Research on multi-communication media information home appliance network controller

    Abstract: This paper provides a new home gateway based on multiple communication media and unified application layer protocols. The gateway can be used to control home appliances and other audio and video equipment. It is low-cost, requires no or few connecting lines, and has high reliability. It can perform data communication through power lines, telephone lines, Ethernet, wireless networks, etc. Users It can be controlled through an Internet browser or a telephone line PC; the control information flow from the Internet/Intranet can be received and converted into the universal RS232/RS485 protocol, so that most microcontrollers can process these data. The gateway also provides Bluetooth and USB interfaces, which can easily establish connections between users and home appliances without considering various underlying protocols, providing effective network solutions for home automation, distributed systems, robot control, etc.

    Keywords: Information appliances, home gateway, power line communication, Ethernet, consumer electronics bus

introduction

With the advancement of science and technology and the continuous improvement of production quality requirements, people's choice and use of home appliances have shifted from caring only about the individual functions of home appliances to pursuing the taste and convenience of control of home appliances. The development of information technology and network technology has made it possible for centralized control and remote control of household appliances and the home environment. The integration of information technology and home appliance control technology can realize the informatization and automation of family life to a greater extent and meet people's comfortable and high-paced life needs [1,2], making all consumer electronic products have the ability to connect to the network. This capability is the next development trend of consumer electronics products [3]. The networking of home appliances will bring new demands to the already saturated home appliance consumer market. Further research in this area has led to tremendous changes in people's lifestyles, working styles, and ways of thinking. It has also stimulated people's growing demand for various data sources and network services, injecting new vitality and vitality into the information society. It has important theoretical, practical and commercial value [4～6].

1 Problems existing in the field of “network information appliances”

The existing home appliance network control system still lags behind the user's requirements in terms of operation mode and ease of use. The main problems are as follows: the communication protocols of various parts of the home are different, making it difficult to form a unified home network system, and cannot be used at the application layer. Provide users with a convenient and unified interface, thereby delaying the popularization of related markets and the process of home networking. Providing a development and application-oriented interface technology that is compatible with various underlying protocols to achieve home network interoperability is a hot topic in current research among technical groups and is also the key to the further development of home networks [7].

(1) Defects and shortcomings of existing protocols and current network appliance concepts

At present, there is no unified application layer communication protocol standard. Most network home appliances require the cooperation of home appliance manufacturers, so they are technically highly dependent on speed. However, home appliance manufacturers are often unwilling to disclose their technical secrets. Incompatibility creates obstacles to the promotion of network technology.

① At present, the focus of the development of home appliance network control equipment is the home appliance control center, and this is used to promote cooperative relationships with multiple manufacturers. The idea itself is only suitable for one manufacturer. Due to its non-openness, if other manufacturers are equipped with this gateway, the control methods and strategies, and all formats of data transmission must be consistent with that manufacturer in a considerable degree. On the one hand, this limits the characteristics of each manufacturer's products and their enthusiasm for cooperation. On the other hand, it is equivalent to announcing the transmission control data format of each manufacturer, which is not conducive to competition among manufacturers. ②The particularity/diversity of user requirements for communication media brings many problems. Due to cost issues, RS485 may be selected as the communication medium in the home internal data network; in order to reduce the burden of construction and maintenance between wire connections, Power Line or other wireless transmission methods may also be selected. Embedded communication systems with multiple communication media can adapt to the needs of different consumers.

(2) Use existing network equipment to control home appliances in non-family units

In environments such as offices and other institutions, due to the popularity of Ethernet LANs, existing LANs can be directly used without occupying telephone lines. Control in the LAN is faster, more effective and more flexible, and the control strategy within the LAN can be independently orchestrated, which requires that the communication media be optional.

(3) Problems and opportunities brought about by each manufacturer’s own efforts

Network appliances should have the characteristics of network functions, digitalization, informatization, intelligence, low cost, and strong stability. However, various companies and manufacturers have different understandings of network home appliance models, and different concepts of network home appliances have emerged. If each manufacturer works independently, it will bring additional research and development expenses and provide the cost of home appliances. In addition, if there is no unified protocol, it will cause incompatibility problems in device control. On the one hand, this increases the economic expenditure of each family. On the other hand, the problem of incompatibility of multiple devices makes the network export processing confusing and will not have good applications.

(4) Copying foreign standards is not suitable for our country’s national conditions

Foreign network appliances also have similar problems. Practice shows that copying foreign standards and products is not suitable for our country's family environment. The transport layer protocols of foreign products follow standard protocols, and there are no complete and widely recognized standards for application layer protocols to follow.

In summary, it is necessary to create unified standards. A "home gateway" that maintains the characteristics of each manufacturer and protects the data transmission format of each manufacturer, and only needs to follow the necessary simple protocols to complete the control, should be supported by each manufacturer. This can change the previous traditional control strategy and establish a point-to-point communication method between users, manufacturers and specific home appliances through home gateways.

2 Principles of Application Layer Communication Protocol Development

In order to solve the current problems in the field of networked home appliances, this article provides a comprehensive solution for networked home appliances based on MCU systems. In the process of research and development of networked home appliances, the formulation of network protocols is the key. In order to bring the product to the market, the following aspects need to be paid attention to when formulating the agreement:

① Maintain the product characteristics of each electrical appliance manufacturer;

②Protect the data formats of various electrical appliance manufacturers;

③For digital home appliances, the home network controller (i.e. home gateway) only plays a channel role and assists the connection function of the home appliance manufacturer service center and the home appliance itself.

Only as follows: It is possible to seek support and cooperation from manufacturers, so there are the following principles for determining the network control protocol of the application layer:

① Each manufacturer follows a unified data format and initial data transmission protocol in terms of minimum procedures;

②Each manufacturer of home appliances can customize/parse the content of the data format;

③ Determine the data format of the same unit of home appliances, and reasonably divide the data area in EEROM for the storage of home appliance control and feedback parameters;

④ In order to ensure data communication between the user and the final control object, in principle, the manufacturer needs to provide corresponding software plug-ins, and the gateway only functions as a signal channel.

3 Home gateway design based on multiple communication media

3.1 Overall structure of home network controller

In our country, the main function of networked home appliances is to establish a convenient link relationship between family members and home appliances, to facilitate remote home appliance status preset and convenient remote control of home appliance behavior; to establish a link relationship between home appliances and manufacturer service centers to complete tasks such as remote online It has functions such as fault diagnosis, remote downloading of programs and online modification of parameters (such as online modification of product bugs and adjustment of unreasonable parameters based on regional characteristics); it has functions such as automatic fire alarm, information transmission of smart buildings and power meter reading. The overall block diagram of the home network controller is shown in Figure 1. Figure 2 is a schematic diagram of the application of network home appliances.

Users can communicate with the home gateway through three channels: A, B, and C. The home gateway has three ways of connecting with home appliances: A', B', and C'. Through round path A, users communicate with various servers in a small area on Internet nodes. After passing server identity authentication, they can communicate with the corresponding home gateway, browse the operation status of home appliances, and remotely control the behavior of preset home appliances. Using this method, users can also control directly within the LAN. Path B is to connect the PC to the Modem and communicate with the corresponding home gateway for data transmission. Path C is that the user directly uses the phone buttons to provide commands to the home gateway through DTMF decoding, and the gateway provides the user with an intuitive voice interface. For information transmission from the gateway to home appliances, Path A' applies power line carrier technology, using existing power lines as signal transmission channels, without the need for additional wiring; data from Path B' is transmitted through wireless communication, so no wiring is required; Path C' is to directly connect the gateway and home appliances with communication cables. Although this method is low-cost, it requires additional construction and wiring. In addition, in order to avoid complicated button control and LCD display, a computer is used to set parameters and edit control strategies of the home gateway through RS232.

3.2 Principle of home gateway

The principle block diagram of the home gateway is shown in Figure 3. Each component is mainly combined with the gateway application in Figure 1, and each communication interface is embedded. The IP2022 Internet processor, a new product of Ubicom Company in the United States, is selected as the main chip for home gateway control. Ubicom's IP2022 can include the communication physical layer (PHY), Internet protocol stack, special device applications and special device peripherals on one chip, and can be configured through the Internet, with a coupling current of only 100mA. IP2022 contains full-duplex serializer/deserializer (Ser/Des) hardware functions and can be directly connected to various common network interfaces. , this capability enables on-chip 10BaseT Ethernet (MAC and PHY), USB and various other fast serial protocols. Since the IP2022 chip contains 2 SerDes components to facilitate conversion from one format to another, it can also be used as a protocol converter. The operating frequency of IP2022 is 100MHz, and most instructions are executed in a single cycle, so that the throughput can meet the requirements of various new network connection applications. Therefore, the gateway can be used to control audio and video equipment, and can also be used as a web page through an Internet browser. Browsing and running home appliances, in addition to providing Bluetooth and USB interfaces for future applications.

3.3 Key technologies for home gateway design

For home appliances, cost is the key issue. The control chips of home appliances such as air conditioners, refrigerators, washing machines, etc. are mostly low-priced, dedicated CPUs. Most of these CPUs have UART communication interfaces, and even if they do not have them, they can be simulated through software; while those with other interfaces (such as USB, etc.) CPUs are generally expensive and are beyond the reach of home appliances. Unifying multiple communication protocols into UART, so that home appliances can have network functions only by changing some programs, is the starting point of this article's design. Below is a brief introduction to several key technologies involved in gateway design.

(1) Power line carrier modem

One of the biggest advantages of powerline networking is that it uses the existing power lines in the home to connect appliances to the device, eliminating the need for additional wiring. The latest technology enables very high data transfer rates and fault tolerance. The main power carrier control chips currently used include: LM1893. ST7536, SSCP200, PLT-22, etc. According to the characteristics of the home network and the performance of different power carrier Modems, we used Intellon's SSCP200 as the power carrier control chip and designed a spread spectrum carrier power line Modem with good performance, reliable operation and strong anti-interference.

(2) DTMF decoding technology

The block diagram of the telephone remote control system based on CM8870 and ISD2590 is shown in Figure 4. Currently, most phones transmit key information through dual audio signals. At the sending end, the telephone performs dual audio encoding on the key information; at the receiving end, the corresponding key information is obtained through decoding, thereby realizing the transmission of the key information on the telephone line. Simple, convenient and cheap remote control can be achieved by using phone buttons.

CM8870 is a dedicated chip for dual audio reception produced by CMD Company. It mainly includes the fourth part of the input operational amplifier, band division filter, digital decoder and output control unit. At the input end, the operational amplifier section performs necessary gain processing on the input signal. The output signal is filtered and band-divided through a band-dividing filter based on switched capacitor technology. The high-frequency group signal and the low-frequency group signal are extracted, and then the high-frequency group signal is extracted. Feature extraction is performed on the group signal and the low-frequency group signal, and the two frequencies that make up the key are finally determined. Send these two frequency values ​​to the corresponding output port for decoding, and output the corresponding key code, thus completing the detection of a key.

(3) Low-cost remote modem control technology

TI, TDK and other companies already have mature solutions, which will be omitted here.

(4) Low-cost Ethernet controlled microcontroller solution

"Broadband" has entered every home. Ethernet is not only easy to establish, but its "technical simplicity, reliability and low cost" are the advantages of Ethernet. The basic principle of the Ethernet control microcontroller solution is to parse TCP/IP, UDP and other protocols through the IP2022 protocol stack, and use a low-cost microcontroller to communicate with the protocol stack through UART, parse and execute related command operations. The principle is shown in Figure 5 .

(5) Wireless network solutions

Currently, there are many product standards for this technology, such as products from Butterfly, Diamond and other companies. The advantage of Bluetooth lies in the unification of global standards, interoperability, and the ability to easily implement fast, flexible, secure, low-cost, and low-power data and voice communications. At present, due to cost issues, Bluetooth has not really entered the home. For this, we use the lower-cost nRF401 as the wireless communication module. Its characteristics are that it does not require Manchester encoding and can directly receive/send standard serial port data. The working frequency is international The universal data transmission frequency band is 433 MHz, which meets wireless regulatory requirements and does not require a license.

Conclusion

This article applies communication principles such as power line carrier, telephone line (dual audio decoding and modulation and demodulation, etc.) and broadband network wireless network to provide a home gateway design plan based on multiple communication media, which can meet the needs of the vast majority of consumers. The application of this media multiplexing technology can ensure the centralized realization of functions such as power line meter reading, saving the total investment of households. Based on the rules of home appliance control and the protocol form that is easy for manufacturers to accept, we have developed a set of network data transmission protocols that are suitable for digital home appliances and non-digital home appliances, and are easy to communicate with and reach agreement with various home appliance manufacturers. In addition, the implementation of this protocol has nothing to do with the specific transmission media, laying the foundation for the serial development and industrialization of products. It also provides economical and reliable network solutions for applications in other fields such as home automation, distributed systems, and robot control. .