High Performance Automotive Sonar Intrusion Data Sheet
AS8412

March 2001

Page 2 of 14

Key Features

True sonar/pulse-echo operation

Wide dynamic range

Programmable sensitivity levels

Self-adaptive to vehicle interiors

Self-adaptive to temperature and environmental changes

High sensitivity to intrusion

Immunity to false alarms

Detection of sabotage attempts

Compatible with standard 40 kHz ultrasonic transducers

No adjustments needed at factory or at field

Few external components

Time reference: external clock or oscillator based on crystal/ceramic resonator

Built-in self-test

Internal power-on-reset

Advanced CMOS technology

Low power consumption: 0.65 to 1.0 mA

Operation between -40°C and +85 °C

Available in 20-pin DIP and 20-pin SOIC package

General Description

The AS8412 is a signal processing IC designed to implement reliable, high-performance

sonar intrusion detectors. It generates short 40 kHz bursts to feed an ultrasonic trans-

ducer. The resulting sonar waves are reflected on the vehicle interior and the echoes are

received by another transducer. Inside the AS8412, the electrical signal is first submitted

to an analog conditioning circuit, then it is digitized and processed by a DSP, whose out-

put is analyzed by a discriminator based on fuzzy-logic techniques. Thus, true intrusion

conditions can be discerned from natural phenomena and other allowable disturbances.

No adjustments are necessary at factory or at the field, as the AS8412 is self-adaptive to

the physical and environmental conditions. Compact and EMI-resistant intrusion detec-

tors are made possible, due to the small number of components.

Block Diagram

PRE-

AMP

BAND-PASS

FILTER

AGC

ENVELOPE

DETECTOR

A / D

CONVERTER

D S P

DISCRIMINATOR

MODULATOR /

DRIVER

CONTROL

LOGIC

OSCILLATOR

SIGNALLING

VCAP

SAS
SENS 1

SENS 0

ALEN
LED
WARN

ALARM

SEL40K

OSCIN

OSCOUT

TX1

TX2

High Performance Automotive Sonar Intrusion Data Sheet
AS8412

March 2001

Page 3 of 14

Pin Description

AS8412

Pin #

Name

Description

TX1

40-kHz burst generator - output 1.

OSCIN

Clock input or crystal / ceramic resonator connection.

OSCOUT

Crystal / ceramic resonator connection. Not connected when external clock is applied.

VCAP

Pin for programming capacitor at the envelope detector.

AVDD

Analog supply voltage (+5V).

AGND

Analog ground.

RXGND

Analog ground.

Ultrasonic echo input.

SEL40K

Time reference select input (SEL40K='1' to select 40 kHz or SEL 40K='0' to select 400 kHz
at OSCIN).

ALEN

Alarm enable input (when ALEN ='0', the outputs ALARM, WARN and LED are disabled).

SENS0

Sensitivity selection (least significant bit).

SENS1

Sensitivity selection (most significant bit).

SAS

SAS enable input (SAS='1' activates Self-Adjusting Sensitivity, SAS='0' keeps sensitivity
fixed)

Test / reset pin. A rising edge resets the IC. This pin should be left unconnected or tied to
VDD for normal operation.

VDD

Digital supply voltage (+5V).

GND

Digital ground

LED

Active-low signalling LED output (open drain).

WARN

Active-low auxiliary alarm output (open drain).

ALARM

Active-low main alarm output (open drain).

TX2

40-kHz burst generator - output 2.

Pinout & Packaging

Available Package(s):

20 pin DIP

20 pin SOIC

TX1

OSCIN

OSCOUT

VCAP

AVDD

AGND

RXGND

SEL40K

ALEN

TX2

ALARM

WARN

LED

GND

VDD

SAS

SENS1

SENS0

High Performance Automotive Sonar Intrusion Data Sheet
AS8412

March 2001

Page 4 of 14

Absolute Maximum Ratings

Conditions: 1. AII voltages referenced to GND

2. AVDD connected to VDD

3. AGND connected to GND

Supply Voltage

< 7V

Input Pin Voltage

-0,3 V to VDD + 0.3 V

Output Pin Voltage

-0,3 V to VDD + 0.3 V

Power dissipation

500 mW

Operating temperature under bias

-40 °C to +85 °C

Storage Temperature

-65 °C to +150 °C

Latch-up immunity

-10mA ... + 10mA

Note:

Stresses above these values may cause permanent damage to the device.

Functional operational at these values is not implied

ESD immunity / HBM: 1500 Ohm; 100 pF

Recommended Operating Conditions

Parameter

Symbol

Min

Typ

Max

Units

Supply Voltage (VDD, AVDD)

4.5

5.0

5.5

Operating Temperature Range

-40

°C

Clock Frequency (SEL40K=1)

kHz

AC Peak Voltage at RX Input

0.1

D.C. Electrical Characteristics

= 5 V, V

= Ground, T

= -40 °C to +85 °C)

Parameter

Symbol

Min

Typ

Max

Units

Conditions

Low Level Input Voltage

1.5

Pins 2, 9, 11, 12, 13

High Level Input Voltage

3.5

Pins 2, 9, 11, 12, 13

Low-to-High Threshold

3.0

3.5

Pin 10 (Schmitt Trigger Input)

High-to-Low Threshold

1.4

1.8

Pin 10 (Schmitt Trigger Input)

Hysteresis

0.6

Pin 10

Low Level Input Current

-1

µA

Pins 9, 10, 11, 12, 13, (V

=5 V)

High Level Input Current

µA

Pins 9, 10, 11, 12, 13, (V

=5 V)

Input Resistance

200

Pin 8

High Performance Automotive Sonar Intrusion Data Sheet
AS8412

March 2001

Page 5 of 14

Low Level Output Voltage

Vol

0.5

Pins 1, 20

Pins 18, 19

Pins 17

Iol=3 mA

Iol=4 mA

Iol=12mA

High Level Output Voltage

Voh

4.0

Pins 1, 20

Ioh=-3 mA

High-Z Output Current

Ioz

µA

Pins 17, 18,
19

Vo=5V

Total Supply Current

Idd

0.65

1.0

1.6

SEL40K= 1

SEL40K= 0

crystal or clock

ceramic resonator

C1=C2=100pF

A.C. Electrical Characteristics

= 5 V, V

= Ground, T

= 25°C)

Parameter

Symbol

Min

Typ

Max

Units

Conditions

Power-on-reset width

por

500

530

800

SEL40K= 0, resonator / clock

SEL40K= 1, clock

SEL40K= 1, crystal

Self-test delay (incl. t

por

)

std

1.3

1.7

1.4

1.9

2.1

SEL40K= 0, resonator / clock

SEL40K= 1, clock

SEL40K= 1, crystal

Fault indication pulse width

stw

4.3

4.6

ALARM low pulse width

200

Pins 18, 19

LED low pulse width

onn

977

narrow = no detection

wide = detection

LED high pulse width

off

888

System Description

Ultrasonic intrusion detectors are very popular in vehicle security systems, due to their low

cost, good area coverage and easiness of installation. The AS8412 uses the sonar principle to

build a high-performance intrusion detector that follows the requirements of the OEM automo-

tive industry. As very short ultrasonic bursts are sent, the power needed to drive the transmitter

is reduced. Interference and signal cancellation effects, present in systems with continuous

transmission, are virtually eliminated.

Fig. 1 shows the pulse/echo timing generated by the AS8412.

The basic concept behind the AS8412 is the detection of changes in the relative position of

objects inside the vehicle, by monitoring successive echo patterns with a discriminator based

on fuzzy-logic.

Despite the higher complexity of this approach, that demands both analog and digital signal

processing, the solution is made cost-effective with the use of a single IC and a small number

of external components.

High Performance Automotive Sonar Intrusion Data Sheet
AS8412

March 2001

Page 6 of 14

TX pulse

Echo in RX

44,4ms

0,6ms

Fig. 1 - Pulse/Echo Timing

Supply / Power-On Reset

The AS8412 requires a single 5-volt power supply. Pins for VDD and GND are separated for

the analog and digital circuits, and a 100 nF ceramic decoupling capacitor is recommended for

each pair.

There is an internal power-on-reset circuit that initializes the IC after each power-up. The VDD

rise time must be less than 20 ms, to guarantee proper initialization. Optionally, the IC can also

be reinitialized with a rising-edge at the pin 14, if requested by the application.

Time Reference

A clock must be present at the OSCIN input. The frequency may be selected to be either 40

kHz or 400 kHz, by setting the SEL40K input to `1' or `0' respectively. For the 40 kHz clock a

duty-cycle of approximately 50% is necessary.

The clock signal can be created in several possible ways:

Generation by a microprocessor or other external circuit

Built-in oscillator with an external 40-kHz crystal between OSCIN and OSCOUT. Depending

on the crystal, a load capacitor (about 22 pF) may be needed at OSCOUT.

Built-in oscillator with an external 400-kHz ceramic resonator between OSCIN and

OSCOUT.

Load capacitors of at least 100 pF are necessary at the pins, according to the resonator speci-

fications. The IC power consumption increases with higher capacitor values (I

= 1.0 mA with

100 pF capacitors).

Ultrasonic Transducers

The AS8412 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

High Performance Automotive Sonar Intrusion Data Sheet
AS8412

March 2001

Page 7 of 14

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 AS8412 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.

Analog Conditioning

The analog front-end, composed of a preamplifier and a filter centered at 40 kHz, increases the

signal level and removes noise outside the bandpass. It is followed by a digitally controlled AGC

amplifier, which keeps signal level at the VCAP output within prescribed levels. Finally, an en-

velope detector extracts the information embedded in the amplified echo signal.

The front-end needs proper bias during power-up. That can be provided by an RC series circuit

to VDD, as shown at Fig. 2, or alternatively, by the pre-amplifier of Fig. 4.

VDD

100n

100k

To RX-Pin

Fig. 2 - Series-RC circuit at RX

The AS8412 has a wide dynamic range, to follow the signal fluctuations that occur in a large

variety of vehicles, sensors and environmental conditions. Only under extreme conditions, like

in a larger vehicle, an external pre-amplifier at RX may help to improve performance.

A practical way to verify if a pre-amplifier might be useful, is by monitoring the echo waveform

at VCAP. A FET-input buffer (input impedance at least 10

ohm) should be used, as the output

impedance at VCAP is very high.

T(ms)

Period = 44,4 ms

VCAP(V)

3,0V-4,2V

1,3V-1,8V

Fig. 3 - Waveform at VCAP

High Performance Automotive Sonar Intrusion Data Sheet
AS8412

March 2001

Page 8 of 14

As a general rule, the best approach is to measure the voltage at the "valley", that normally

occurs at the end of the echo waveform. If it is above 1.8 V, then the system could benefit from

some extra gain.

A pre-amplifier that satisfies the bias requirements is shown at the Fig. 4. Its gain is around

8 dB.

Fig. 4 - Recommended pre-amplifier

Sensitivity Programming

The AS8412 allows the sensitivity to intrusions and movements to be programmed at produc-

tion, so the manufacturer can adapt the detector to different requirements.

There are two possible ways of programming the sensitivity:

Digital programming by the pins SENS1 and SENS0: controls the criteria used by the dis-

criminator to validate intrusions or movements. Four sensitivities are available, as shown at

Table 1.

Table 1. Digital programmable sensitivities

SENS1

SENS0

Sensitivity

High

Mid-high

Mid-low

Low

Capacitor at the pin VCAP: controls the analog processing of the echo signal at the enve-

lope detector. With smaller capacitors, the digitized echo signal will have a higher resolution

and, as a result, a higher sensitivity will be obtained.

The best combination of digital programming and VCAP capacitor is usually determined by

experiment. A generally good choice is to use sensitivity mid-high and 270-pF capacitor at

VCAP.

High Performance Automotive Sonar Intrusion Data Sheet
AS8412

March 2001

Page 9 of 14

Table 2 shows some possible sensitivity combinations, marked according to the expected be-

havior at the field. It should be used as a guide to determine the best combination for each ap-

plication.

Table 2. Sensitivity as Function of Digital and VCAP Programming

PROGRAM

390 pF

330 pF

270 pF

220 pF

High

Mid-high

Mid-low

Low

(+) positions with higher sensitivities; may present false alarms under extreme conditions

(OK) most usual sensitivity combinations

(-) positions with lower sensitivities; may be useful for specific applications

The Self-Adjusting Sensitivity (SAS)

The SAS (Self-Adjusting Sensitivity) control loop is a powerful feature that optimizes the sensi-

tivity to intrusion and motion, based on the present environmental conditions. Under quiet situa-

tions the detector has a very high sensitivity. On the other hand, when certain disturbances

such as thermal gradients appear inside the vehicle, the sensitivity is decreased to avoid pos-

sible false alarms.

The sensitivity range programmed by the manufacturer is not changed by the SAS, that simply

selects the most adequate sensitivity for each situation within the allowed range. Fig. 5 gives a

rough idea of how the SAS can affect the detector sensitivity, for a given capacitor at VCAP.

H I G H

L O W

M I D - L O W

M I D - H I G H

S E N S I T I V I T Y

Fig. 5 - Sensitivity Ranges with SAS

The SAS actuation is controlled by the SAS input.

SAS enabled (pin SAS = "1"):

After power-on, the IC starts with the lowest sensitivity within the programmed range. The

sensitivity will be constantly adjusted, according to the external conditions. Even under quiet

conditions, the IC may take at least 2 minutes to reach the maximum allowed sensitivity.

That should be considered during system evaluation.

High Performance Automotive Sonar Intrusion Data Sheet
AS8412

March 2001

Page 10 of 14

SAS disabled (pin SAS = "0")

The IC will keep the sensitivity fixed at the upper limit of the programmed range, regardless

of the environmental conditions. This mode can be useful in special applications that de-

mand a fixed or externally controlled sensitivity. The VCAP capacitor may have to be up to 4

times

bigger than it would be with the SAS enabled, to compensate the fixed high sensitivity and

avoid false alarms. Another use of this mode is to allow an easier characterization of the

upper sensitivity limit during the system development.

The self-test indicates an error with SAS="0". To generate a valid self-test, SAS must be `I'

during power-up. It may be switched afterwards.

Together with the AGC, the SAS loop provides improved controllability over the intrusion detec-

tion process, allowing the system to be little affected by changes in the external conditions,

such as temperature, supply voltage and sensitivity of the ultrasonic sensors.

In any case, the sensitivity can be very significant, so the AS8412 is not adequate to be used in

convertibles or with open windows.

DSP and Fuzzy-Logic Discriminator

Many external phenomena may affect the ultrasonic waves inside the vehicle. Sunlight, blows

at the glasses or roof, wind through the ventilation flaps are some examples.

Experiments have shown that a real intrusion can not be validated by a single specific charac-

teristic of the echo waveform. Several parameters must be observed at the same time and

also how they correlate with each other. Experimental data gathered from extensive field test-

ing were used to support the detection criteria embedded in the AS8412.

To implement those criteria, first the digitized echoes are processed by a DSP circuit to en-

hance the parameters to be monitored. Then, a fuzzy-logic discriminator continuously exam-

ines how those parameters change and correlate, to verify any possible intrusion.

Built-In-Self-Test

When power is applied and SAS = "1", the AS8412 goes automatically into a self-test routine

that checks the IC operation. It can also detect initialization errors due to a slow supply rise

time or a clock problem at OSCIN.

During the self-test period, the IC outputs are exercised and should be ignored. If the test is

successful, normal operation starts, indicated by the output LED pulsing periodically.

In the case of an IC malfunction, immediately after the self-test the LED and WARN outputs are

turned on (low) for about 4.4 seconds. If a light-emitting diode is connected to the LED output,

the self-test message may be seen directly by the user.

After an error message, the LED starts to blink again, as in a normal operation. Fig. 6 shows

the possible self-test waveforms after power-on.

High Performance Automotive Sonar Intrusion Data Sheet
AS8412

March 2001

Page 11 of 14

VDD

WARN

DON'T CARE

std

off

onn

VDD

WARN

DON'T CARE

onn

off

std

( a )

( b )

stw

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.

High Performance Automotive Sonar Intrusion Data Sheet
AS8412

March 2001

Page 12 of 14

The blockage and saturation are signalized just one time at each occurrence, to avoid continu-

ous alarm triggering. Detection of glass breakage by saturation is not guaranteed.

Table 3. Disturbances detected by the AS8412

LED

ALARM

WARN

Conditions

pulsing

no disturbance

pulsing

weak intrusion

intrusion

pulsing

blockage

saturation

WARN

ALARM

ONW

ONN

Fig. 7 - Weak Intrusion followed by an Intrusion

Courtesy Entry/Exit Time

The pin ALEN is an optional alarm enable input that can be used to provide a courtesy entry

and/or exit time. When tied to VDD, normal alarm operation is enabled. If ALEN is grounded,

the outputs ALARM, WARN and LED are disabled, except during the self-test, when LED indi-

cates the test result.

By grounding ALEN, the IC can be made inoperative as seen by the control unit and still keeps

its internal processing. This is useful when intrusion detections must be temporarily inhibited,

or to block self-test pulses at ALARM and WARN.

During the first 10 or 20 seconds after shutting a door in a hot and sunny day, an alarm indica-

tion may occur, due to thermal gradients inside the vehicle. That should be considered when

choosing a courtesy time for an AS8412-based system. When an RC circuit connected to the

supply voltage is applied to ALEN, the courtesy time after power-up is given by:

0.92 x R x C

High Performance Automotive Sonar Intrusion Data Sheet
AS8412

March 2001

Page 13 of 14

Application Circuits

The AS8412 is designed to provide a flexible utilization, so many application circuits are possi-

ble. Only two of them are presented.

The Application Circuit I of Fig. 8a is suitable to be used in a microcontroller-based alarm sys-

tem. The 40-kHz clock is synthesized by the microcontroller, that also controls the digital sen-

sitivity. By having access to all the signalling outputs, the alarm system can be programmed to

signalize any combination of the disturbances detectable by the AS8412.

This arrangement uses a minimum number of components to implement an intrusion detector.

TX1

OSCIN

OSCOUT

VCAP

AVDD

AGND

RXGND

SEL4OK

ALEN

TX2

ALARM

WARN

LED

GND

VDD

SAS

SENS1

SENS0

UT1

40kHz

from

µ-Processor

N.C.

VDD

100n

100k

100n

UT2

µ-Processor

Programmable

Sensitivity

(Digital)

SAS Control

N.C.

VDD

100n

Fig. 8a - Application Circuit I

TX1

OSCIN

OSCOUT

VCAP

AVDD

AGND

RXGND

SEL4OK

ALEN

TX2

ALARM

WARN

LED

GND

VDD

SAS

SENS1

SENS0

100k

100p

UT2

VDD

Programmable

Sensitivity

(Digital)

N.C.

VDD

100n

VDD

N.C.

100p

100n

UT1

CR1

To Control Unit

Fig. 8b - Application Circuit II

High Performance Automotive Sonar Intrusion Data Sheet
AS8412

March 2001

Page 14 of 14

The Application Circuit II of Fig. 8b can be used in a simpler system, that does not need micro-

controller. A 400-kHz oscillator is built with a ceramic resonator. By using just the ALARM out-

put, the system is able to detect intrusion, blockage and saturation as alarm of the operation

and of the IC self-test diagnostic. A courtesy time is provided by R3 and C7.

EMI Protection

The usual precautions against EMI, such as PCB with ground plane, short tracks and shielded

cables, are recommended for AS8412 applications, to avoid possible effects from noise in-

duced by external sources.

The RX cable must be shielded, because of the low-voltage signal. An alternative to protect

other pins directly connected to unshielded cables, is to clamp induced voltages with signal

diodes close to the pins (Fig.9)

If a single shielded cable is used for the transmitting sensor, the internal wire may be con-

nected to TX1 and the shield connected to TX2. In this case, only the TX2 output will need pro-

tection diodes

V D D

(a)

(b)

Fig. 9 - Diode Clamp Protection for

Unshielded Cables

(a) pins 1, 20

(b) pins 17, 18, 19

2000, Austria Mikro Systeme International AG, Schloß Premstätten, 8141 Unterpremstätten, Austria.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by
any means, without the prior permission in writing by the copyright holder. To the best of its knowledge, Austria Mikro Systeme
International asserts that the information contained in this publication is accurate and correct.

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