Design of smart home system based on ZigBee

Smart home is based on the house as a platform, using integrated wiring technology, network communication technology, security technology, automatic control technology, audio and video technology to integrate facilities related to home life, build an efficient management system for residential facilities and family schedule affairs, improve home safety, convenience, comfort, artistry, and achieve an environmentally friendly and energy-saving living environment. Based on the latest definition of smart home and referring to the characteristics of ZigBee technology, this system is designed. On the basis of including the necessary systems of smart home (smart home (central) control management system, home lighting control system, home security system), it also adds home wiring system, home network system, background music system and home environment control system. In the recognition of smart home, only the home system that has fully installed all the necessary systems and at least one or more optional systems can be called smart home. Therefore, this system can be called a smart home.

1 System Design Scheme
The system design consists of controlled devices and remote control devices in the home. The controlled devices in the home mainly include computers that can access the Internet, control centers, monitoring nodes, and optional home appliance controllers. The remote control devices mainly consist of remote computers and mobile phones. The system composition is shown in Figure 1.

The main functions of the system are: 1) browsing the front-end web pages and managing the background information; 2) realizing the switch control of indoor household appliances, security and lighting through two remote control methods, the Internet and mobile phone; 3) realizing user identification through the RFID module, so as to complete the switch of the indoor security status, and send an alarm to the user through a short message (SMS) when the thief breaks in; 4) completing the local control and status display of indoor lights and home appliances through the central control management system software; 5) using the database to complete the storage of personal information and indoor equipment status, and conveniently allowing users to query the indoor equipment status through the central control management system.

2 System Hardware Design
The system hardware design includes the design of the control center, monitoring nodes and the selected household appliance controller (here the electric fan controller is taken as an example).
2.1 Control Center
The main functions of the control center are: 1) Establishing a wireless ZigBee network, adding all monitoring nodes to the network, and receiving new devices; 2) User identity recognition, the user uses the user card to switch the indoor security when leaving or returning home; 3) When a thief invades the room, the alarm is sent to the user by sending a short message. The user can also control the indoor security, lighting and home appliances through short messages; 4) When the system is running alone, the LCD displays the current system status for the user to view; 5) Store the status of electrical equipment and send it to the PC to realize the system online. According to the functions of the control center, its composition block diagram is designed as shown in Figure 2.

The CC2430 microcontroller from TI is selected as the controller of the ZigBee module. It is a high-performance, low-power 8051 core microcontroller. It is also a 2.4 GHz radio frequency device that complies with the IEEE802.15.4 specification. The hardware supports carrier sense multiple access/collision detection (CSMA/CA). The operating voltage of 2.0-3.6 V is conducive to achieving low power consumption of the system. Through the ZigBee coordinator module connected to the control center, a wireless star-shaped ZigBee network is established indoors. All monitoring nodes and selected household appliance controllers are
added as terminal nodes in the network to achieve wireless ZigBee network control of indoor security and household appliances.
The control center MCU uses an 8-bit microcontroller ATMegal28. This device is a high-performance, low-power RISC structure microcontroller. Most instructions can be completed within 1 clock cycle. It works at a maximum of 16 MHz. It has 128 K of in-system programmable Flash, 4 K bytes of EEPROM and 2 serial interfaces. It is connected with GSM module, RFID module, LCD module, ZigBee coordinator and PC, and is the core of the whole hardware system, completing the response to the central control management system and driving each module. The GSM module adopts TC35i module. It is directly connected to the control center MCU through the serial UART interface. The RFID module adopts ZLG500 module, which integrates MFRC500 ISO14443A card reader, which can read and write the EEPROM in RC500. Since ZLG500 does not adopt the standard SPI interface specification, it can only be connected to the general I/O interface of the microcontroller to achieve communication. The LCD module uses 1602 LCD and adopts a 4-wire interface to connect to the general I/O interface of the control center MCU. The ZigBee coordinator and the control center MCU adopt a 2-wire interface to realize bidirectional data transmission between the two. The control center MCU is connected to the computer RS232 serial port, and the data transmission is stable, reliable and real-time.
2.2 Monitoring nodes
The functions of monitoring nodes are: 1) detection of human signals, sound and light alarm when thieves invade; 2) control of lights, which are divided into automatic control and manual control. Automatic control is to automatically turn on/off the lights according to the intensity of indoor light, and manual control is to achieve lighting control through the central control management system; 3) send alarm information and other information to the control center, and receive control instructions from the control center to complete equipment control. Based on the functions of monitoring nodes, the composition of monitoring nodes is shown in Figure 3.

The infrared plus microwave detection mode is currently the most commonly used method for human signal detection. The pyroelectric infrared probe here uses RE200B, and the amplifier uses BISS0001. RE200B is powered by 3-10 V voltage, and has a built-in pyroelectric dual-sensitive infrared element. When the element receives infrared light, a photoelectric effect occurs at the two poles of each element and accumulates charge. BISS0001 is a digital-analog hybrid special integrated circuit composed of an operational amplifier, a voltage comparator, a state controller, a delay timer, and a blocking time timer. It can form a passive pyroelectric infrared switch with RE200B and a small number of components. The microwave sensor uses the ANT-G100 module, with a center frequency of 10 GHz and a maximum settling time of 6μs. Combined with the pyroelectric infrared module, it can effectively reduce the target detection error rate.
The light control module is mainly composed of a photoresistor and a light control relay. The photoresistor is connected in series with a 10 kΩ adjustable resistor, and the other end of the photoresistor is grounded, and the other end of the adjustable resistor is connected to a high level. The voltage value of the two resistor connection points is obtained through the analog-to-digital converter of the single-chip computer to determine whether the current light is on. The adjustable resistor can be adjusted by the user to meet the light intensity set by the user when the light is just turned on. The switch of the indoor light is controlled by a relay. Only one input and output port is required.
2.3 Select the household appliance controller to be added
The control of the household appliances selected to be added is mainly based on the function of the device to realize the device control. Here, the electric fan is taken as an example. The control of the electric fan is that the control center sends the electric fan control command issued by the host computer to the electric fan controller through the ZigBee network. Different household appliances have different identification codes. For example, this protocol stipulates that the identification code of the electric fan is 122, and the identification code of the household color TV is 123, so that the control center can identify different household appliances. For the same instruction code, different household appliances perform different functions. Figure 4 shows the composition of the household appliances selected to be added.