject to the restriction on the title page of this report.