Design and implementation of indoor wireless monitoring and alarm system based on ARM9

With the rapid development of computer network technology, mobile communication technology, and multimedia technology, wireless monitoring systems are widely used in military, industrial, agricultural and other occasions due to their convenience, practicality, and easy installation. They have also entered people's daily lives, bringing convenient information services to people's lives. This paper designs and implements an indoor wireless monitoring and alarm system based on ARM9, which realizes the functions of indoor environmental information monitoring, smart home control, image information acquisition and storage, and real-time remote information interaction with users, and can alarm in emergency situations. It has broad application and development prospects in the fields of smart buildings, smart homes, agricultural greenhouses, and breeding.

1 Hardware Design
1.1 Overall System Architecture
The wireless monitoring and alarm system is based on ARM9 and mainly realizes indoor environmental information acquisition, smart home control, image information acquisition, remote wireless monitoring and alarm, etc. The overall architecture of the system is shown in Figure 1, which consists of 7 main modules. Among them, the indoor information acquisition module realizes the acquisition of indoor environmental information, which is completed by different sensors. The temperature and humidity sensor is used to collect indoor temperature and humidity, the infrared sensor detects whether someone breaks in, the smoke sensor detects whether there is a fire, and the gas sensor detects whether there is a gas leak. The indoor home control module controls the switch of home appliances according to the instructions sent back by the user's mobile phone or the indoor information collected. The CMOS camera is used to capture the indoor situation. When a thief breaks into the room, the headshot can be captured and sent to the mobile phone and stored in the SD card. The SD card is used to save the pictures taken by the camera and the historical information of the indoor environment status. The buzzer sounds when an abnormality occurs in the indoor environment, which can be used to wake up the user and also serve as a deterrent when thieves break in. The touch screen is used to display the human-computer interaction interface, configure the alarm system, observe the indoor status, view historical information, etc. The GPRS module can realize wireless monitoring. The user can query the indoor status and control the indoor home by sending text messages to the system. When an abnormality occurs indoors, the monitoring system will send remote alarm information and pictures to the user.

1.2 ARM9 core control module
The core control of the system is completed by Samsung's ARM9 processor S3C2440. S3C2440 is a high-performance 32-bit RISC microprocessor, using ARM920T core, 0.13μm CMOS standard macro unit and memory unit, and the main frequency can reach 400 MHz. The design uses the smallest system Micro2440 of Friendly Arm, which includes basic power supply circuit, reset circuit, standard JTAG debug port, user debug indicator, CPU and storage unit, etc. The storage unit includes 64 MB SDRAM, 64 MB NAND Flash and 2 MB NOR Flash. In addition, its U-shaped interface expands various common buses, LCD and CAMERA interfaces, GPIO, etc.
1.3 Indoor information acquisition module
The temperature and humidity sensor uses Sensirion's digital sensor SHT11, and uses CMOSens technology to integrate humidity sensitive elements, temperature measuring elements, 14-bit A/D and serial interface circuits. It has the advantages of fast response speed, strong anti-interference and high cost performance. The design uses the GPIO port to simulate the serial port protocol to read and write sensor data. The infrared detector uses the ZT-7225 with a detection distance of 10 m, powered by 12 V, and has a relay output. The gas sensor uses the MQ-4 sensor that is sensitive to methane and natural gas. As the gas concentration increases, its internal resistance decreases. The design circuit is shown in Figure 2, where the variable resistor can set different alarm thresholds, and the smoke sensor uses the MQ-2 that is sensitive to smoke. In the design, the outputs of the infrared, gas and smoke sensors are sent to the processor through an AND gate to generate an interrupt signal.

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1.4 Indoor home control module
The indoor home control module realizes the control of home appliances by the system or user. The design adopts AC solid-state relay to realize the control of weak current over strong current. AC solid-state relay has no contacts, good reliability, long life and easy use. The relay load voltage selected in this article is 24~380 V, control voltage 3~24 V, and control current 3~25 mA. The control principle of home appliances is shown in Figure 3. ARM outputs a high level through the GPIO port to turn on the power supply and outputs a low level to turn off the power supply.

1.5 CMOS camera module
The system processor uses S3C2440, which has a built-in CMOS camera interface. In the design, it is brought out through the interface. The interface pin assignment is shown in Figure 4. The camera uses the CAM130 camera module from Friendly Arm, which includes an adapter board and ZT130G2 camera.

1.6 GPRS module
GPRS network is a wireless network with wide coverage and perfect performance. It has fast communication speed, strong anti-interference ability, low communication bit error rate, and fully utilizes the existing mobile communication network without construction and operation costs. The monitoring system implemented by GPRS has high real-time performance, safety and reliability, and low communication cost. In this paper, Huawei EM310 module is used to implement GPRS communication. The working frequency band of EM310 is EGSM900/GSM1800, compatible with GSM/GPRS Phase2/2+ protocol, and supports a UART interface. The EM310 module in the design communicates with ARM9 through this interface. Its circuit principle is shown in Figure 5. The system can send text messages to users to report alarm information through this module, or receive user text message instructions to respond to user remote operations.

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2 Software Design
2.1 System Main Program The
embedded Linux operating system is a real-time multi-task embedded operating system with excellent performance, open source code, portability, curability, tailorability and preemptiveness. It is widely used in small and medium-sized control systems and has the characteristics of small footprint, high execution efficiency, good real-time performance and strong scalability. The system software design part includes three main parts: porting and tailoring of the embedded Linux operating system, system application development and design of graphical user interface using Qt/Embedded. The porting and tailoring of the embedded Linux operating system is mainly divided into five steps: building the Linux development environment and establishing a cross-compilation environment; configuring and compiling the bootloader; configuring and compiling the Linux kernel; and installing the Linux embedded operating system. After completing the above steps, the development of the application program on the embedded operating system begins, that is, the core control program of this system. The process is shown in Figure 6. When the program starts running, it first initializes the buffer and some variables inside the ARM9, then initializes the serial port, timer, interrupt and peripheral devices, and then reads whether there is instruction information sent by the customer in the SIM card. If there is an instruction, the user instruction is executed; otherwise, the program starts to collect data from various indoor sensors and controls the corresponding home appliances according to the collected data. If there is abnormal information such as smoke or high gas concentration, the GPRS module will send a text message alarm to the user; if the infrared sensor detects that there is someone in the room, the camera will be controlled to capture a frame of image and send it to the customer via MMS. In order to prevent the user from not seeing the information in time, the user's mobile phone will be called 30 seconds after the message is sent to remind them.

After the program design is completed, it is downloaded to ARM9 for running through cross compilation; in addition, this system also uses Qt/Embedded to design a good human-computer interaction interface, which can be used to set the control mode and alarm mode of home appliances, and can also manually set the home appliances to be turned on and off.
2.2 GPRS module subroutine
The GPRS module subroutine involves GPRS module initialization, SMS service center address setting, short message format setting, alarm frame/control frame/response frame information assembly and parsing, short MMS sending and receiving, and making calls, etc. The basic process is shown in Figure 7. If you need to send MMS, dial up the Internet through GPRS Modem, establish a link with the MMS gateway, then encapsulate the picture and text into the MMS data packet, and then submit the MMS data packet to the MMS gateway through the GPRS network, so as to realize the sending of MMS. Sending SMS and dialing are realized by a set of AT commands specifically for controlling the GPRS module. These commands usually start with "AT" and end with a carriage return. The main AT commands used by the system are as follows: module wake-up: "AT\r"; short message information format setting: "AT+CMGF=1\r"; SMS service center address setting: "AT+CSCA=\"+8613800250500\"\r"; - Nanjing SMS center number; short message reading: "AT+CMGL=\"ALL\"\r"; - read all short messages; short message sending: "AT+CMGS=\"15105187703\"\r"; - user number; make a call: "ATD15105187703;\r".

3 Conclusion In
the paper , ARM9 is used as the core controller, and a smart home wireless monitoring and alarm system is implemented through cameras, touch screens, peripheral sensors, GPIO pins and GPRS modules. It can not only monitor indoor temperature and humidity, smoke, and harmful gases, but also control home appliances and monitor indoor safety. When someone breaks in, the camera can take a picture of the intruder's head; in addition, the GPRS module can be used to realize the functions of wireless alarm and user remote control. The implementation process of the system is described from both hardware and software aspects. The system has a good human-computer interaction interface. The whole system
is low-cost, stable, fast in response and has a wide range of applications. It is not only suitable for homes and buildings, but also has broad development prospects in agriculture, breeding and other fields through certain transformations.