High-sensitivity and high-loudness burglar alarm circuit

As shown in the figure, this is a high-sensitivity and high-volume anti-theft alarm circuit. This alarm is suitable for orchard anti-theft alarm. It is very sensitive and loud, and has a strong deterrent effect on thieves. Even if there is no one in the orchard for a short time, there is no need to worry about the fruit being stolen, because the urgent alarm of "Catch the thief" will easily attract people's attention and scare away the thieves. This alarm uses a disconnection trigger method. Once triggered, it is useless even if the wire is connected again. The alarm will stop automatically after about two minutes. This circuit is easy to make, does not require debugging, has good effect, and does not consume electricity at ordinary times.

The working principle circuit is shown in the figure. SCR, R2, and L constitute a disconnection controllable trigger power switch, and L is the anti-theft line. Transistor VT and IC1 constitute a monostable delay trigger circuit of about 2 minutes. IC2 is a language "catch the thief" alarm circuit. Usually, K is closed, and when there is no theft, the alarm anti-theft line short-circuits the SCR control electrode trigger current to the ground, the SCR is cut off, the circuit does not work, and is in a guarding state. When the thief climbs over the wall and enters the garden, the SCR control electrode is turned on by the trigger current obtained by R2 due to the break of the wire L, and the working circuit is powered. Transistor VT is turned on, and the negative pulse signal triggers IC1's 2nd pin through C1, and then the 3rd pin outputs a high level. The 4.5v voltage stabilized by DW makes IC2 work, and sends out a "catch the thief" alarm signal. After this signal is coupled to IC3 for power amplification through C6, the speaker emits a loud alarm sound. When IC1 is triggered, C2 is charged through R5. After about 5 minutes, the 6th pin is high level, the 3rd pin outputs a low level, and the alarm circuit stops working. At this time, the indicator LED2 lights up, indicating that the alarm has worked once. At this time, turn off the power switch K, connect the anti-theft line, and then reclose the K circuit to enter the empty monitoring state. The light-emitting diode LED1 is used as a power indicator.

Component selection: IC1 is NE555 time base circuit, IC2 uses LQ6 voice integrated circuit chip, 1C3 uses TDA2003 power amplifier integrated circuit. Transistor β≥100. One-way thyristor SCR is 1A100V high-sensitivity trigger type. Light-emitting diode is Φ5mm high-brightness type, anti-theft wire uses enameled wire, and the length is based on the ability to surround the orchard. The power supply is a 12V battery.

During production and debugging, the printed circuit board is arranged according to the size of the selected components. When laying the anti-theft wire, first use bamboo nails to nail at an appropriate height on the surrounding walls at a spacing of 5m, then wrap the anti-theft wire around it and wrap it around the wall for a week, and connect the two ends to the circuit. In order to make the anti-theft wire easy to break, you can cut it in the middle of each section, and then connect it well. Don't connect it too firmly. It is better to make the joint disconnectable with a little pressure. But also prevent virtual connection, so as to avoid false alarm after the switch K is closed.