Smart Home Control System Based on Single Chip Microcomputer and CAN Bus

4 Design and implementation of smart home control system software

In order to make the program clear and readable and run at a high speed, this system software adopts a modular structure design, which consists of a main program and related subprograms (such as keyboard scanning subprogram, display subprogram, voice prompt subprogram, dial alarm subprogram, electrical control subprogram, etc.). The main program flow is shown in Figure 2.

Figure 2 Main program flow chart

The program mainly includes three modules: security alarm, building intercom and telephone remote control.

The main program works as follows: the system is initialized after power-on reset. After the initialization is completed, the system detects the alarm signal, building intercom call signal and incoming telephone call signal respectively. If there is a signal input, it enters the corresponding processing module. In the security alarm module, a delay program is set to eliminate jitter and false alarms. The delay program is mainly implemented by calling the keyboard scanning subroutine. If there is still an alarm after the delay is completed, the local alarm, the alarm to the central control room through the CAN bus and the dial-up telephone alarm are carried out in sequence, thereby realizing the function of multi-point alarm and minimizing the loss.

In the building intercom module, the call signal of the door phone is transmitted to the extension via the CAN bus. After the extension detects this signal, it connects the intercom ringing, and then determines whether to pick up the phone. If there is no off-hook signal, it will delay the judgment. When the resident picks up the phone, the microcontroller outputs a signal to control the control relay of the audio communication line to turn on, allowing the resident to talk with the caller.

During the call, the microcontroller determines whether the user is on-hook. If the user is on-hook, the microcontroller returns. If the user is not on-hook, the microcontroller calls the keyboard scanning subroutine to determine whether the unlock key is pressed. If the unlock key is pressed, the microcontroller remotely unlocks the door through the CAN bus and the door station. The working process of the telephone remote control program module is that when there is an incoming call, the microcontroller first detects whether the phone rings 4 times, then simulates picking up the phone, and then plays a recording prompting the user to enter the password. If the password is incorrect, the user simulates hanging up the phone. If the password is correct, the microcontroller plays a recording prompting the user to enter the serial number of the appliance to be controlled, and then detects the control signal returned, and calls the appliance control subroutine to control the switch of the household appliance, and simulates hanging up the phone after completion.

5 Conclusion

The smart home control system designed in this paper makes full use of the powerful control function of the single-chip microcomputer and the outstanding features of the CAN bus, such as flexibility, convenience, high reliability, high communication rate, low price, and easy networking. It integrates the relatively independent systems in the smart home and realizes functions such as building intercom, telephone remote control, and multi-point alarm. CAN technology is a new control network technology. Combined with the existing mature public telephone network, it will gradually show its unique advantages in the application of smart communities.

Abstract: Aiming at the problem that the smart home system has low integration and little connection between systems, this paper introduces a networking technology based on CAN bus with a single-chip microcomputer as the control core, and designs a smart home control system that can realize building intercom, telephone remote monitoring and multi-point alarm functions in combination with the public telephone network.

1 Introduction

Smart home emerged in Japan and Europe and the United States in the 1980s, and entered China in the late 1990s. With the development of the economy and the improvement of people's living standards, it has gradually been understood and accepted by the Chinese people. At present, there are many kinds of intelligent systems and products in China, but each system is independent of each other, with low integration and little connection with each other. For example, building intercom systems, security systems, household appliance automatic control systems, etc., each has its own terminal, and there is no unified intelligent control platform. For users, this situation increases the cost of use and the complexity of operation; for construction, it leads to repeated wiring. In view of this situation, this paper designs a single-chip microcomputer AT89C52 as the control core, using the original telephone network to integrate the building intercom, security alarm and telephone remote monitoring system to form a unified intelligent control platform, and connects with the door machine and the management machine through the CAN bus network, which can realize the functions of building intercom, telephone remote monitoring and alarm. The intelligent home control system. This system is simple to operate, does not require repeated wiring, and reduces the cost. It is a system that is truly suitable for smart homes.

2 Main components and functions of smart home control systems

(1) Building intercom system

The building intercom adopts a community networking system, and the intercom system is installed at the door of each residential unit and in the residents' homes to realize the functions of visitor identity verification and intercom with residents, as well as remote control unlocking by residents, thereby effectively preventing illegal persons from entering residential buildings.

(2) Home security system

The home security system has functions such as anti-theft, fire prevention, remote monitoring and alarm.

(3) Household appliance automatic control systems

The main function of the household appliance automatic control system is to control household appliances, lighting and other electrical equipment. The system can realize local centralized control of home lighting or household appliances, and can also remotely control home appliances through telephone when necessary to save energy.

3 Smart Home Control System Hardware Design and Implementation

The indoor extension system of the smart home control system is shown in Figure 1. The system is mainly composed of a single-chip microcomputer and its I/O port expansion part, a building intercom part, a security alarm part, a telephone remote monitoring part, a node part connected to the CAN bus, and a keyboard and display part.

Figure 1. Structure of indoor extension system of smart home control system

3.1 MCU and I/O port expansion

The single-chip microcomputer uses the powerful AT89C52 as the main controller, which is mainly used for signal acquisition, data processing, and output of control signals. It is the core of the entire control system. Since this system requires many I/O ports, the I/O ports provided by the single-chip microcomputer itself are not enough, so the chip 8255 is used to expand its I/O ports. Among them, the PA port of 8255 works in output mode and is used to control the switch of household appliances; the PB port works in input mode and is used to input the alarm signals of various alarm detectors; the PC port is used to expand the keyboard.