A residential combined alarm system architecture

With the improvement of living standards and housing conditions of urban and rural residents, people's demand for residential security facilities has become more and more urgent. Although there are many kinds of alarm devices for residential security produced at home and abroad, most of them are either unaffordable due to high prices (several thousand yuan) or dare not be used due to poor quality. There are almost no security alarm devices that truly meet the national conditions of my country and the needs of urban and rural residents in my country.

In view of this, based on an in-depth study of various types of alarm devices currently available at home and abroad, and targeting the actual conditions of urban and rural residential areas in my country, we have separated the relatively simple and inexpensive sensor signal detection part (sub-end controller) from the relatively complex and expensive control and management part (central controller) of the entire system based on the design concept of high energy and low price. The two communicate via convenient and reliable telephone lines, and a central controller controls and manages multiple front-end controllers. We have developed a comprehensive residential safety alarm system that adopts a hierarchical distributed interconnection topology.

System Structure

The structure of this security alarm system is shown in Figure 1. It consists of three parts: front-end controller, central controller and communication line.

The front-end controller is installed in residential buildings to monitor and control different types of sensors (such as infrared, harmful gases and vibration, etc.) in different parts of residential buildings. It also processes the data collected from each sensor. When an abnormal situation occurs, it establishes a connection with the central controller through the telephone line in the home and transmits the relevant information to the central controller. The front-end controller can also receive and execute various control commands with password marks transmitted through the telephone line. When executing such control commands, the front-end controller will perform password verification, and only control commands with the correct password will continue to be executed.

The central controller is installed in the duty room of a residential building or community. It can control and manage multiple front-end controllers at the same time, so its cost is also shared by multiple users. The central controller is mainly used to receive and process data information from the front-end controller. Once an alarm message is received, it will immediately inform the duty personnel through the display speaker and other equipment so that corresponding processing can be made in time. In addition to being able to receive and execute various control commands with password marks transmitted through the telephone line like the front-end controller, the central controller also has an Internet interface, which can be easily connected to the Internet. Therefore, users can use any computer with Internet access to use a common web browser to access and control the central controller remotely within their authority range at any place through the Internet.

How the system works

Front Controller

The front-end controller is mainly composed of five parts: sensor group, AT89C2051 single-chip microcomputer, DTMF transceiver chip MT8888, telephone interface and sound circuit. As shown in Figure 2, it has a very simple circuit structure, and the type and number of sensors in the sensor group can also be freely combined according to the user's implementation needs and economic strength. The front-end controller has two working states: automatic operation and controlled operation.

Automatic working status

When working, the single-chip computer detects each sensor in a fixed cycle. For each sensor, there is a corresponding status bit in the memory of the single-chip computer. When a sensor is detected to have an alarm output, the corresponding status bit is set to "1". According to the detection results of each cycle, the single-chip computer makes a comprehensive analysis and judgment. Once it is determined that a dangerous situation has occurred, the single-chip computer dials the central controller through the telephone interface through the DTMF transceiver chip MT8888 according to the pre-stored telephone number, and transmits the alarm information (location of the dangerous situation, type of dangerous situation) to the central controller in DTMF mode. Then turn on the microphone to transmit the on-site sound to the central controller through the telephone interface for the duty personnel to monitor. Because it has the function of telephone process tone detection and judgment, if the single-chip computer does not detect the dial tone before preparing to dial, it is considered that the telephone line is faulty or damaged by human beings. The single-chip computer can immediately turn on the on-site sound alarm circuit and sound an alarm; if the single-chip computer detects a busy tone after dialing, it will wait for 5 seconds and redial until it is dialed. [page]

Controlled working state

The front-end controller can receive and execute control commands transmitted through the telephone line. These control commands include:

a. Command. Through it, the central controller can regularly detect the working status of each front-end controller to confirm whether each front-end controller is in normal working condition, so as to eliminate hidden dangers in time.

b. Open and close commands. Through it, the central controller and residents can open or close a front-end controller or several sensor inputs in a front-end controller according to the situation.

The controlled working state is password protected. The above commands can only be executed after entering the correct password.

Central Controller

As shown in Figure 3, the central controller is mainly composed of 7 parts: AT89C52 microcontroller, DTMF transceiver chip MT8888, voice chip ISD1420, serial interface chip MAX232, telephone interface and sound circuit.

(1) Receive alarm information from the front-end controller

The alarm information transmitted from the front-end controller via the telephone network in DTMF mode is sent to the MT8888 chip via the telephone interface, which decodes it into a digital signal and inputs it into the AT89C52 microcontroller. The microcontroller then sends the location and type of danger information contained in the digital signal to the digital display for display. The microcontroller then starts the speech synthesis chip ISD1420, which sends a synthesized alarm voice through the sound circuit to notify the on-duty personnel.

(2) Monitoring and control of front-end controller

The central controller can monitor and control multiple front-end controllers: it can periodically cycle through each front-end controller under the operation of the on-duty personnel to confirm whether each front-end controller under its control is in normal working condition; it can also turn on or off a front-end controller or several sensor inputs of a front-end controller under the operation of the on-duty personnel.

(3) Accept remote telephone control

In addition to operating the central controller through the keyboard in the duty room, the duty personnel can also remotely control the central controller from a remote location. As long as the correct password is entered, the remote operation and control of the central controller can be completed through any audio telephone and the keyboard of the telephone under the voice prompt of the central controller.

(4) Internet access

The central controller uses emWare's EMIT (Embedded Micro Internetworking Technology) to connect to the Internet. EMIT is mainly composed of the device service software emMicro, the network protocol emNet, and the gateway software emGateway. EmMicro resides in the microcontroller, monitors various state variables pre-defined in the central controller, and transmits the results to emGateway via MAX232; at the same time, emMicro can also interpret emGateway's commands to modify or control various state variables in the central controller. The information exchange between EmMicro and emGateway follows the emNet network protocol. EmGateway is installed in the PC, which is the communication bridge between the central controller and the Internet. In addition to exchanging information with emMicro, it also establishes a connection with the Internet web browser. In this way, users can use any computer with Internet access to complete the access or control of the central controller through the linked control web page anywhere in the world.

(5) Central controller interconnection

Since this alarm system adopts a hierarchical interconnection topology, the reliability and scalability of the system are greatly enhanced. Multiple central controllers can be easily interconnected to form a larger-scale security alarm network.

in conclusion

Since the software and hardware resources of cheap single-chip computers are fully utilized in the development of this alarm system, the traditional hardware circuit functions are realized by software to the maximum extent under the premise of meeting the real-time requirements, which greatly reduces the number of electronic components used, making the entire hardware circuit very simple and compact. This not only improves the reliability of the entire hardware circuit, but also effectively reduces the hardware cost.

In addition, in the design of the system structure, the use of a hierarchical interconnection topology and the control method of regular self-inspection and mutual inspection during system operation is very beneficial to the maintenance and management of the entire system, ensuring the safe and reliable operation of the system; and because the front-end controller has a simple structure and low cost, the cost of the central controller is shared by multiple users, which greatly reduces the cost that each user needs to pay (the total cost for each user is only a few hundred yuan).