Design of intelligent alarm system based on single chip microcomputer

　　This system is designed mainly to meet the needs of automatic dormitory alarm. The design goal is to realize voice alarm, time setting and display, light alarm and network alarm and other functions.

　　1 Design

　　1.1 Selection of main controller

　　The 16-bit single-chip microcomputer SPCE061A from Lingyang Company is used as the main controller. Since SPCE061A has built-in 2KB SRAM and 32KB memory FLASH, it can meet the requirements of this system for storing passwords and various data, and the CPU clock frequency is as high as 49.152MHz, which can ensure the rapid response. The built-in voice module further improves the friendliness of the system's human-machine interface.

　　1.2 Selection of remote monitoring solutions

　　Wireless communication is adopted. Wireless transceiver module NRF2401 is used for wireless communication. This communication method is not affected by the length of the line, the position of the master and slave stations can be set arbitrarily, and the layout is relatively flexible.

　　1.3 Selection of Valuables Detection Solution

　　The width of the door frame is generally 1~2m, and it is more convenient to use a radio frequency transceiver module. The transmitter is attached to the valuables, and the receiver is fixed at the door. When the valuables enter or leave, it can be recorded. The circuit structure of the transmitter and the receiver are relatively simple, small in size, and easy to carry.

　　1.4 System Overall Block Diagram

　　According to the above design ideas, the overall block diagram of the system is shown in Figure 1. The system consists of two major parts: the host computer and the slave computer. The host computer performs keyboard input, voice prompts, alarms, and records the entry and exit of people and items. The slave computer performs data collection work such as smoke detection, human infrared detection, valuables detection, and personnel entry and exit detection. The slave computer sends the detection signal to the host computer through the wireless transceiver module. The host computer processes the data and takes corresponding actions.

Figure 1 System overall block diagram

　　2 Theoretical analysis and calculation

　　2.1 Calculation of object detection circuit

　　Wireless transmission and reception are used to detect valuables. The communication distance is related to the transmission power, receiving sensitivity and working frequency. The communication frequency is 8MHz and the inductance is 47μH.

　　but:

　　2.2 Control Scheme Analysis

　　According to the requirements of the topic, in order to realize remote monitoring of dormitory security, a master-two-slave mode is used for simulation, in which the master station can search the slave station, display whether the slave station is online in real time, and receive, process, display, record and alarm information, and the slave station obtains and sends information. The master station can display the slave station information in real time, and store the alarm and valuables in and out information in the FLASH of the master station, eliminating the need for external storage chips, which can be easily read and displayed. The human body sensor is used to determine the number of people in the dormitory by counting the number of people entering and leaving the dormitory, and the door is locked. The internal clock of the single-chip microcomputer is used as the time reference, and the time is set through the keyboard to record the alarm time. The voice module inside the single-chip microcomputer is used to realize voice alarm, which is intuitive and practical. This control scheme makes full use of the on-chip resources of the single-chip microcomputer, uses few external devices, and is simple and practical.

　　2.3 Smoke Detection Module

　　The MQ-2 smoke sensor is used, which has the advantages of wide detection range, high sensitivity, fast response recovery, excellent stability, long life, etc. It can realize smoke detection with a simple driving circuit. The smoke sensor circuit is shown in Figure 2. When no smoke signal is detected, the comparator outputs a low level; when the sensor detects a smoke signal, the comparator outputs a 5V high level and the alarm is activated.

Figure 2 Smoke sensor structure diagram [page]

　　2.4 Human infrared detection module

　　The passive infrared human body sensor is composed of chip BISS0001, pyroelectric infrared sensor KBS-6B and a few external components. The addition of Fresnel lens greatly increases the detection range and satisfies the human body detection requirements. When someone passes through the pyroelectric sensor, the Vo port of BISS0001 outputs a positive pulse and the alarm is activated. The circuit structure is shown in Figure 3.

Figure 3 Structure of pyroelectric infrared sensor

　　2.5 Personnel entry and exit detection design

　　Two infrared photoelectric switches placed front and back are used to determine whether a person enters or leaves the dormitory by detecting the switch sequence. When someone leaves the dormitory, control signal 1 is set high first, and then control signal 2 is set high. By judging the timing sequence, it can be concluded that the person has gone out. The same applies when someone enters. The detection circuit is shown in Figure 4.

Figure 4 Personnel entry and exit detection circuit diagram

　　2.6 Valuables Detection Design

　　In order to meet the requirements of valuables detection, a single tuned loop resonant amplifier is placed in the card, the card is hung on the valuables, the card sends out a radio frequency signal, when it enters or leaves the dormitory, it resonates with the secondary coil, the load voltage changes, and the entry and exit of the person can be recorded by detecting the load. The circuit is shown in Figure 5.

Figure 5 Valuables detection circuit diagram

　　3 Programming

　　After the master station system is powered on, it is initialized and requires a password. If the password is entered correctly, fire, valuables, keyboards, etc. can be monitored and corresponding processing can be made according to the monitoring situation. After the slave station is powered on and initialized, it starts to monitor the status of each sensor and send data. The program flow is shown in Figure 6.

Figure 6 Main program flow chart

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　　Test data and analysis

　　4.1 Test Instrument

　　The test instruments and models are shown in Table 1.

Table 1 Test instruments and models

　　4.2 Test methods and test data

　　The test methods and test data are shown in Tables 2 to 5.

Table 2 Smoke sensor output voltage test

　　The test data in Table 2 show that the smoke sensor performs well.

Table 3 Personnel entry and exit test

　　The test data shown in Table 3 meets the design requirements.

Table 4 Pyroelectric infrared sensor test

　　The test data in Table 4 show that the pyroelectric infrared sensor works well.

Table 5 Safety status record test

　　The test results in Table 5 show that the smoke sensor and human pyroelectric infrared sensor can both alarm and record normally, and can remind to lock the door when no one is in the dormitory. The wireless network runs well, and the password unlocking is also successful. The entry and exit of people and valuables can also be recorded smoothly. The dormitory security status within a few days can be checked through the keyboard, and all information is displayed on the LCD, which is clear and intuitive.

　　5 Conclusion

　　Through testing, this system has achieved various design requirements well.

　　The main innovations are the addition of a voice alarm function, which is more practical; the addition of a slave station search function, which can display the working status of each slave station in real time; the addition of an unattended function, which can immediately issue an alarm when human activities are detected during a specific period of time; and the addition of a clock function, which can realize time setting and display.

References:

[1]. SPCE061A datasheet http://www.dzsc.com/datasheet/SPCE061A_153.html.
[2]. NRF2401 datasheet http://www.dzsc.com/datasheet/NRF2401_521030.html.
[3]. BISS0001 datasheet http://www.dzsc.com/datasheet/BISS0001_172329.html.