High Performance Automotive Sonar Intrusion – Data Sheet

AS8413

March 2001

Page 7 of 15

Optionally one of the AS8413 ICs used in a system may have its built-in oscillator and generate

clock to the other IC from its COSC output. A driver would be needed, if IC’s are not adjacent.

Master/slave synchronization

The AS8413 is intended to be used in intrusion detector systems where more than one pair of

transducers is used. Each IC is able to control a single transmitter /receiver pair. In multiple-

transducer systems it is necessary that the bursts generated by each transmitter are synchro-

nized. Otherwise, the echoes may slip over each other and cause undesirable effects, such as

false alarms.

Each AS8413 IC can be programmed to be either a master that generates an external delayed

sync signal or a slave. This signal may come from the master or from an external circuit, such

as a microcontroller. The sync signal received at the slave is delayed by half transmission period

(22.2 ms) to the internal sync signal used by the master, in order to avoid burst superposition as

much as possible.

The AS8413 can be configured to operate under 3 possible conditions, by programming the

MODE input in one of the three possible conditions:

• logic ‘0’: slave (receives delayed sync)

• logic ‘1’: master in a multi-pair system (generates delayed sync)

• open: master in a single-pair system (AS8412 mode)

Ultrasonic Transducers

The AS8413 is compatible with standard 40-kHz ultrasonic transducers, available from several

manufacturers. For each IC, one transducer is used to transmit the sonar pulses and one other

to receive the echoes reflected inside the vehicle. Internal lengths up to 3.5 meters can be cov-

ered.

In most applications, just two pairs of sensors will be used. The sensors will typically be posi-

tioned at the B-pillars (central pillars), close to the roof, to provide the best possible coverage of

all the vehicle interior. Each pillar may have either a transmitter/receiver pair or two sensors of

the same kind. The first arrangement is recommended, as it allows a single box at each pillar

containing the AS8413 and the transducer pair controlled by it, thus decreasing cabling.

The outputs TX1 and TX2 drive the transmitter in a push-pull configuration with 10 V peak-to-

peak. As shown in Fig. 1, the transmission duty-cycle is very short (around 1/75), reducing the

average current needed to generate the ultrasonic bursts to about 0.05 mA per IC.

Shielded cable is mandatory for the receiver and recommended for the transmitter, unless they

are adjacent to the IC. The shield at the receiver cable must be grounded and connected to the

RXGND pin.