SL869-3DR Evaluation Kit User Guide
1VV0301266 r0
2016-11-14
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Page 11 of 35
Mod. 0810 2011-07 Rev.2
2.1.
Classic Dead Reckoning (DR) Description
In a Classic DR configuration, a discrete odometer or wheel pulse signal is required to provide
the unit with vehicle speed data. This signal may be obtained from various locations in the
vehicle such as the transmission, speed display or ABS system.
Another option for supplying the odometer or wheel tick pulse is through the on-board
diagnostics (OBDII) connector, which provides access to the vehicle’s controller area network
(CAN) bus. This can be achieved with the addition of an “OBD VSS Signal Generator” - a device
that generates a wheel pulse from the vehicle CAN bus data. Telit does not sell these devices.
A forward/reverse signal, usually provided by the vehicle’s transmission or a backup light circuit,
supplies directional data to the DR module. For proper operation, the reverse signal should be
stable when on and not be pulsed.
A DR module also includes a rate gyro that measures angular acceleration (rate of heading
change), allowing the unit to maintain vehicle heading data.
Figure 2-2 Classic DR Operation
Note that these connections to the vehicle systems are not required for MoDR operation, as
described in the next section.
