Security system for the house. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling
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We offer a security system for the house from inexpensive components.
Figure 1 shows a schematic diagram of the device.
(click to enlarge)
Security circuits marked as "Zone 1", "Zone 2° and "Entry/Exit" with normally closed alarm sensors (S4, S5, S7) in the form of switches, reed switches, etc.
Tamper Loop" (S6) - a circuit in the form of a wired or tape signaling loop, also normally closed.
The alarm (light, sound, etc.) of the security system is triggered when the circuit of any security circuit is broken. For example, if the circuit "Zone 1" is violated, then the input pin 2 of the OR element IC1 and through the resistor R1 is high, the transistor TR6 opens, the glow of the LED D5 indicates an alarm. At the same time, transistor TR5 will open and the waiting multivibrator IC5 will start. During the period of its operation, set by the potentiometer VR2, the contacts of the RLA relay will close.
The switching circuit, consisting of transistor TR5 and capacitor C8, is necessary, because if the sensor S4, connected to the OR element, turns out to be permanently open (for example, the wire of the window protection circuit is broken), then the alarm will sound indefinitely. The presence of resistor R16 allows capacitor C8 to discharge in a few seconds after the integrity of the zone circuit is restored, ensuring that the system is armed.
The three key switches S1...S3 can be of different types, but they must turn off when the contacts are closed, and they must turn on the system and start the output timer by opening.
On the prototype, the "lock" was a 36-socket Centronics receptacle, and the "key" was an appropriate plug with six jumper pins.
The time required to leave the guarded area is set using the waiting timer IC4. With the key switch S1 closed (the security system is disabled), there is a voltage of 2 V at pin 4 of IC1, so there is a high level at the output of the timer (pin Z). After inverting to 3C1c, it is fed to one of the inputs 2C1a (circuit I), the output of which is connected to the input of the trigger formed on 3C1a and 3CXNUMXb.
While the "Exit / Entry" zone is closed, pin 1 1C2a will be low. After violation of the "Exit / Entry" zone, the output of trigger Q (pin 4 1C3b) will go high. Capacitor C3 begins to charge, providing entry time, after 17 seconds, but pin 5 1C1a is set high. If the key is inserted during this time, then the IC5 alarm timer will be stopped. The exit timer is reset and the trigger is reset. Otherwise, the alarm sounds the same as before. Capacitor C4 provides a trigger reset when power is applied. LEDs D1 ... D4 provide indication of the status of the corresponding security circuit.
Figure 2 shows a diagram of a power supply for a security system, which provides for charging a lead acid battery.
(click to enlarge)
Author: D. Macuire, Ireland
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