Large range laser burglar alarm

As shown in the figure, it is a large-scale laser anti-theft alarm circuit. The core of the circuit is a phase-locked loop circuit composed of IC3 (LM567) and its peripheral resistor-capacitor components. When the signal input at the input terminal 3 is consistent with the phase (frequency) of its own oscillation signal, the output of its logic output terminal 8 is kept at a low level; when the input signal is out of phase with its oscillation signal, the output of its 8th pin is high. The circuit adopts an adjustment-free same-frequency working mode, using the oscillation signal of the phase-locked loop circuit itself (the operating frequency of the phase-locked loop circuit is determined by the parameters of the peripheral R8 and C8) as the modulation signal of the laser at the same time, so that the transceiver circuit works at the same oscillation frequency, and the working mode is simpler and more reliable. When the circuit is working, the oscillation signal output from the 5th pin of the phase-locked loop circuit IC3 is transmitted to VT1 through R5 for amplification, and then drives the laser to emit a laser beam carrying the modulation signal. After multiple reflections in the propagation path, the laser beam irradiates the photoelectric tube VT2 of the receiving part and is converted into an alternating electrical signal. The signal is coupled to pin 2 of the operational amplifier IC2 through R4 and C4, and is amplified by IC2 and transmitted to pin 3 of the phase-locked loop circuit IC3. Since the phase of this signal is exactly the same as the oscillation signal of the phase-locked loop circuit, after internal comparison and identification, the logic output terminal 8-pin outputs a low level, TV4 is cut off, TV3 is turned on, and the green light-emitting tube LED1 lights up; when someone invades the warning area, the laser beam emitted by the laser is blocked, the propagation path is interrupted, and the photoelectric tube TV2 cannot receive the signal in an instant. At this time, there is no signal input to the input end of the phase-locked loop circuit, and the logic output terminal 8-pin jumps to a high level, TV3 is cut off, TV4 is turned on, and the 2nd and 6th pins of IC4 become low levels. The monostable delay circuit composed of IC4 and others flips, and its 3rd pin outputs a high level, and the red light-emitting tube LED2 lights up; at the same time, VT5 is turned on, and the relay J1 is energized, connecting the alarm circuit-the bell RL and the red light bulb H send out an audible and visual alarm signal. The length of the alarm time is determined by the transient time of the monostable circuit, which is calculated according to the parameters noted in the figure, which is about 50s. Component selection: In the circuit, RL is a 220V AC bell; H is a 220V red light bulb, and multiple bulbs can be connected in parallel; J1 uses a 6V relay with a contact current greater than 2A. Most of the other components are commonly used and can be selected according to the marked parameters. To ensure reliable operation of the circuit, it is best to add a DC power supply to prevent the alarm circuit from malfunctioning when there is a problem with the mains.