High Performance Automotive Sonar Intrusion – Data Sheet

AS8412

March 2001

Page 11 of 14

VDD

WARN

DON’T CARE

DON’T CARE

VDD

WARN

DON’T CARE

DON’T CARE

( a )

( b )

stw

t

Fig. 6

(a) Self-Test OK

(b) Error at Self-Test

Alarm Signalling

The AS8412 can indicate not only intrusion or motion, but also other kinds of disturbance, and

send a particular message for each situation. Those disturbances are defined as follows and

the messages are identified at Table 3.

• Weak intrusion: early stages of an intrusion, or a weaker intrusion or movement. Detection

criteria are similar to those for intrusion, but with higher sensitivity.

• Blockage: elimination of the coupling between the transducers, either by blocking one of

them, or by cutting a wire.

• Saturation: very strong 40-kHz signal at RX, possibly an attempt to sabotage the alarm

system by saturating the receiver. May also be caused by a glass breakage or by strong hits

with hard objects at the glass.

With this signalling scheme, the IC has flexibility to be used either in simpler applications or in

sophisticated microprocessor based systems. In addition, the manufacturer has the option to

choose which kind of disturbance should be an alarm condition.

The pulse widths are those specified in the AC electrical Characteristics and shown in Fig. 7.

At ALARM and WARN they are at least 200ms; the outputs remain active if intrusion or motion

persists.

The WARN output could be used instead of the ALARM, if only intrusion detections should be

flagged. In this case, the digital sensitivity should be scaled one step ower (for instance from

mid-high to mid-low), or the capacitor at VCAP increased, to keep approximately the same

sensitivity.