What motorist don’t care how secure your vehicle against theft or intrusion by unauthorized persons? Here, as a rule, comes to the aid of electronics. However, most electronic devices designed for protection of vehicles, often complex and expensive; moreover, they often need isolated from the body of limit switches. This limits the wide application of such “watchmen” motorists.

We offer readers a number of variants of such devices, which are devoid of these shortcomings. Gather electronic “watchman” according to the description in the journal can even inexperienced hams.
At watchdog device, assembled on dcoh transistors (Fig. 1), VT1 is the first stage limits the current flowing through the contact sensor system. It can be the end or the mercury switches, sensors, roll, etc.
Transistor VT2 assembled the time relay, providing a delay of inclusion of “watchman”. It gives the opportunity to go to a-z car after you enable the security device. The delay in the range of 6-12 with a matching set of the capacitance of the capacitor C1.
Relay switch KZ and K4 are the key to the “watchman”. Reed switch hidden under some plastic (non-magnetic) part of the external cladding of the car body in a place known only to the driver.
Fig. 1. Schematic diagram of the security device.
Fig. 1. Schematic diagram of the security device.
Fig. 2. The mounting plate of the security device with the location details.
Fig. 2. The mounting plate of the security device with the location details.
Fig. 3. A schematic diagram of a simplified version of
Fig. 3. A schematic diagram of a simplified version of the “watchman.”
Fig. 4. The circuit Board is simplified
Fig. 4. The circuit Board is simplified “watchman” with the layout of the parts

Before leaving the car, the driver moves the switch ЅА1 in the opposite position according to the diagram, and the device is connected to the power source. The capacitor C1 begins to discharge through the resistor R3 and the transition “base — emitter” of transistor VT2 and opens. Relay K2 and its contact plates K2.1 disconnects the supply chain is a key cascade on VT1. At this time, the driver leaves the car, closes the door. The state of the sensors while not affecting the work of the “watchman”.
6-12 with the voltage on C1 is reduced to a level at which the semiconductor triode VT2 is closed. The supply circuit of the first cascade is restored, the “guard” goes into protection mode. As consumption tone from the power source is very small, the electronic device can continuously operate not only from the vehicle battery, to and from the three series-connected battery 3336L.
If you now open for example the door closed limit switch mounted in the door opening. The base of VT1 through a resistor R1 impact connected to the common wire, and the transistor opens. Relay K1’s contact system will block the sensor circuit and turn on the alarm. If after that to close the door, the alarm will not stop. To turn it off you can only switch ЅА1.
To login to the machine is not broken the peace of others, the alarm time is turned off. Imperceptibly knock down a small permanent magnet disguised as some object (a piece of candy, a matchbox) to the place where the reed switch. Under the influence of a magnetic field the contact plate closes. Tripped short-circuit, breaking the power circuit “guard” at the expense of contact K3.Smallareas 1 and by closing contact K3.2. Now the driver can safely get in the car and finally turn off the alarm switch ЅА1.
In the electronic security device in the first stage it is also possible to use transistors КТ501Б (b, D, E, AND M, and the second КТ50ЗБ (G). As VD1 and VD2 it is also possible to use diodes D7, D226 with any alphabetic index.
Resistors MLT-0,25 or MLT-0,5. Condenser — K50-3, K50-6.
The device used relay RES-15 (passport PC4.591.003) and RES-22 (passport RF4.500.129). The latter can be replaced by RES-or 6 RES-9 with a trigger voltage of 12 V Reed switch — of any type (CAM-3, CAM-1, CAM-2A). Switch — П2К.
Note that the “watchman” will work in conditions of excessive vibration, dust, humidity. Therefore, the installation needs to be tough, reliable soldering. Such requirements provides a so-called printed circuit (Fig. 2).
After Assembly and test the operation of the watchdog device installed PCB with epoxy glue to the Board. When the glue hardens, payment from both parties cover with a transparent varnish, dry, and then place it into the housing of suitable size with turnips K1, KZ, which are fastened inside the case with corners. “The watchman” install in the car, hiding in a secluded place.
If the value of the current flowing through the sensors, do not impose stringent requirements, transistor VT1 (Fig. 1) in the circuit of the alarm device can be excluded (Fig. 3). The circuit Board is a simplified version of the watchdog device in figure 4.
When you use “guard” for protection of premises, such as garages, cottages, etc., you may need to increase the delay device to 1 min. In this case, the time relay is recommended to collect the composite transistor (Fig. 5) having high input impedance. Therefore, the discharge current of the capacitor C1 is significantly reduced as compared with the first scheme (Fig. 1) and the discharge time increases accordingly. The duration of the delay of inclusion of “watchman” (Fig. 5) depends on capacitance of C1 and resistance of resistor R4. Due to the large dispersion of parameters of transistors of the exact values of C1 and R4 in each case are selected experimentally. The maximum capacity of C1 should not exceed 500 µf, and the resistance R4 may be in the range of 30-100 ohms. Sometimes it happens that the current flowing through the transition of “collector — emitter” VT2, is sufficient for opening the transistor VT3. In this case, in the collector circuit of transistor VT2 includes a resistor 1 is 2 ohms. If it is not enough, then a resistor of 20-50 ohms VT2 base connect a common wire.
Circuit Board guard device time relay transistor on a composite of ka are presented in figure 6.
Fig. 5. A schematic diagram of a guard device with a time relay on a composite transistor.
Fig. 5. A schematic diagram of a guard device with a time relay on a composite transistor.
Fig. 6. Circuit Board guard device with the layout of the parts
Fig. 6. Circuit Board guard device with the layout of the parts
P and c. 7. Schematic diagram of the universal
P and c. 7. Schematic diagram of the universal “guard”.
R and p. 8. Universal circuit Board
R and p. 8. Universal circuit Board “guard” with the layout of the elements.

It is often necessary to “guard” worked and ka open contact chain. The scheme of such a protection device ka figure 7. From the first alarm device, it is characterized by the presence of the Executive cascade on the VT2 transistor. At its base, always present a positive offset, dostatochnoe for opening the transistor. To since the sensor resistance is connected between the base of VT2 and the common wire, is much less than the value of the resistor R2, on the basis there is a negative locking potential: the transistor is closed. If you break the sensor circuit, VT2 opens, work relay K2 and contact K2.1 uses cascade ka transistor VT1. If necessary, additional device you can turn off the switch SA1.
Electronic “watchman” with an additional device can protect the car glass or Windows of the premises. On front and rear Windows glue on the perimeter of the strips of foil width of 5 — 8 mm and connect the thin stranded wire to socket x2.
If the glass will break or be removed, the foil will rupture, enabling the alarm. As a sensor you can use a foil heater of the rear window.
When installing the indicator note that the car alarm consumes a current of about 6 A, and it cannot be switched with a small relay that is used in “the lookout”. Therefore, loose contact plate relay K1 is connected to the standard relay. If such a relay is not in the car (in cars, old ones), set it in further, using relays from cars “Lada” or “Moskvich”. Is the solenoid better to use a thyristor КУ202 with any alphabetic index, vkluchau circuit of the control electrode resistor 750 Ohms with a power dissipation of at least 1 watt.
Universal circuit Board “guard” — the figure of 8.

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