Almost every owner of a car equipped with an alarm is familiar with the situation when the security system considers it its duty to work from any strong and close source of vibration. In general, such cases are not considered something unusual, and with their rather rare occurrence, they do not particularly strain either the motorist himself or those around him. The situation is somewhat different when the parking lot is located near the construction site (with all the related ones in the form of jackhammers, compressors, pile driving mechanisms, etc.) or, in general, near the military airfield where jet fighters are based. At this point, the alarm begins to “howl” with an annoying frequency and the owner of the car is forced to either bring the sensitivity of the shock sensor to the lowest limit (such a setting ceases to be a hindrance for many “specialists” in removing wheels) or to completely turn off the security system. It would seem that the situation is hopeless, but there is still a solution to the problem and it consists in using, instead of (or parallel to it) a regular shock sensor, another measuring element that registers not only vibration and shocks of various levels, but also the tilt of the car body (when landing driver, installing a jack, opening the trunk, removing the external spare wheel, etc.).
The first version of the oscillation sensor
Even today, various measuring and household appliances use not digital, but pointer indicators, the operation of which is based on measuring the current passing through the coil, as a result of which an alternating magnetic field was formed that interacted with the field of a permanent magnet and thus deployed a measuring element equipped with an arrow . As it turned out, such pointer milliammeters are able to successfully operate in the reverse mode, in other words, if the coil physically moves in the field of a permanent magnet (for example, when the gravity vector changes), small currents will be generated in its turns, which are quite easy to measure.
In general, the idea is to place the milliammeter upside down, when the arrow, equipped with a small load, begins to play the role of a kind of pendulum, when moving which a proportional voltage appears at the outputs of the device. To amplify such an output signal, you need to create a fairly simple circuit using a minimum of components.
As a weight attached to the end of the arrow, you can use a small section of insulation from a wire of the appropriate diameter. If we use two milliammeters installed at an angle of 90° with respect to each other and connect them in series, it becomes possible to register oscillations along two axes. A 741 series op amp (or equivalent) is used as the basis for the circuit. With the help of a variable resistor with a nominal value of 4.7 kOhm, the sensitivity of the sensor is changed within a fairly wide range. As for the type of milliammeter used, its choice here is not critical, the main thing is that a resistor is not connected in series with the coil (however, you can simply remove it). If desired, the sensor can be powered from an autonomous battery. The output signal is taken between the "OS" points and the plus of the power source.
The second version of the oscillation sensor
In this case, as a source of signals, it is proposed to use the magnetic frame of the M476 / 1 microammeter in previous years, widely used as a recording level meter on many tape recorders, including portable cassette players. To manufacture a sensor, such a microammeter should be opened (this operation can be done using a conventional knife).
Further, at the end of the arrow, an appropriate load is put on and fixed (in terms of weight parameters, a piece of tubular solder with a diameter of 3 mm and a length of 5 mm is perfect). It is necessary to ensure that there is a distance of at least 1.5 mm between the scale and the weight. We limit the edges of the scale with dampers made of soft foam rubber (5x5x5 mm), after which we again glue the body of the microammeter into one whole.
Below is the wiring diagram of the oscillation sensor:
It is quite clear that B1, in this case, is an M476 / 1 microammeter, and the polarity of its connection does not matter much. The KR140UD1208 opamp is used as the main signal amplifier induced in the microammeter frame. With slight fluctuations and the output voltage of the operational amplifier reaches a level sufficient to trigger the logic element D2.3, a first-level alarm is generated (there is no signal on D2.1 due to the voltage drop across the diodes VD1 and VD2). The second-level alarm signal is generated when the car body sways strongly, when conditions are created for the operation of element D2.1. In the role of assembly D2, you can use the K176LA7 chip. Resistor R2 is used to adjust the sensitivity of the sensor. Switch S1 allows the sensor to be used in security alarms with both normally open and normally closed contacts.
This home-made car alarm has been successfully operated on a VAZ 21051 car for a long time. It provides monitoring of windows, wheels, doors and hood and trunk lids. The car alarm is turned on using a button located in the passenger compartment, and turned off using a remote switch made in the form of a key fob for the ignition key.
The range of this design without an external antenna is only 50 meters, but with an external antenna it reaches 1.5 kilometers. The car alarm circuit is implemented on three modules: a rolling sensor, an electronic modulator based on transistors VT2, VT3 and a high-frequency FM generator. In standby mode, the circuit operates as follows: the rolling sensor contacts are not closed and battery power is supplied only to the high frequency generator.
The FM radio receiver is located at an acceptable distance and is tuned to the operating frequency of the burglar alarm generator, the disappearance of noise in the receiver is considered an indirect guideline for correct tuning.
car alarm wiring diagram
If the SA1 security sensor is triggered, power is supplied through its contacts to the modulator, which is nothing more than a multivibrator. It begins to generate low-frequency oscillations, which, through the resistance R5, enter the input of the high-frequency generator and modulate the high-frequency signal. As a result, a sharp intermittent alarm signal appears in the dynamics of the radio receiver. The carrier frequency of the transmitter is set by the frequency of the Q1 resonator and tuned to the standard VHF 64 - 75 MHz or FM 88 - 108 MHz band, which allows you to receive a signal on a conventional radio receiver
Communication between the key fob and the car alarm occurs with the help of infrared rays. In standby mode, the car alarm consumes no more than 10 mA. Within one minute after pressing the power button, the watchman does not respond to the state of the sensors. At this time, you can without haste close all doors, trunk and hood. After the expiration of this time, the device switches to standby mode and remains in this state until a signal from one or more sensors is received.
Car alarm with remote control circuit
The guard uses - one inertial sensor that reacts to the tilt of the body, which occurs when trying or removing the wheel; three piezoelectric sensors that respond to the touch of the tool to the windows and body, door opening sensors, which are used as door interior lighting switches. When a signal is received from the sensors, an intermittent sound signal immediately turns on, learns for about 45 seconds, and then the system switches back to standby mode. To turn off the watchman, you need to sequentially press two buttons on the key fob body.
In this way, two code words are sent even if the first word matches; if the second bishop does not match, the information about the match of the first is erased. This is how the simplest system of protection against scanning works. The circuit diagram is shown in the figure. As an inertial sensor, a pointer indicator from a tape recorder is used with an arrow B4 weighted and changed to the center of the scale. Oi is connected between the inputs of OYD 7. In this connection, maximum sensitivity is obtained. The op amp is connected according to the integrator circuit, from its output, the pulse that occurs when it is triggered (by moving the arrow as a result of the tilt of the body) is fed to the logic device on the D8-D9 microcircuits.
Piezoelectric “sensors are made from heads from old monophonic EPUs of the 111-EPU38 type or others, stereophonic ones can be used, but they are larger and less reliable. The signals from these sensors through the trigger level controllers B29 - R31 are fed to a two-stage signal amplifier 34 to VT8 and VT9, from it to a rectifier on VD21 hVD 22 and then to a DC amplifier on VT11 from the collector of which the pulse is fed to the logical device. The cascade on VT1O blocks the rectifier, and thus eliminates the possibility of the watchman looping from the sound signal.
Information from the door switches enters the logic device through a transient stage on VT12, which eliminates the failure of the microcircuit due to the supply of an unacceptably high level or static discharge to its input. The delay circuit for switching to standby mode after switching on is performed on D9.2 and D48C21. After switching on, the level at the output of this element is zero and remains at zero until C21 is charged. At this time, the pulses from the output D9.1 can not change the status of the output D9.2. The single vibrator on D9.3 and DV.4 determines the duration of the sound signal, the multivibrator on D8.2 and D8.3 interrupts the sound signal with a frequency of 1 Hz.
The remote shutdown circuit is made on the basis of the remote control circuit for color TVs of the USST type. The key fob is made on the D1 chip, which is used in control system transmitters. To set the code, the switching commands of 16 programs are used, two of them are used, in this case the 4th and 11th.
To turn off the alarm, first press K1, and then release it and press K2. The circuit of the photodetector on transistors VT3-VT7 does not differ from the similar circuit USCT. From its output, a serial pulse signal is fed to the D2 chip, which converts it into parallel, corresponding to the number of the included command. The binary code from the D2 output is converted to a decimal decoder on the D4 and D5 chip.
To the output of which is connected a diode matrix on VD4-VD17 that recognizes the code. The logic device is powered on and off in a cascade on VT15 and VT16, controlled by triggers on the D6 chip, when the short circuit is pressed, power is supplied to the circuit for a short time, the SI is charged and, with its charging current, sets the triggers on D6 to a state in which the output of the explosive. Z, a logical zero is formed, a unit enters the VT16 base and the VT15 transistor opens, bypassing the short circuit button.
With the correct supply of the first code word, a unit is received at the input "1" D6.1 and the trigger switches to the opposite position, releasing the trigger D6.3 and D6.4. Now it is enough to correctly apply the second word and the trigger to D6.2 and DG.4 switches to the opposite position and turns off the power to the device Each time an incorrect code is dialed, a signal with a level of one from the diodes VD4-VD17 goes to pin 6 of D6.2 and sets the triggers to the position corresponding to pressing the short circuit. has an on-board network with a nominal voltage of 12 volts, the missing voltage of 6 volts is generated by a generator on a chip D3.1-D3.4 This is a multivibrator with a frequency of 1 kilohertz and an ion output to which a rectifier is connected to VD18VD19 with a stabilizer to VD20.
Structurally, the watchman is made in the form of three blocks of a remote switch, a photodetector and the main unit. There can be more sensors, you can increase the number of piezoceramic sensors by turning on several sensors in parallel, you can introduce additional contact sensors that work for a short to ground by turning them on in parallel and turning the diode to the junction point R47 and VD23. In the device, one piezoelectric sensor was mounted directly in the body of the main unit. Its corundum needle was in contact with the bolt, the head of which protruded from the bottom of the body of the main bolt.
When installing the main unit, this cap is firmly attached to the metal niche of the front wheel. When hitting the body in any place or when the wrench touches the wheel nut, acoustic vibrations propagate through the body and reach this sensor. Two other sensors are placed outside the body of the main unit and their needles are in contact with the front and rear windows from the passenger compartment. The position of the inertial sensor in the housing is chosen so that when the housing is installed, the arrow of the former microammeter hangs vertically down, and the plane of its movement passes from one front wheel to the opposite rear wheel (from the left front to the right rear and vice versa).
The scheme can be significantly simplified if you abandon the remote switch and use a reed switch located in a secret place to turn it off, for example, near the external rear-view mirror from the passenger compartment. The electronic key fob can be replaced with a permanent magnet. In this case, the reed switch is connected between pin 13 and the power supply D6, between the same pin and the common wire, turn on the p “zisyaor for 10 kΩ, and connect pin 8 of the same microcircuit to pin 6. Now to turn off the alarm, you need to bring the magnet to the reed switch.
It differs from similar devices in the minimum of parts used. For it, a contact sensor is used, which can be used as door switches for interior lighting.
Car alarm algorithm of work. Leaving the car, the guard is connected to a power source (car battery) with a toggle switch located in a secret place. After switching on, a time delay of about one minute follows. This time is needed to close the doors, hood and trunk (if contact sensors are installed there too). After this delay, the circuit enters standby mode. When the door is opened, the watchman goes into operating mode, there is a delay of 5 seconds, which is given to the owner to turn off the alarm from the inside using a hidden toggle switch, then, if the toggle switch is not turned off, it goes into alarm mode, during which an intermittent sound is heard for 20 seconds from the car signal. After that, the watchman goes into standby mode.
car alarm circuit
When the watchdog is turned on, the capacitor C4 starts charging through the resistor R5. In this case, zero is supplied to the input of element D1.5 through diode D4, and the multivibrator on D1.5 and D1.6 is blocked. After charging C4 (and it takes 1 minute), a unit arrives at the cathode D4 and the zero flow to D1.5 stops. When the contacts of the sensor connected to Clem "D" are closed, the input of the one-shot to D1.3 and D1.4 is zero through D2.
As a result, a unit appears at the output of the single vibrator at pin 6 of the microcircuit, which, through the delay circuit, enters the cathode of the DZ diode, and it allows the multivibrator to work on D1.5 and 01.6. The R4 C3 circuit generates a delay of 5 seconds. Rectangular pulses with a frequency of 1 Hz from the output of the multivibrator are fed to the key on transistors T1 and T2, in the collector circuit of which the car signal relay winding is turned on. It is impossible to use this watchman in a car with a spicy signal (without a relay), for this you need to assemble the key according to the scheme with a thyristor, or install a relay from another car.
The sounding time of the signal depends on the circuit R3 C2, and after this time the circuit goes into standby mode. When used as a door switch sensor using CMOS microcircuits, it is possible for the microcircuit to fail due to the supply voltage to its input at a time when this voltage is not supplied to the power outputs. This situation arises due to the possibility of on-board voltage entering pin 1 of the microcircuit when the watchman is turned off. To eliminate this effect, a circuit of diode D1 and resistors R1, R2, R7 is used. When the watchdog power is turned off, the high resistance of the silicon diode connected in the opposite direction and the relatively low resistance of the resistors Rl R7 and R2 connected in parallel create a divider that lowers the voltage at pin 1 of the microcircuit to a safe value.
Diode D6 serves to protect against incorrect connection to the power source. Instead of the K564LN2 chip, you can use the K561LN2. The KT315 transistor can be replaced with KT342, KT3102 and even KT815, T2 can be KT817 or KT819, the use of KT801 and KT807 is not excluded. The capacitances of all capacitors may differ within certain limits, even several times, however, this will change the time intervals selected in this circuit, but they can be corrected by selecting the appropriate resistors.
It is desirable to use capacitors with low leakage currents, this is especially important for C 4 and C2, which, with a significant capacity, are paired with high-resistance resistors. In this case, the leakage current may make it impossible for the watchman to work. The watchman is mounted in a miniature plastic case from children's counting sticks and filled with epoxy to prevent dampness. It is located in an inconspicuous place under the dashboard, the toggle switch is also located there. The watchman can work with other sensors, it is important that when triggered, their output would be zero or negative pulse.
The main advantage of the car alarm circuit is that it does not require the installation of sensors for its operation and in the simplest version it is a small box to which you need to connect a 9-14V power supply and place it in a protected facility. In this case, the watchman will respond to any mechanical impact on the protected object, including blows, rattles, tool touches, etc.
The schematic diagram of the device is shown in the figure below. The sensor used here is a condenser microphone with a built-in Ml amplifier. From its output, the signal enters through the sensitivity controller 12 to a two-stage ultrasonic frequency converter on transistors T4, T5. From the output of the amplifier, the signal is fed to a diode rectifier on diodes D1 and D2 and to a transistor switch on T1. As a result, in standby mode on the collector T1 is one, and in the presence of an acoustic signal it is zero.
Car alarm circuit with radio channel
Actually, the logical security device of the car alarm is assembled on Dl and D2 chips. The pulse from the collector T1 is fed to the blocking shaper on the elements D1.1 and D1.2. From its output, a negative pulse is fed to element D1.3. The function of this element is to create a delay for switching on the standby mode after turning on the power within 20-30 seconds. This delay is needed to close the object's doors. When the power is turned on, the capacitor C2 is charged and its charging current blocks the passage of the pulse through D1.3.
The charging time of the capacitor is determined by the value of R3, and after it expires, zero is set at pin 8 D1.3. When the microphone sensor is triggered, a positive pulse from the output of this element is fed to the input of a single vibrator at C2.2 and D2.1. At the output of which a positive pulse is formed, lasting 15 seconds. This pulse through R9 goes to the transistor key T7, which supplies power to a single-stage VHF FM transmitter on the transistor T6, it has a power of 20 mW and operates in the VHF broadcasting range. When receiving on a radio receiver with a sensitivity of 10 microvolts, it provides a range within visibility - about 150 meters. This is enough to receive a signal on the ninth floor of the house from a car parked in the yard.
Through D4, the single vibrator allows the modulating multivibrator to work on D2.3 and D2.4. From its output, the signal goes to the D5 varicap, which is included in the transmitter circuit. At the same time, this signal is fed to the key on transistors T2 and T3, to which, during a major installation, an audio signal relay is connected. To prevent the loop-vanin of the watchman, the unit from the output of the one-shot to D2.1 HD2.2 is fed through R2 to the capacitor C1, which charges and closes the element D1.1, excluding the passage of a pulse from T1 through it.
At the end of the time specified by the R8 C5 circuit, the signaling stops, the watchman goes into standby mode, but not immediately, for some time, within one or two seconds, it takes C1 to discharge through R2, this is necessary to completely eliminate looping, which may, for example, occur due to contact break delay of the horn relay, and for another reason. When overhauling, a switch is used on the relay P1 and the reed switch Gr1. Button KH1 is used to turn on the watchman. When you press it, voltage is supplied to the circuit and the relay, which duplicates the button with its contacts, and is in this state until the relay is turned off by the action of the magnet on the reed switch, then its contacts will open and the watchman will be turned off.
With a major installation, it makes sense to fix the metal case of the microphone on some metal part of the body, in which case the microphone will not respond to extraneous noise and the car alarm will be triggered in case of touch or impact (depending on the position of the R12 sensitivity regulator slider) on the body. When it rains, it is recommended to set a low sensitivity, otherwise it will work from the impact of drops. All elements can be of any type, the L1 coil does not have a frame, its diameter is 8 mm, it contains 6 turns of PEV 0.8 wire. When setting the watchman, the transmitter is tuned to a free part of the range by squeezing or stretching the turns of the coil and adjusting C15.
By selecting R7 and R11, you need to set a voltage of 1.5V on the collectors of the corresponding transistors T4 and T5. If desired, all time delays and periods can be adjusted by selecting the values of the corresponding resistors.
A truly great variety of sensors used in car alarm kits. It is simply impossible to mention all the sensors and consider the principle of operation of each. Therefore, we will focus on those that are most often included in the protection systems of the initial, budgetary and medium levels.
Door opening sensors.
These devices are triggered if at least one of the car doors is opened in armed mode. Typically, sensors are connected in parallel - to one wire.
Sensors for opening the hood and trunk.
Actually, the same story as with the doors. Only the hood and trunk sensors differ in size and shape. In some entry-level car alarms, they are connected in parallel with door sensors. Since the system, due to its uniformity and low cost, does not provide for the presence of separate wires for the hood and trunk sensors.
By the way, the hood opening sensor should be installed in such a way that the wire coming from it cannot be approached from the outside. It should be said that this is how many cars were stolen. The criminals simply cut this wire with wire cutters.
Impact sensors.
There are two types: one and two-level, and depending on this they can have different sensitivities. A single-level shock sensor reacts predominantly to an impact force sufficient to, for example, break glass.
A two-level sensor is also triggered at a much lower impact force, but at the same time it sends only a warning signal to the system. In the event of a second cause for concern, this sensor already sends a signal to activate the siren and other danger alert functions. That is why it is called two-level.
It is worth noting that in car alarms of the initial, and sometimes budgetary level, the shock sensor is built into the central control unit, that is, it is located inside it. Therefore, in this case, the control unit should be installed in such a way that it has direct contact with the body.
And you do not need to put any gaskets and seals, because they will dampen the vibration of the body and the sensor simply will not notice it. Naturally, if the sensor comes separately from the central control unit, then it must also be attached directly to the metal of the car body. By the way, the ideal place for the shock sensor is the partition separating the engine compartment and the passenger compartment.
But if regular soundproofing interferes here, you can install it elsewhere. The main condition is metal. Therefore, in no case do not follow the popular belief that the shock sensor is best mounted on the plastic of the dashboard. This is complete nonsense!
Firstly, when the air temperature changes, especially in winter or hot summer, the plastic of the instrument panel and the metal of the car body react differently to such changes and the dimensions also change in different ways. In the case of metal, the process goes unnoticed, while plastic can be deformed, which causes cracking (for sure, they have paid attention to this more than once). This crackle for the shock sensor will be nothing more than a vibration, from which it will definitely work.
Secondly, if glass is broken in the car, the sensor, on the contrary, may remain silent, because the vibration from the impact will be transferred to the metal of the body, and it may not reach the instrument panel. If only the glass will fall into the interior.
Motion sensor (infrared sensor).
Once immensely popular device. Today, it’s just a useless “gadget” of cheap car alarms, which is often just annoying. The motion sensor is a small cylinder with a hole and some kind of lens on one side. Install it, as a rule, on the front pillars near the windshield. The sensor reacts to any changes in the coverage area.
Pay attention - to the changes, and not to what exactly creates them. Therefore, the main disadvantage of this device is endless false positives. Imagine, in the summer a fly flew into the interior of the car, which happens all the time. She will become the subject of attention of the motion sensor, which will react to her with the howl of a siren. And the owner of the car will puzzle over what's the matter.
In addition, with strong temperature changes, the motion sensor can also work without a reason. For example, in the summer day the car heats up, at night it starts to cool down, as well as in winter, the effect is the same. The metal cools down quickly, as a result of which certain changes occur in the sensor's sensitivity zone, and it certainly reacts to them. And even when dew falls, he cannot remain “indifferent”.
For these reasons, many modern manufacturers of security systems have abandoned motion sensors. But, I repeat, it is still present in some alarms, so be careful when choosing.
Volume sensor or microwave sensor.
This device has replaced the motion sensor described above and, unlike it, does not respond to flies, dew and temperature changes, therefore it is becoming increasingly popular with car alarm manufacturers. You can also adjust the zone of its sensitivity.
And volume sensors are multi-zone (or multi-level). Most often there are two-level devices. They, like two-level shock sensors, have one signal as a warning, and the second causes the warning system to work.
Depending on the principle of operation of the alarm, on its manufacturer, and even on the imagination of the installer, several volume sensors are sometimes installed at once - not only in the passenger compartment, but also under the hood and in the trunk. They are predominantly one level.
But it also happens that their only signal is intended to alert a separate alert sensor, which, depending on the settings, after a certain number of warning signals, will work and activate the alert system.
But this is not a cheap pleasure, therefore, when installing alarms of a budget and medium level, they mainly use one two-level volume sensor, which, by the way, often has to be purchased in addition to the system, because it is not included in its kit.
In entry-level systems, it is almost never used, since in the manufacture of such products the whole process is aimed at reducing its cost, and not at improving quality. Only in rare cases in cheap systems does the manufacturer provide a separate connector for the volume sensor.
By the way, despite the undeniable advantages over the shock sensor, the volume sensor has some disadvantages. It would be strange if they weren't. First, it is, of course, a high price. Secondly, in the case of a decrease in air temperature, the sensitivity of the volume sensor increases, which complicates its correct adjustment.
For this very reason, the probability of false positives is high. Thirdly, during heavy rain, when water flows over the glass, the sensor reacts to it and works. As for the installation of the volume sensor, its place is next to the central dome light.
But often it ends up in completely different places - under the console near the parking brake lever, under the dashboard, or somewhere else. After all, to install it where it should be, you need to try: remove the upholstery of the ceiling, which is very difficult to do, because you often have to remove the glass.
Therefore, the device ends up where, in principle, it is not able to work correctly, because it cannot be properly configured. After all, the dashboard, the console near the handbrake are made of plastic, which, as you know, is transparent to microwaves. And they are looking for metal objects on their way, which are a kind of “screen” for them.
Therefore, either follow where the volume sensor will be after installing the security system, or do not expect it to work correctly if the installers “attach” it under the seat, in the door, under the dashboard or under the console next to the handbrake.
Position sensor.
This device is used extremely rarely and only in cheap car alarms. But, despite this, it deserves to be remembered and told about. In one of the American films, the alarm was neutralized by lifting the car into the air using a helicopter. Just the job of the position sensor is to respond to such a manipulation.
That is, such a sensor is necessary if the criminals, for example, decided to remove the wheels from the car and changed its position for this - in a word, they jacked it up. In this case, the position sensor will work and the alarm will notify the owner of the car about the incident. It should be said that this sensor is rarely used for the reason that it costs a lot of money.
Vehicle roll sensor.
This once quite popular device was present in almost every security system without fail. But in our time, it does not enjoy special prestige among manufacturers, because the same functions are actually assigned to two-level shock sensors.
However, if a single-level shock sensor is installed in the system, then the rocking sensor will perfectly complement it. This combination of devices is convenient because the much more sensitive shock sensor can only be activated at night, and the rocking sensor can be kept on all the time. At the same time, even during the day, the rocking sensor will not allow you to remove wheels or other parts from the car, and also, in the event of an attempted theft, slightly raise the car in order to get to the right wires from below.
Glass break sensor.
This device is also called a glass break sensor. Of course, today this is already a somewhat outdated device, since the shock sensor also performs its functions.
In addition, the considered sensors are unreliable and unstable in operation. Judge for yourself, a device in the form of a microphone-type device reacts to the characteristic sound of breaking glass and can even work from the sound of a bottle broken near the car. If you lower the sensitivity threshold, the sensor will not work at all. Although, if properly adjusted, it may well be useful.
On-board network voltage drop sensor.
It is simply necessary to prevent the car from being stolen, as it reacts to any power surges on the on-board network, including when they try to introduce an extraneous device to turn off the alarm in the car's wiring.
Movement sensors.
This is one of the latest devices that are used in modern car security systems. The displacement sensor can be one and two-coordinate and controls the change in the position of the machine in space. Depending on the coordinate, respectively, in one - longitudinal - direction or in two - longitudinal and transverse.
This sensor is just perfect. It does not react to the vibrations of passing cars and other similar manifestations, so false alarms are simply excluded. The device operates exclusively for its intended purpose. Sends an alarm to the central control unit in response to any attempt to drag the car in tow or load it onto a tow truck.
Based on the book "How to avoid theft. Vehicle security systems.
N. G. Eremich.
If you are the owner of an expensive car, then most of all this article is not for you. And if you have a rather modest car and you want to protect your car at minimal cost (which is not at all proportional to the quality), then this description is for you.
The fact is that car alarm should not cost more than 5% of its market value, which for a used car is the amount for which you cannot buy a ready-made, more or less reliable, alarm system. The danger for a car without an alarm is not only in its theft, but also in the very penetration into the salon, theft of property, documents, etc., which is very common in the current conditions.
The damage may be small, or it may exceed the value of the car itself. In the traffic police, such cases are often not considered at all, since there is little evidence for them and they don’t initiate a case at all, stating that you yourself forgot your purse or documents somewhere, but you didn’t have any money at all. My friends had several similar cases, although the cars were equipped with purchased alarms.
But the fact is that scammers and thieves have long learned to bypass not expensive (although this is for someone), and rather monetary standard alarms. And it has become much easier to open (steal or rob) a car equipped with such a standard purchased alarm system. Now there are many different scanners with which an attacker reads your alarm code when you arm your car by giving a command over the radio from the key fob.
That's it, the "bad person" already has your code and he can easily both open the car and close it without attracting attention at all. Further, I think everything is clear to everyone. Therefore, having such an alarm, you significantly increase the potential theft or theft from the car, even compared to if you just locked it with a key, without the possibility of remotely opening the doors. And if we also take into account the human factor, the master who installs the alarm for you can naturally know how to turn it off, make a duplicate, etc.
Of course, most masters are decent people, but the facts show that if there is an opportunity, then someone will always take advantage of it. Data can be transferred to interested parties and "shoot" in a year or two after the installation of the alarm. It will be almost impossible to tie this into one whole, and even more so to prove it.
There are many more arguments not in favor of standard low and middle-class purchased car alarms, not to mention the costly part.
Consider the functions that a simple, inexpensive do-it-yourself car alarm should perform:
- The alarm should respond to penetration into the car, for example, using an IR motion sensor, or from standard light buttons that are triggered when a door or trunk is opened (the cheapest option, easy to implement, but nevertheless quite functional).
- An intrusion alarm should notify with a sound, a regular signal or an additional siren. This notification should last a certain time, for example two to five minutes, and then automatically turn off.
- After the alarm is triggered, the system should switch to the unauthorized entry mode - it should work repeatedly, block the engine start, etc.
- - The car alarm must consume low current, excluding the discharge of the battery (regular or additional) during the long-term parking of the car on guard.
- The mechanism of inclusion, transfer to the mode of protection and deactivation of the alarm system. In a simple case, a small delay (5-10s), after turning on the hidden toggle switch, while leaving the car and closing the door.
- Easy to manufacture and connect with low financial costs with maximum efficiency.
Such an alarm system will reliably protect even such a work as the Six-wheeled "Cossack Hammer"
Below is one of the most simple car alarm schemes that you can make yourself.
The car alarm combines an acoustic alarm that is triggered by the short circuit of the sensors (buttons for turning on the light of the doors and trunk) and when the ignition is turned on and blocks the engine from starting.
This scheme is suitable for installation on domestic cars equipped with a classic contact ignition system (VAZ, Moskvich, Volga, etc.) and any foreign ones with a similar contact ignition system. (Previously, all cars had a contact ignition system - they turned the key - the contacts closed), Installation is also possible in many new cars.
Homemade car alarm scheme quite simple and understandable to any novice radio amateur. All details are public and cost a penny. The connection to the electrical circuit of the car is also shown in the diagram. The bold line highlights the signaling unit itself, which is assembled in a small plastic case, selected from those available or can be purchased on the radio market - to your taste.
Everything outside the bold rectangle is the electrical equipment of your car, as well as other additional elements that are introduced into the car circuit (Sensors K2 and KZ, two relays P1 and P2, toggle switch 51).
Two types of contact sensors are used - regular interior lighting switches located in the car doors (they are connected in parallel, so the diagram shows one K1 sensor and one H1 lighting lamp), and specially installed sensors (door type) under the hood and trunk lid, if the trunk not equipped with a regular switch, similar to a door switch - so that when closed, their buttons are pressed and the contacts are open. When opening, the contacts must close.
As a sound signal source of the car alarm system, the regular signal of your favorite car or an installed purchased siren can be used. The signal is switched on using an additional electromagnetic relay of sufficient power (since the current passes through the signal coil), which must be installed in the engine compartment of the car - P1. The same P2 relay is used to block the ignition system. In principle, this relay can be placed in the box of the alarm itself. Its winding is connected in parallel with the winding P1 and when the alarm relay P2 is triggered, it shunts the capacitor C of the ignition system with its contacts, which makes it impossible to spark and start the engine.
The car alarm is activated using the micro-tumbler 51, which must be installed in a "secret place" inside the car (usually somewhere under the panel), known only to you and authorized persons. After turning on the power, the device will not respond to the status of all sensors for 15-20 seconds. This time is allotted for getting out of the car and closing the doors. After this time, the car alarm goes into armed mode.
To increase reliability, you can use an independent additional small battery, this is at will, desire and financial capabilities.
Even without an independent power source, such an alarm in modern conditions will be more reliable than a simple purchase with a remote control. About the cost is clear and so.
The system is economical. In standby mode, it consumes less than 0.7 mA, the trigger mode is 1.1 mA, and the current of the signal or siren is 0.2-0.5 A
Additionally, you can add an infrared motion sensor - purchased or if one was lying around on the farm.
If the sensor for 220V must be converted to 12V (8-20 Volts). A standard household motion sensor must be opened. The spherical part is removed by bending one support. The halves are fastened with latches.
Pull out the fee. The sensor is a passive IR receiver that responds to changes in the IR radiation that hits it. Typically, the motion sensor's field of view is 180 degrees.
Another simple car alarm circuit without chips
The circuit works on a similar principle, using the same sensors as in the previous case.
Short description:
SA2-SAn - intrusion sensors (door buttons, etc.). Diodes VD5-VDn are used to isolate the sensors if they are used for other purposes. If the sensors are only for signaling, diodes can be excluded.
The supply voltage supplied from any closed sensor, through R1 C1 is supplied to VD1. The R1 C1 circuit creates a short current pulse even if the sensor is left closed. Capacitor C2 prevents the alarm from triggering when the SA1 toggle switch is turned off.
The output key and multivibrator are assembled on the elements C4, R4, R5, VT2, K1. The duration of K1 being in the on position is determined by the selection of resistor R5 (you can install a variable resistor), and in the off position - R4. The overall pulse frequency is set by C4. This part of the circuit requires more careful tuning. Approximately around 2 Hz.
On elements C3, VD3, VD4, a node is assembled, which forms a delay in the alarm operation when the intrusion sensor is closed. This is necessary to delay the operation of the siren when the owner opens the car for 4-8 seconds to turn off the device (so as not to scare others :-)). The duration of the delay is set by the capacitor C3. The discharge of the capacitor when the power is turned off is provided by the resistor R3.
In this scheme, there is no node that would turn off the alarm after a while, this is the simplest option. If desired, such a node can be modified by slightly complicating the design, or you can use an autonomous time relay with periodic reset.
VD1 - any low-power thyristor, for example KU101. You just need to select C1 (increase if the alarm does not work when the sensor closes), R2 (decrease if it does not work) and C2 (increase if it works immediately when the circuit is turned on). Diodes - any low-power. Relay K1 - RES55A, or similar (selected according to the power of the switched current of the siren-signal). If you use a more powerful relay (more than 1A), then you will need to increase the capacitances of the capacitors C3 and C4 quite a lot (this will lead to an increase in the size of the device). Therefore, if you have a fairly powerful load, it is better to connect a powerful relay to the RES55A output. Transistors - also any, with the appropriate transition structure, and VT2 must withstand the relay turn-on current. SA1 - any small switch (tumbler).
To turn on the car alarm:
1. Turn on the SA1 toggle switch with the sensor closed (with the door open). In this position, the circuit will not turn on and can be indefinitely.
2. Close the door - the circuit switches to armed mode.
To turn off the car alarm:
1. Open the door (this will close the intrusion sensor).
2. Fast, within 8-10 seconds. disarm - turn off the SA1 toggle switch.
