Multi-channel laser anti-theft alarm circuit

As shown in the figure, it is a multi-channel laser anti-theft alarm circuit. VT1, VT2, RL1, RP1, R1, K, VD6 constitute a light-controlled switch. During the day, the photoresistor RL1 is in a low-impedance state under light, VT1 is saturated and turned on, VT2 is cut off, relay K is not energized, the normally open contact J is in a disconnected state, and the alarm circuit does not work; at night, RL1 becomes a high-impedance state, VT1 is cut off, VT2 is saturated and turned on, K is energized to make J close, the circuit supplies power to the whole machine, the red light-emitting diode LED is on, and the regulated 6V is stepped down by VD7, VD8, and VD9 to supply power to the subsequent circuits. The laser rod JB1, RL2, VT3, RP2, R3, and R4 constitute a laser transmitting and receiving network. When the alarm is in the standby state, the laser rod emits a red laser, which shines on the photoresistor RL2. RL2 is in a low-impedance state, and the base potential of VT3 is very low, providing a trigger current for the thyristor VS. VS is turned on, IC2 is energized to work, and the speaker sounds an alarm. The alarm can set up to 10 laser transmission and receiving networks at the same time, with the same circuit structure. C3 is an anti-interference capacitor. AN is a reset switch. When the power grid fails or the criminals cut off the power supply, the battery immediately supplies power to the whole machine, ensuring the reliability of the alarm device.

Component selection: IC1 is a voltage-stabilizing integrated circuit 7806, and an aluminum heat sink is required when used. IC2 is a KD-9561 four-sound chip, and this circuit is connected to the second sound selection terminal SEL2 (fire truck alarm sound). The laser source uses a red laser rod with a voltage of 4.5V and a power of <5mW. VT1, VT2, VT3, etc. use 9013, and β≥100 is required. All photoresistors are sealed. The larger the dark resistance and the smaller the light resistance, the better. The model is not limited. All resistors use (1/8)W carbon film resistors. T is a power transformer with a secondary voltage of 9V. The power must be above 8W. Try to use a high-quality transformer with a small no-load current and no heat when powered on for a long time without load. K is a 6V micro electromagnetic relay, such as 4099. This circuit uses its normally open contact. The speaker is 8Ω, 0.2W. E is 6 No. 1 batteries connected in series.