Anti-theft alarm circuit for valuable home appliances

Anti-theft alarm for valuable home appliances This anti-theft alarm for valuable home appliances is small in size and loud in sound. Suitable for use in homes, hotels, institutions, etc. Working Principle: 　　　　　　　　　　　　The circuit principle is shown in Figure 1.

SCR, R1 and AN form a thyristor trigger switch circuit; IC1, R2, VT1, VT2 and BL form an analog siren circuit. Normally, AN is oppressed by household appliances, causing its two normally closed contacts to disconnect. The SCR is blocked without a trigger signal, and the alarm does not work. When the household appliance is lifted, the two AN contacts are automatically closed. The triggering end of the SCR obtains the triggering signal from the positive pole of the power supply through R1. The SCR is turned on, and IC1 is energized to work. The siren acoustic and electrical signal output by its output end is powered by VT1 and VT2. Amplify and push the speaker to make a loud alarm sound. At this time, even if the home appliance is put back to its original place or the AN is destroyed, the alarm sound cannot be stopped. Only when the owner opens the switch S, which is installed together with the alarm and is difficult for others to find, can the alarm be released. The component selection and production component list is shown in the table below. No. Name Model Quantity R1 Resistor 4.7K 1 R2 Resistor 240K 1 R3 Resistor 10K 1 VT1 Transistor 3DG6, 9014, etc. 1 VT2 Transistor 3AX81, 9012, etc. 1 SCR Unidirectional thyristor 3CT2K, BT169 0.1A/50V-1A/400V 1 IC Audio integrated circuit KD-9561 or other similar products 1 AN Micro switch normally closed type 1 BL Speaker 8Ω 1 S Power switch toggle switch 1 E Battery pack 4.5V 1 The alarm part can be installed in a small plastic box. Place it in a place where the alarm sound is easily heard (such as the duty room, etc.). Use a double-stranded thin wire to lead the AN to the place where the home appliances are placed, and place the AN cleverly on the desktop, countertop or TV cabinet, etc. to ensure that the AN can operate correctly.