Security alarm system. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Security alarm system. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling

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I offer a simple burglar alarm system that is designed to draw attention to remote objects that are under the protection of a sentry (watchman) who does not have access to the object. Its difference from the previously published ones is that, despite the simplicity of the design, in addition to monitoring the state of the sensors, the system provides:

- automatic shutdown of the sound signal when the sensor is opened for more than 1 minute, allowing you to save battery power;

- digital display of the number of operations, which is convenient for registration when changing duty and monitoring the security of the facility;

- automatic switching on of the standby mode when the closed state of the sensor contacts is restored.

The object of protection can be a garage, a car, etc.

The device consists of a control circuit on IC DD1, a digital indication unit on DD3 and HL1, a siren on DD2 and VT2, and a 9 V voltage regulator on VT1. The siren is assembled according to the scheme described in [1].

(click to enlarge)

Operation of the device

After turning on the power with the hidden toggle switch S1, you need to leave the room and close the door. This closes the contacts of the door sensor SF1. You can use several sensors connected in series. Capacitor C1 is charging. The charge current C1, flowing through the resistor R1, creates a logic level "1" at the input of the element DD1.1. Therefore, at the output of the element DD1.1 -logical "0", at the output of DD1.2 -logical "1", and the siren does not work. The logic level "1" from the resistor R1 is fed to the input "R" of the counter of the display device (pin 5 of the IC DD3) and sets it to zero. The indicator shows the number 0. The charge time for C1 is about 20 s. At this time, you can open and close the contacts of the door sensor - the siren will not work, and the indicator will remain in the "zero" state.

After charging C2, the system goes into standby mode. At the input of DD1.1 is a logical "0", it also goes to pin 5 of DD3, allowing the counter to work. The output DD1.1 - logical "1". If the sensor contacts are closed, logical "1.2" remains at the output of DD1, and the siren does not work. When opening the object, it is necessary to turn off the system with the toggle switch S1. If this is not done, then approximately 5 s after the opening of SF1 (charge time C2), a logic level "1.2" will appear at the output of DD0, a logic level "1.3" will appear at the output of DD1, which is fed to pins 12 and 13 of DD1.4 .13. At pin 1.4 DD1, the logic level "3" is valid only during the charge of C1, which is approximately 1.4 minute. During this time, the DD0 output has a logical "1" level, which turns on the siren. The system will also work if the SF1.2 sensor is not closed during arming. This allows you to monitor the status of the sensor. From the output of DD0, the logic level "3" is fed to the input "C" of the counter DD1 and switches it. "1" is displayed on the HL1 indicator. After 3 min. C13 is charging, and a logic level "1.4" is applied to pin 0 of DD1.4, which switches DD1 to a single state, prohibiting the operation of the siren. When contacts SF2 are closed, capacitors C3 and C3 are discharged, and the system enters standby mode. The counter DD1 is triggered only during the opening of contacts SFXNUMX. The indicator shows the number of openings.

By including additional sensors between terminal 6 of DD1.2 and the connection point of SF1 and C2, it is possible to ensure that the system will operate instantly when they are opened and with a delay - when SF1 is opened.

The device uses MLT resistors and K53-1 capacitors. Since the system was developed to control an object guarded by a sentry, the display device was placed in a separate case and installed inside the object, with the possibility of visual control from the outside (to take indicator readings when transferring a shift). The connection cable from the alarm system to the display device has been

carefully disguised. Obviously, the use of this device allows not only to draw attention to the protected object, but also improves control over its protection.

In standby mode, the system consumes current, which is mainly determined by the operation of the indicator. When powered by a battery, it is advisable to turn on the indicator only for the duration of the control, connecting pins 3 and 8 of HL1 with a common wire of a remote button, thereby reducing the standby current to a minimum. In the alarm mode, the current consumption increases to 0,7 ... 0,8 A. Since this mode lasts about 1 minute with each operation, the car battery lasts for several months. In this system, the high stability of the time intervals specified by RC circuits is not important. Only the reliability of the circuit in various temperature conditions depends on the quality of the capacitors used.

Literature

1. M. Shustov. Personal security sirens. - Radio amateur, 1995, N3, S.18.

Author: O.Soldatov, Balakovo, Saratov region; Publication: N. Bolshakov, rf.atnn.ru

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