Abstract : This paper discusses the application of power line carrier technology based on the X-10 protocol in smart homes. The communication principle of the X-10 protocol and the nRF905 chip are explained in detail, and a control platform is designed around the nRF905 chip. The implementation process of data transmission and reception in the hardware and software designs is described, and the feasibility of the solution is demonstrated through experiments.
Keywords : Power line carrier; X-10 protocol; Smart home
Chinese Library Classification Number : TN919.3 Document Identification Code : A
Control Network Design of Smart Home Based on Electric-network Carrier Technology
Linlin Zhang 1 , Hongwei Gao 2
1) Shenyang Poly Real Estate Group Corporation Limited, Shenyang, 110001
2) School of Information Science & Engineering, Shenyang Ligong University, Shenyang, 110159
Abstract: The detail application of electronic-network carrier technology in smart home based on X-10 protocol is discussed in this paper. The theory of X-10 protocol, nRF905 chip and the control platform based on this chip is introduced. The realization process of hardware and software in data's send and receive is also introduced, the validity of this strategy is proved by experiment.
Keywords: Electronic-network carrier; X-10 protocol; Smart home
1. Introduction
Smart home technology integrates computer, network, communication, control, and wiring technologies into residences, connecting various home devices via a network. Users can conveniently control these devices using wireless remotes, telephones, or voice commands, fully embodying a people-centered lifestyle philosophy. The home network, the core of a smart home, connects all household appliances into a single network, controlling and regulating each device according to specific communication protocols. Home network control can be divided into wired and wireless control. Wireless control is primarily used outside the home, controlling electrical equipment via wireless devices such as telephones. Wired control is used within the home to control electrical equipment. Among various wired control technologies, power line carrier technology is widely used. Power line carrier technology transmits control signals to various electrical devices through power lines, forming a home network between the control unit and the appliances. Power line carrier technology is divided into high-voltage and low-voltage carriers. High-voltage carriers are used for remote control and regulation, while low-voltage carriers, due to their relatively short transmission distance, are mainly used within the home. Power line carrier technology uses power lines as the transmission medium for controlling appliances, eliminating the need for rewiring, reducing the cost of smart homes, and facilitating updates and maintenance. This paper studies the X-10 protocol and realizes the networked application of power line carrier technology in smart home control.
2. Introduction to Power Line Carrier Technology
Power line carrier communication transmits control signals over 50Hz power transmission lines, enabling centralized control of each control node via an open network structure. Currently, communication protocols used in power line carrier communication include BACnet (Building Automation and Control Network), EBI (European Installing Bus), HBS (Home Bus System), and the X-10 protocol, among others. The X-10 protocol uses a 120kHz signal frequency, significantly higher than AC signal frequencies, making it easily identifiable by the receiver. Smart home designs based on the X-10 protocol utilize power line carrier communication technology, using 220V power lines as the signal transmission medium. The X-10 protocol is also a mainstream network communication protocol in smart homes.
2.1 Introduction to the X-10 Communication Protocol
X-10 is an internationally recognized powerline carrier protocol for smart homes. X-10 enables communication between devices and transmits control commands via power lines. In 1976, the British company Pico Electronics proposed a powerline home control solution, and its engineers developed and patented the X-10 protocol. After X-10 modules were introduced to the United States, they were significantly improved technologically and began to be used in the smart home field. Since then, numerous smart home manufacturers have emerged globally, and major electrical companies such as Siemens and Samsung have also entered the smart home market.
Currently, smart home technologies can be broadly categorized into three types: X-10 power line carrier, wireless radio frequency, and centralized wiring. Compared to the latter two, X-10 power line carrier is the most mature among these three technologies due to its long development history, large user base, ease of upgrades, and low cost. While the communication technologies used by different manufacturers vary slightly, the maturity of X-10 technology has made it the mainstream technology in smart homes.
2.2X-10 Communication Principles
In network systems, in order to ensure that the two communicating parties can communicate data correctly and automatically, a set of conventions and rules have been established to address various issues in the communication process. This set of conventions and rules is called a protocol.
X-10 communicates by sending and receiving signals over power lines. Therefore, the X-10 system mainly consists of two parts: a transmitter and a receiver. Control signals are transmitted from the transmitter to the receiver via the power lines, allowing the receiver to control electrical equipment. X-10 signals are superimposed on the zero-crossing points of the AC power lines. Since interference is lower closer to zero, a 120kHz coded signal is loaded onto the 60Hz power line, with the presence or absence of a carrier signal representing "0" and "1" in the transmitted data.
Figure 1 Zero-crossing detection of the X-10 signal
The transmitter and receiver simultaneously detect the zero-crossing signal of the power line to determine when data should be transmitted, but the X-10 cannot distinguish whether the zero-crossing is a rising edge or a falling edge. Therefore, a 120kHz pulse group at the zero phase of a sine wave, followed by no pulse group at the 180° phase, indicates a signal "1". Conversely, no pulse group at the zero phase of a sine wave, followed by a pulse group at the 180° phase, indicates a signal "0", as shown in Figure 2.
Figure 2 Determination of “1” and “0”
To enable the receiver to know when to start receiving data from the transmitter, a start point needs to be set. When the receiver detects this start signal, it begins receiving data. A pulse group appears at three consecutive zero-crossing points, and no pulse group appears at the next zero-crossing point, indicating that the start point has been generated. The process is shown in Figure 3.
Figure 3. Generation of the startup code
To ensure the line relay device doesn't miss any transmitted information, the X-10 transmits each data frame twice. A complete control command consists of four data frames. The first two frames transmit the controlled device address, with no gap between them. The last two frames transmit the control command, also without a gap. However, there is a three-cycle interval between the first two frames and the last two frames, so each control command requires 47 cycles. For a 50Hz power line, 47 command cycles are close to one second.
2.3 Smart Home System Based on X-10 Protocol
X-10 is an internationally recognized powerline carrier protocol for smart homes. If the communicating parties do not share a common communication protocol, communication cannot proceed synchronously, or due to inconsistencies in data formats, they may not understand the information contained in each other's data, rendering communication practically impossible. X-10 powerline carriers provide electrical current while simultaneously transmitting control commands like a network cable, thus enabling networked control.
A smart home system built on the X-10 protocol mainly consists of a home gateway and X-10 compliant home appliances distributed throughout the home. Since most home appliances on the market do not yet support the X-10 protocol internally, an X-10 module is temporarily added between the power line and the appliance power supply. The gateway controls the X-10 module, indirectly controlling the appliances. To identify different devices in the network, a 2-digit hexadecimal code, called an address code, is used, assigning a unique address code to each controlled device in the system.
Each X-10 device is assigned an address consisting of a "room number" and a "device number". The room number is selected from the letters "AP", and the device number is selected from the numbers "1-16". Therefore, a smart home system built on the X-10 protocol can simultaneously control up to 16 × 16 = 256 X-10 devices with different addresses. This system can accommodate 256 different addresses and can execute commands including: on, off, dim, bright, alllightson, and allunitsoff. The X-10 protocol specification encodes device addresses for logical representation; when using them, simply refer to the translation table in the protocol.
3. Smart Home System Hardware Design
Smart home systems control home appliances through a unified mesh bus and control platform. The system design primarily consists of two parts: a transmitting module and a receiving module. The transmitting module uses a microcontroller program to send instructions, including the target device's address information, to the receiving module. The receiving module uses a microcontroller program to detect X-10 signals on the power line in real time. When a signal is detected, it compares the address information contained in the detected signal with its own pre-set address. If they match, it waits to receive the next X-10 control instruction; otherwise, it discards the address information and continues waiting for the next address. By responding to the corresponding instructions, it achieves real-time control of the devices.
Figure 4 System physical model
Smart home systems control home appliances through a unified mesh bus and control platform. The control mesh mainly consists of transceiver modules, wave traps, and electrical devices.
3.1 Introduction to the nRF905 Chip
The nRF905 is a monolithic RF transceiver from Nordic VLSI of Norway. It operates from 1.9 to 3.6V, is packaged in a 32-pin QFN (5×5mm) package, and supports industrial, scientific, and medical channels with a channel switching time of less than 650µs. The nRF905 consists of a frequency synthesizer, receiver demodulator, power amplifier, crystal oscillator, and modulator. It requires no external surface acoustic wave (SAW) filter, operates in ShockBurst™ mode, automatically handles headers and CRC (Cyclic Redundancy Check), and communicates with a microcontroller via an SPI interface, making configuration very convenient. Its pinout and performance are shown in Table 1.
The nRF905 has two operating modes and two power-saving modes. The two operating modes are ShockBurst™ Receive mode and ShockBurst™ Transmit mode, and the two power-saving modes are Power Off mode and Idle mode. The nRF905's operating mode is determined by three pins: TRX_CE, TX_EN, and PWR_UP.
Table 1. Pin Description of nRF905 Chip
3.2 Data Transmission Module
When data needs to be transmitted, the nRF905 must be set to operating mode. The receiver's address and the data to be transmitted are sent to the nRF905 via the SPI interface in a timely manner. At this time, the nRF905's TRX_CE and TX_EN pins are set high, activating the chip's ShockBurst™ transmit mode. Then, the RF registers are automatically enabled, the data is packaged (with a header and CRC checksum added), and the data packet is transmitted. When data transmission is complete, the data-ready pin is set high.
AUTO_RETRAN is immediately set high, and the nRF905 continues to retransmit until TRX_CE is set low. When TRX_CE is set low, the nRF905 transmission process is complete, and it automatically enters idle mode.
ShockBurst™'s operating mode ensures that once data transmission begins, even if the TRX_CE and TRX_EN pins change, the next data packet will be received only after the current data packet has been completely transmitted.
3.3 Data Receiving Module
First, by setting TRX_CE high and TX_EN low, the nRF905 is set to ShockBurst™ receive mode, causing it to continuously monitor and wait to receive data. If a carrier in the same frequency band is detected, the carrier detection pin is set high. When a matching address is received, the address matching pin is set high. At this point, the data packet reception is complete, and the nRF905 automatically removes the header, address, and CRC checksum bits, then sets the data ready pin high. Simultaneously, the microcontroller sets TRX_CE low, and the nRF905 enters idle mode. The microcontroller then transfers the data to its internal memory via the SPI interface. Once all data has been received, the nRF905 sets the data ready pin and address matching pin low. The nRF905 can then enter ShockBurst™ receive mode, ShockBurst™ transmit mode, or power-off mode.
3.4 Line Wave Blocker
Line traps typically consist of an inductive main coil, a tuner, and protective components. They are directly connected in series between the carrier signal connection point and adjacent power system components in a high-voltage transmission line to prevent signal interference transmitted through external power lines. Traps are classified according to their circuit tuning method, mainly into single-frequency/dual-frequency, band-tuned, and untuned types. Figure 4 shows the circuit diagram of a single-frequency and band-tuned trap.
Figure 4. Wave trap circuit diagram
4. Smart Home System Software Design
After entering the main program entry point, the controller is first initialized, and then zero-crossing detection is performed on X-10. Address signals and control commands are received respectively. Upon receiving the X-10 signal, the address instruction table is checked, and the address is compared with the stored address. If they match, the control command is executed; otherwise, the signal is received again.
5. Conclusion
X-10 power line carrier technology is a communication protocol developed for networked control platforms in smart homes. Due to its high cost-effectiveness and mature, stable technology, it is widely used in smart home applications. This paper constructs a networked control platform based on this protocol, making full use of power line and network resources. The feasibility of X-10 power line carrier technology in smart home applications is verified by designing a simple lighting system.
References:
[1] Yu Zhengrong. Research on the application of power line carrier technology in ship communication [D]. Master's thesis, Harbin Engineering University, 2006.
[2] Tao Guobin, Gao Bingkun, Zhang Xiuyan, Zhou Quan. Application of power line carrier technology in home control network [J]. Journal of Jiamusi University (Natural Science Edition). 2005, 23(2):180-183.
[3] Qi Mingxi, Qi Chang, Huang Tianshu. Smart home system based on power line carrier communication technology [J]. Electric Power Automation Equipment. 2005, 25(3):72-75.
[4] Zhou Hong. Intelligent Home Control System [M]. Beijing: China Electric Power Press, 2006.
About the author:
Zhang Linlin (1981–), female, engineer, currently mainly engaged in research on architectural design and intelligent buildings.
Telephone: 024-23412111
Email: [email protected]
Mailing Address: Technical Department, 7th Floor, Poly Complex Building, No. 2 Xinning Street, Shenhe District, Shenyang, 110161
