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How to Make Burglar Alarm Circuit

This article will introduce the burglar alarm circuit and hope to help electronic enthusiasts.

Broken burglar alarm circuit

The ultra-low power disconnected burglar alarm is simple, easy to manufacture, low in cost, and low in static power consumption (only 8μA). It is very suitable for theft prevention in homes, warehouses, shops and farms.

Broken burglar alarm circuit
Broken burglar alarm circuit

The alarm circuit principle is very simple. BL is a high loudness speaker with built-in sound source, and VT is an N-channel MOS FET. Usually, the thin wire is wound around the object to be protected (or will be surrounded by the object to be protected). In the circuit, ab is short-circuited at two points, VT is cut off, and BL does not work. At this time, only the resistor R consumes some electric energy in the entire circuit (the quiescent current of the entire circuit is only 8 μA when the battery voltage is 12V).

When the thief stealing will be cut or broken by the thin wire on the protective object, ab is disconnected at two points, and the gate and source of the VT obtain voltage, so the VT is turned on, the BL is energized, and a loud alarm sound is continuously emitted. When the battery voltage is 12V, the alarm sound of this high-loud speaker can reach 120dB.

Burglar alarm circuit diagram

Burglar alarm circuit diagram
Burglar alarm circuit diagram

Electric car burglar alarm circuit

The transmitter transmitter section is powered by relay K and thyristor VS to control the transmitter circuitry. IC1 constitutes an alarm signal circuit. The transistor V and its peripheral components form a radio frequency oscillating circuit and emit an alarm signal.

Electric car burglar alarm circuit
Electric car burglar alarm circuit

In the waiting state, the switch S1 is turned on, and the SB1 is turned off (ie, the front lock is locked), K is in the released state, and the alarm transmitter does not work. When the front lock is turned on (ie, SB1 is turned on), VS is triggered to conduct, K is pulled, and the transmitter is turned on. After the SB1 is turned on, the K-2’s normally open point will self-lock, and only the S1 alarm can be turned off to end. When K is actuated, its normally closed contact K-1 is opened, and the engine ignition circuit is cut off.

The receiver circuit consists of the TDA7010 and the switching amplifiers TWH8778 and TWH68. When IC2 receives the alarm signal, the high level of its mutual pin is amplified by IC3 through IC4 and the alarm sound is released by TWH15. However, the stability of the frequency should be considered, because the 7010 itself does not have a frequency stabilization circuit, and it is necessary to perform more tests during operation, preferably using printed boards and chip components.

After parking the vehicle according to the above operation method, the alarm enters the alarm state. During the alarm period, whenever someone unlocks the front lock or moves the vehicle, the alarm will be triggered and the engine power will be cut off to prevent the vehicle from starting until the owner has rushed to insert the ignition key into the ignition lock. The alarm can be released only after the position is closed.

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