Analysis of the impact of reverse voltage on the input end of DC/DC module

Smart home systems are widely used, and their functions are becoming more and more intelligent and personalized. They have become a hot topic in the domestic technology field. The basic function of smart home is to establish a communication network in a community, provide necessary channels for the transmission of various information data, and control and monitor all home appliances and equipment through corresponding hardware and actuators. Smart home terminals are an important part of the community smart home system. They not only control the operation status of various electrical appliances in the home and the security monitoring in the home, but also can be centralized to a management or control center through the network. The center provides public information resources or provides centralized security monitoring for each household. Smart home terminals play a hub role in the entire smart home system. An important functional module of smart home terminals is the communication module. How to formulate and implement communication protocols suitable for different transmission characteristics is the difficulty and focus of the entire system development.

At present, the main form of lighting control is to manually control all lamps one by one, which is not only troublesome but also inefficient and does not meet the standards of modern comfortable life. Therefore, designing an intelligent lighting system that can conveniently control functions such as lights is not only of practical value, but also has broad market prospects. Intelligence is not a synonym for expensive and impractical, but convenient intelligent lighting control, which can control various lamps in different living areas and occasions. In this paper, the original fixed mechanical switch is changed into a wireless remote control switch by using ST series single chip microcomputer, and the wireless remote control technology is used to send signals. In this way, a wireless remote control combined with a controller can control the opening of indoor lamps, which is not only beautiful but also practical and very convenient to use.

1 Overall design of control system
This system consists of three parts: wireless transmission module, wireless receiving module and switch power supply control module. The system structure is shown in Figure 1.

The wireless transmission module is responsible for sending the on and off instructions for a certain load circuit, and the receiving module is responsible for receiving the instructions from the transmission module, and then handing the instructions to the processor of the switching power supply control module. After the processor parses the instructions, it controls the opening and closing of the relay of the switching power supply module, thereby achieving the purpose of intelligent control of the load power supply.
2 System Hardware Design
2.1 Design of Wireless Transmission Module
The transmission module is mainly composed of HS1527 wireless code chip, surface acoustic wave filter, indicator light and filter circuit, etc. The transmission module is operated as a remote control, and the circuit diagram is shown in Figure 2. When different buttons K are pressed, the code chip will send different codes through the antenna, and the codes are sent to the receiving module through the antenna. The receiving module will hand over the codes to the control module for parsing and processing. The power supply voltage of the transmission module is 12 V, which is powered by a battery.

2.2 Design of wireless receiving module
The wireless receiving module consists of two parts. The power supply part consists of LNK304DN and peripheral circuits. This circuit can convert 220 V AC voltage into 5 V DC voltage to power the processors of the receiving module and the control module respectively. The circuit diagram is shown in Figure 3.

The wireless receiving part is mainly composed of a superheterodyne receiving module consisting of a decoding chip SYN500R, a crystal oscillator and peripheral circuits. The receiving module is responsible for receiving the code from the sending module and then passing the code to the processor for processing. After the processor processes the signal, it amplifies the signal through an amplifier and then controls the opening and closing of the relay. The circuit diagram of the receiving part is shown in Figure 4.

2.3 Control module design
The control module is mainly composed of a processor microcontroller, relays and peripheral components to form a switching power supply. The con end is connected to the AC lighting power, AC-L and AC-N are connected to the AC live wire and neutral wire respectively, and the OUT end is connected to the load. This system can control multiple loads. In the experiment, the control module is connected to a relay to control one load. The control module circuit diagram is shown in Figure 5.

3 Software Design
The software design adopts a modular structure. The main program workflow software development adopts ST Visual Develop development environment and uses C language modular programming, which brings great convenience to system debugging.
After the microcontroller is powered on, each module is initialized, including clock initialization, port initialization and variable initialization. After the initialization is completed, the program enters the main loop and executes the remote control decoding program and the key judgment program. When no button is pressed and there is no remote control data, the remote control decoding program and the key judgment program are executed cyclically. When there is an operation, the program enters the mode judgment state, and the microcontroller stores the remote control key data in the internal EEPROM to achieve the purpose of not losing data when power is off. When a matching remote control button is pressed, the corresponding lamp is turned on or off. After the operation is completed, the program
enters the main loop again to execute the remote control decoding program and the key judgment program. The flow chart is shown in Figure 6.

4 Conclusion
This smart home control system was tested in the laboratory. The controller was connected to two 100 W lighting lamps as loads for preliminary debugging. Two relays controlled the two lamps respectively. The remote control was used to control the on and off of the two lamps. The signal reception was good within 20 m in the open space indoors. The experiment achieved the expected effect and provided a basis for the next step of research. The current smart home wireless remote control technology is still in the process of continuous development and improvement, and has also encountered some problems in practical applications. For example, due to the interference of current wireless network signals, transmission bandwidth and stability limitations, some higher-level functional applications such as high-quality moving image transmission are still difficult to achieve. However, with the gradual construction of China's communication network, these constraints will be broken, and home intelligence and wireless remote control technology will be further developed.