Design of invisible anti-theft net for balcony realized by single chip microcomputer

1 Introduction

The problem of anti-theft follows, which leaves a broad market for invisible anti-theft nets . At present, the commonly used invisible anti-theft nets on the domestic market are mainly domestic brands, and there are very few foreign brands. Most of them use infrared or microwave detection to directly alarm, and their false alarm rate is very high. This design uses comprehensive detection, through computer comparison and analysis, and then makes a judgment on whether to alarm, thereby reducing the false alarm rate.

2 Design Concept

The main function of this device is to prevent thieves from entering the house from the balcony and windowsill. When there are people in the house, thieves generally dare not come, so the device should not have an alarm action; when there is no one in the house or no one is active (the owner is sleeping), thieves may "take advantage of the opportunity to enter", and the device should be prepared at this time. If there are "outside visitors" on the balcony or windowsill, the alarm will be issued. This device also has a "strict prevention" function for users to choose. When the device is in "strict prevention", no matter whether there are people in the house or not, as long as there are "outside visitors" on the balcony or windowsill, the alarm will be issued.

3 System composition

As shown in Figure 1, the designed device mainly consists of three parts: an external probe, an internal probe and a processor. The external probe is a dual-element infrared curtain passive motion detector of model RK-308, which is used to detect whether there are "outsiders". One is installed on the balcony and windowsill that need to be monitored for monitoring. The internal probe is a dual-element infrared motion detector of model RK-110DT, which is used to understand whether there are people in the house, living room, bedroom, study and kitchen. The number and location of the internal probes are determined according to specific requirements. The processor is mainly composed of a single chip, which receives the signals of the internal and external probes for analysis and determines whether to alarm. The single chip microcomputer uses 8751 single chip microcomputer, whose internal resources include 4KEPROM, 128RAM, 2 16-bit timers, 5 interrupt sources, and 32-bit I/O lines, which are sufficient for this design.

Now suppose that the object to be monitored is a two-bedroom, one-living room house, which has a balcony and four windowsills (one each in the living room, main room, study, and kitchen). Because the windowsill and balcony of the living room are in the same position, it is necessary to monitor a balcony and three windowsills, a total of 4 points, and install an external probe at each of these 4 points. In addition, an internal probe is installed in the living room, main room, study, and kitchen. In the single-chip computer, we select P1 as the input port of the external probe signal and P2 as the input port of the internal probe signal. The external probe 1 (living room balcony) signal is input by P1.0, the external probe 2 (main room window) signal is input by P1.1, the external probe 3 (study window) signal is input by P1.2, and the external probe 4 (kitchen window) signal is input by P1.3; the internal probe 1 signal is input by P2.0, the internal probe 2 signal is input by P2.1, the internal probe 3 signal is input by P2.2, and the internal probe 4 signal is input by P2.3. The P3 port is the output port of the alarm signal. In order to clearly indicate the alarm point, we set up 4 alarm signal outputs for the 4 monitoring points: P3.0 outputs the balcony alarm signal, P3,1 outputs the main room window alarm signal, P3.2 outputs the study window alarm signal, and P3.3 outputs the kitchen window alarm signal. This allows users to know in time which location the alarm is.

4 System Software Design

As mentioned above, this system has two working states: "strict defense" and "intelligent defense". Here, a "state setting switch" is used to set whether the system is working in the "strict defense" or "intelligent defense" state. In "intelligent defense", as long as there are people in the house, the system will not "monitor and alarm" the balcony and windowsill; when there is no activity in the house for a "period of time", the system will start to "monitor and guard" the balcony and windowsill. The length of this "period of time" is set according to the user's sleeping, balcony activities and other life patterns. Assuming that "a period of time" is 5rain, then in the program we call the "5s delay subroutine" and let it repeat N=60 times. The value of N is set by three pairs of dip switches.

The specific procedure is shown in Figure 2.

5 Conclusion

The system has a simple structure, reliable operation and low price. The number of internal and external probes and the length of waiting time can be set according to the specific situation of the user. If the user needs, the alarm situation can be recorded by modifying the program so that the user can understand the situation.