Simple burglar alarm for the village. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Safety and security
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The proposed device is designed to protect summer cottages and private estates in villages from the encroachment of lovers of easy money. This is nothing more than a security alarm panel for several cells, the number of which may be different. The device is simple and reliable, has an autonomous power supply (element with a voltage of 1,5 V). The current consumption in standby mode is 0,1 mA. The current consumed by the cell in the off state is 80 μA. In alarm mode, the remote control consumes 10 mA.
Winding wires are used as security lines: PEV-2, PETV, etc. small diameter 0,08 ... 0,15 mm, which pass along the perimeter of protected areas through bushes, fences, etc. The greater the number of lines divided into a section, the easier and faster it is to determine where the troublemaker is located.
The scheme of the device is shown in fig. 1. In the initial state, when the remote control is turned on and the security loop connected to terminals 1 and 2 of cell A1 is not broken, i.e. its resistance is close to zero, the base of transistor VT1 is connected through diode VD1 to the positive terminal of the battery and transistors VT1 , VT2 and VT3 are closed.
(click to enlarge)
If the integrity of the line is violated, transistors VT1, VT2 open. The voltage from the collector VT1 through the diode VD2 is applied to the base of the transistor VT3 and opens it. Transistor VT3 provides a start signal to the DA1 chip. When the sound generator is working, an increased voltage appears on the cathode of the VD3 diode, and since the transistor VT2 is already open, this leads to the HL1 LED turning on, which indicates the number of the triggered cell.
In the case when the cell does not need to be armed, it is enough to turn off the SA1 toggle switch. Now, no matter what state the line is in (broken or shorted), the LED will not light up and the audible alarm will not turn on.
For test simulation of a line break, the SB1 button is provided. The simulator simultaneously checks the operability of all cells included in the standby mode. When the contacts of the SB1 button are opened, the closing voltage is turned off on the basis of the transistor VT1 and similar transistors of the remaining cells. Thus, a break in the security loop line is simulated. After pressing the SB1 button, a beep will sound and the LEDs of the cells that are in standby mode will light up. When the button is released, the system will return to its original state. Turn off the remote control with a common switch SA2.
Chip DA1 - from a Chinese alarm clock. The location of the pins of this microcircuit is shown in Fig. 2.
Author: V.Polovinkin, Zheleznogorsk, Kursk region.
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