Laser detection anti-theft alarm circuit

The laser detection burglar alarm introduced here has the characteristics of simple circuit, easy production, and long monitoring range (.500~1200m)
. It can be used for anti-theft alarm in agriculture, forestry orchards, vegetable fields, fish ponds and other places.
    (1) Circuit composition and working principle The laser detection anti-theft alarm circuit consists of a power supply circuit, a laser monitoring circuit and an audio alarm circuit
, as shown in Figure 13-49. The power circuit consists of the step-down capacitor cl, the discharge resistor Rr, the rectifier diode VD1-VIX, the filter capacitor
c2, the current limiting resistor and the voltage stabilizing diode vs.
    The laser monitoring circuit is composed of laser, photoresistor RG, resistor and transistor VT1.
    ． _The
    sound alarm circuit is composed of alarm sound integrated circuit IC, resistor winder, transistor VT2 and speaker BL.
    After the AC 220V voltage is step-down by c], rectified by VD1~VD, filtered by cZ, current limited by wind and stabilized by vs, one channel provides
+4.5V working voltage for the laser, and the other channel supplies the sound alarm circuit.
    Normally, RG is irradiated by the laser emitted by the laser and is in a low-resistance state. VT1 is cut off because the base potential is extremely low, IC does not operate, and BL does not
sound.
    When someone or an object enters the warning area and blocks the laser path, RG becomes a high-resistance state, and the voltage drop at both ends increases, causing VT1 to saturate and conduct
. After the IC is powered on, the sound effect electrical signal output is amplified by VT2 and drives BL to emit Alarm sound (siren).
    If you think the alarm sound is too low, you can add a set of power amplifier circuits or use the 'IWH series high-loudness alarm and boost power amplifier block. If the warning distance
is far away, the laser and the laser receiving alarm circuit can be powered separately.