Security system of remote objects with digital indication. Free Technical Library article

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Security system of remote objects with digital indication

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

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The system described in the proposed article is designed to protect remote objects that are inaccessible to a watchman or sentry.

The object of protection can be a garage, a car, etc. In addition to monitoring the status of sensors, the system provides:

automatic shutdown of the sound signal when the sensor is triggered for more than one minute, which saves battery power;
digital display of the number of operations, which is convenient for their registration when changing duty, as well as for monitoring the object;
automatic setting of the standby mode when the closed state of the sensor contacts is restored.

The diagram of the device is shown in the figure.

Security system of remote objects with digital indication

(click to enlarge)

A control unit is assembled on the DD1 chip, a digital indication unit is assembled on the DD3 and HL1, and a siren is assembled on the DD2 chip and the VT2 transistor. The siren was assembled according to the scheme described in the article by M. Shustov "Sirens of Personal Security" in the journal "Radio Amateur", No. 8, 1995.

To arm the system, you need to turn on the power with the SA1 secret toggle switch, leave the room and close the door, while the contacts of the SF1 door sensor will close (several sensors connected in series can be used). The charging current of the capacitor C1, flowing through the resistor R1, creates a high-level voltage at the input of the element DD1.1. At its output - a low level, and at the output of DD1.2 - high. Therefore, the output of element DD1.4 will also be high and the siren will not work. The high level from the resistor R1 is fed to the input R of the counter-decoder DD3 and sets it to zero. The HL1 indicator shows the number "0". The charging time of the capacitor 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 the capacitor C1, the system goes into standby mode. At the input of DD1.1, a low level is set, which is fed to pin 5 of DD3, allowing the counter to work. At the output of DD1.1 - a high level, and if the contacts of the sensor SF1 are closed, the output of DD1.2 will be the same level: the siren does not work.

After opening the door (opening the contacts SF1), it is necessary to turn off the system with the toggle switch SA1. If this is not done, then after about 5 s (capacitor C2 charging time), a low level will appear at the output of element DD1.2, and a high level will appear at the output of DD1.3. From the output of the element DD1.2, a low level is fed to the input C of the counter DD3, and "1" is displayed on the HL1 indicator. At pin 13 DD1.4, a high level is present only during the charging of the capacitor C1.4, which is approximately equal to one minute. During this time, the output of the DD13 element is low, which allows the siren to work. After one minute, the SZ will be charged and a low level will appear at the output 1.4 of the DD1.4 element. A high level at the output of DD1 will disable the siren. The system will also work if, when it was armed, the SFXNUMX sensor was not closed, which allows you to control the state of the sensor.

When contacts SF1 are closed, capacitors C2 and C3 are discharged and the system enters standby mode. The DD1 counter is triggered only during the opening of the SF1 contacts, the HLXNUMX indicator displays the number of openings.

By including additional sensors between terminal b 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, 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 during the transfer of a shift. The connecting cable from the alarm system to the display device was carefully disguised.

In standby mode, the main part of the consumed energy is spent on the operation of the indicator. When the system is powered by a rechargeable battery, it is advisable to turn on the indicator only for the time of monitoring. To do this, you need to install a button that would close the connection point of pins 3 and 8 of the HL1 indicator with a common wire. In this way, the current consumption in standby mode can be reduced to a minimum. In alarm mode, the current increases to 0,7...0,8 A.

In the proposed device, the high stability of the time intervals specified by RC circuits does not matter. Only the reliability of the system in various temperature conditions depends on the quality of the capacitors used.

Author: O. Soldatov, Balakovo, Saratov region, Radio No. 10, 1998, p. 60,61.; Publication: cxem.net

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