What the motorist don't care how safer to protect your car from theft or intrusion by unauthorized persons? Here, as a rule, comes to the aid of the electronics. However, most electronic devices designed to protection of vehicles, often complex and expensive, besides for them often need insulated from the hull limit switches. All this limits the wide application of these "watchmen" by motorists.
We offer our readers several options for such devices, which are devoid of these shortcomings. Collect e "watchman" the description in the magazine can even inexperienced Amateurs.
I normally collected on two transistors (Fig. 1), first cascade VT1 limits the current flowing through the contact sensor system. This may be the end or mercury switches, sensors, etc.
Fig. 1. A schematic diagram of a security device
Transistor VТ2 collected time relay, providing turn-on delay "watchman". It gives you the opportunity to go to a-z vehicle after turning on security devices. The length of the delay within 6-12 set with the selection of the capacitance of the capacitor C1.
Relay K3 and the switch K4 are the key to the "watchman". The switch is hidden under some plastic (non-magnetic) part of the external cladding of the body the vehicle in a location known only to the driver.
Before you leave the car, the driver puts the switch in SА1 opposite in the diagram position, and the device is connected to the source power. Capacitor C1 begins to discharge through the resistor R3 and the transition "the base - emitter of the transistor VТ2, and opens. Relay K2 and your contact plates K2.1 breaks down the power key stage on VT1. At this time the driver leaves the car, closes the door. The condition of the sensors while does not affect the "watchman".
6-12 with the voltage on C1 is reduced to a level at which semiconductor triode VT2 is closed. The supply circuit of the first stage recovering, "watchman" goes into protection mode. As the consumption tone from the power source is very small, the electronic device may be a long time to work not only from the battery of the car, to and from three series - batteries connected 3336L.
If you now open, for example, the door closes limit switch mounted in the doorway. Base VT1 through the resistor R1 will be affected connected to GND, and the transistor opens. Relay K1 their contact system will block the sensor circuit and turn on the alarm. If after that, the door closed, the alarm will not stop. To disable it you can only switch SА1.
To get in the car, not broken dormancy others, the alarm on time off. Imperceptibly going to upset a small permanent magnet, disguised as some object (a piece of candy, a box of matches) the place where the reed switch. Under the action of magnetic fields of its contact the plate closes. Will relay K3, breaking the power circuit is a "caretaker" for by violating the contact K3.1 and smallareas by closing the contact K3.2. Now the driver can safely sit in the car and finally disable the alarm switch SА1.
In electronic security device in the first stage can also be applied transistors CTB (b, D, E, I, M, and the second CTS (G). As VD1 and VD2 it is also possible to use diodes D7, D226 with any letter index.
Resistors MLT-0.25, or MLT-0,5. Capacitor - C50-3, K50-6.
The device is equipped with relay RES-15 (passport PC4.591.003) and -22 (passport RF4.500.129). Can replace the RES-6 or RES-9 with a voltage actuation of 12 V. Reed switch may be of any type (CAM-3 CAM-1, CAM-2A). Switch - P2K.
Note that "watchmen" will work in conditions of high vibration, dust, humidity. Therefore, the mounting must be rigid, soldering reliable. Such requirements provides a so-called printed wiring (Fig. 2).
Fig. 2. Circuit security device location details
After Assembly and inspection of the patrol device installed radioelements epoxy glue to the Board. When the glue has hardened, with charge both sides coated with a transparent varnish, let dry, and then put into the body suitable sizes to suit turnips K1, K3, which are fixed inside the housing with through corners. "Watchman", get in the car, hiding in a secluded .
If the value of the current flowing through the sensors, do not impose hard requirements, the transistor VT1 (Fig. 1) in the circuit of the detector can be excluded (Fig. 3).
Fig. 3. A schematic diagram of a simplified version of the "watchman"
The mounting plate is a simpler version of a normally - on figure 4.
Fig. 4. Circuit Board simplified "watchman" with the circuit arrangement of parts
When using a "caretaker" for the protection of spaces, such as garages, cottages, and so D., you may need to increase the delay on the device In up to 1 minute. this case, the time relay is recommended to collect on a composite transistor (Fig. 5) having a high input impedance. Therefore, the discharge current capacitor C1 is significantly reduced as compared with the first scheme (Fig. 1), and the discharge time is increased accordingly. The duration of the hold the inclusion of "watchman" (Fig. 5) depends on the capacitance C1 and the resistance of the resistor R4.
Fig. 5. Schematic diagram of watchdog device with a timer on the composite transistor.
Due to the large scatter of the parameters of the transistors of the exact values of C1 and R4 in each case selected empirically. Maximum capacity C1 should not exceed 500 microfarads and the resistance R4 may be in the range of 30-100 ohms. Sometimes it happens that the current flowing through the transition collector - emitter VT2, it is sufficient for opening transistor VT3. In this case, in the collector circuit of transistor VT2 include resistor 1-2 ohms. If it is not enough, through resistor 20-50 ohms VT2 base connected to the common wire.
Circuit Board watchdog device with a timer on composite the transistor is presented in figure 6.
Fig. 6. Circuit Board watchdog device arrangement details
It is often necessary to "watchmen" and worked on opening contact chain. The scheme of such security device is in figure 7.
Fig. 7. A schematic diagram of a universal "watchman"
From the first indicator it is characterized by the presence of the Executive cascade on the transistor VT2. At its base is always present a positive offset, sufficient to open the transistor. To because the resistance of the sensor, connected between the base and VT2 common wire is many times less than the value resistor R2, on the basis of a negative locking potential: the transistor is closed. If we now break the chain gauge, VT2 opens, will relay K2 and the contact K2.1 employs a cascade transistor VT1. When the need for additional device you can disable the switch SA1.
Email "watchman" with the additional device can guard glass car or window of the premises. For this purpose, windshield and rear window glue along the perimeter of the foil strips 5-8 mm wide and slim plug stranded wire to the terminal x2.
If the glass will break or are going to take the foil will be interrupted, turning signal alarm. As the sensor can be used and foil heater rear window.
When setting the alarm note that the car alarm current consumption about 6 A, and it cannot be switched by using small relays, used in "the lookout". So loose the contact plate relay K1 connected to the standard relay signal. If this relay in the car are cars, old ones), it installs additionally, using a relay from cars "Lada" or "Moskvich". Instead of the electromagnetic relay is better to apply the thyristor CU with any letter index, vklyuchav in the chain the gate electrode resistor 750 Ohm with power dissipation not less than 1 watt.
Circuit Board universal "guard" in figure 8.
Fig. 8. Circuit Board universal "watchman" arrangement elements
Author: A. Surkov