Sensors for automotive security systems. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Sensors for automotive security systems. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Automobile. Security devices and alarms

List of basic car alarm sensors

Vehicle swing sensor

This is a very simple sensor. Consists of two magnets and a coil. One magnet is fixed, and the second is installed in the magnetic field of the first in a suspended state.

In our country, such a sensor is most common in automotive security systems.

shock sensor

Operating principle: the sensor captures the vibrations of the car body. In the event that the vibration amplitude exceeds the specified value, an alarm is triggered.

Such sensors have a low cost due to their technical simplicity and are the most common in application. As a rule, they are supplied in the basic kit. One of the significant disadvantages of such sensors is their insensitivity to swing and high ability to respond to interference.

The shock sensor can be triggered, for example, by a shot, a salute, or a heavy truck passing by, but will remain indifferent to the unscrewing of the wheel of the car on which it is installed. It should be noted that modern car security systems are being improved more and more. And today, the alarm sensors of some manufacturing companies do not have the disadvantages mentioned above.

Ultrasound Scanner

The ultrasonic scanner reacts to movements in the car interior. His work is based on the interference of ultrasonic vibrations and the Doppler effect. The device consists of an ultrasound emitter and a receiver. These components are carried in the passenger compartment. The area controlled by the scanner is limited to the car interior with the windows closed. The ultrasonic scanner works effectively in expensive models. However, he has a few shortcomings, This is:

- low sensitivity to slow movements;

- the possibility of shielding the emitter with soundproofing material;

- false positives when exposed to convection air currents. Usually, an ultrasonic scanner is included in the basic alarm kits. But it can also be sold separately.

microwave scanner

Designed to detect movement both inside the cabin and near the car. The principle of operation of such a scanner is based on the interference of centimeter-range radio waves emitted by the sensor. Because this scanner is outside the vehicle and can cause false alarms, it needs careful setup to work effectively.

The microwave scanner does not pick up slow movements, which is one of its drawbacks. But its undoubted advantage is resistance to the perception of extraneous noise, the movement of warm air flows and vibrations. Among microwave scanners, there are models that have a two-threshold level. They allow you to implement scaring when approaching the car. At the first level of operation, the headlights of the car and a weak sound signal are turned on.

Glass break sensor

The sensor reacts to the sound of broken glass. There are one-threshold and two-threshold sensors. Single-threshold react to the sound of broken glass, even if it is an ordinary bottle, broken next to the car. The operation of such sensors depends primarily on the type of glass, its thickness, as well as on the location of the sensor relative to the glass. Two-threshold sensors register two signals: the sound of impact on glass and the sound of broken glass. The interval between these signals should be no more than 150 ms.

Voltage drop sensor

When electrical equipment is connected to the vehicle's electrical system, small voltage surges may occur. The sensor captures them, identifies the connection and signals the penetration into the car.

Typically, such a sensor is built into the central unit and is included in the basic set of many alarms.

The effectiveness of car alarms

When choosing a car alarm, the owner of the car pays attention, first of all, to how well the main task facing the system will be performed - the protection of his property.

Code keychain

A code key fob is a transmitter made in miniature. It usually works

in the range of decimeter waves (200-450 MHz). There are models of key fobs that work on infrared rays, but their range is much smaller. Code key fobs are used to protect the car alarm from unwanted shutdown by an unauthorized person. Such transmitters may differ in the level of secrecy of the codes. Modern models, as usual, have a very large number of coding options. Special chipsets are used for encoding and further decoding.

Antiscan

Anti-scanning implies the impossibility of disabling the alarm using a scanner by an unauthorized person.

A scanner is a device that sequentially reproduces codes in a hackable signaling format. It is impossible to disable anti-scanning by enumerating the key fob codes, since if you enter an incorrect code, this device will be in a blocked state for some time. The number of possible codes is huge, enumeration of all options in this case is simply unrealistic. However, this device has one drawback. At the moment of encoding the transmitter, its signals can be intercepted from the air using special devices (grabbers or code interceptors).

Dynamic code

Dynamic code (jumping, floating) has a technology that makes it impossible to select the code, as well as its interception from the air.

The real code is encrypted in such a way that with each transmission a completely different code information is emitted. Restoration of the actual code in the receiver occurs with the help of mathematical processing. Due to the impossibility of predicting which of the following code combinations will disable the alarm, intercepting codes is useless. A simple repetition of the previous message will not turn off the alarm, since they are all invalid.

In order to predict subsequent options, you need to know the code encryption algorithm and a large number of possible code samples of a particular transmitter (key fob).

Code combinations are repeated after a long period of time. The record of the identifier of the car alarm key fob with floating codes is made by the manufacturer and is unique. During operation, the code cannot be replaced.

The technology of floating codes reliably protects the alarm from hacking by electronic means.

Self-powered siren

Some car security systems, in addition to the direct function of protecting the car from electronic hacking, include devices that make it resistant to power failure.

One of the most affordable and fairly effective devices that increase the stability of the alarm system is a self-powered siren. In a situation where the burglar manages to de-energize the car's on-board network, it raises the alarm. The self-powered siren has built-in batteries and a control circuit that provides an audible signal when the power is turned off. It will work even if you take it out of the car.

Internal accumulators have constant recharging from the boreset.

Author: Korshevr N.G.

See other articles Section Automobile. Security devices and alarms.

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