Application of Zigbee wireless network in automobile tire pressure monitoring
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1 Zigbee technology overview
Zigbee technology is a short-distance, low-complexity, low-power, low-data-rate, and low-cost two-way wireless communication technology. It is mainly suitable for automatic control and remote control. It can be embedded in various devices and supports geographic positioning functions. . Generally speaking, as the communication distance increases, the complexity, power consumption, and system cost of the device are increasing. Compared with various existing wireless communication technologies, Zigbee technology will be the technology with the lowest power consumption and cost. At the same time, based on the characteristics of low data rate and small communication range of Zigbee technology, it also determines that Zigbee technology is suitable for carrying services with small data traffic. The main advantages of Zigbee technology are: power saving, reliability, low cost, short delay, large network capacity, and security.
Zigbee is a set of technical standards related to networking, security and application software developed based on the 802.15.4 wireless standard approved by IEEE. It is not just the name of 802.15.4. IEEE only deals with low-level MAC layer and physical layer protocols, and the Zigbee Alliance standardizes its network layer protocols and APIs. The full protocol is used for 4K bytes that can be directly connected to the basic node of a device at a time or 32K bytes as a hub or router coordinator. Each coordinator can connect up to 255 nodes, and several coordinators can form a network, and there is no limit to the number of routing transmissions. The Zigb ee Alliance has also developed a security layer to ensure that this portable device will not accidentally leak its identification, and that this long-distance transmission using the network will not be obtained by other nodes.
The complete Zigbee protocol suite consists of high-level application specifications, application convergence layer, network layer, data link layer and physical layer. The protocol above the network layer is formulated by the Zi gbee Alliance, and IEEE802.15.4 is responsible for the physical layer and link layer standards. Figure 1 shows the Zigbee protocol architecture.
2 Application of Zigbee in automobile tire pressure monitoring system
At present, the number of vehicle traffic accidents on expressways is increasing, and most of them are caused by tire blowouts caused by tire pressure that is too high or too low. The tire pressure monitoring system monitors the pressure in the tires around the clock, monitors and alarms tire leakage, low pressure, and high pressure, so that the vehicle is always in a safe operating state. Try to avoid traffic accidents caused by tire pressure.
Zigbee is mainly used between various electronic devices with short distances, low power consumption and low transmission rates. Typical transmission data types include periodic data, intermittent data and low response time data. According to assumptions, its application targets are mainly: industrial control (such as automatic control equipment, wireless sensor networks), wireless car monitoring (such as tire pressure, temperature, etc.), medical care (such as monitoring and sensing), home intelligent control (such as lighting) , Water and electricity metering and alarm), remote control devices of consumer electronic equipment, wireless connection of PC peripherals and other fields.
2.1 System composition and principle
The tire pressure monitoring system consists of a tire pressure sensor, a controller, a radio frequency transmitter and a receiver. Tire pressure sensor The integrated capacitive pressure sensor MPXY8020A developed by Motorola as the tire pressure detection unit has the characteristics of low power consumption and full integration. Adopt Zigbee module CC2430 as signal control processing and transmitting and receiving unit.
The pressure sensor installed in each car tire transmits the pressure and temperature information in the tire through the radio frequency transmitter to transmit the tire pressure and temperature information from the inside of the tire to the receiver module in the cab, allowing the driver to run the car. Understand the working conditions of the tire, check whether the tire pressure and temperature are normal, and give an abnormal alarm to ensure safety. The smart tires cooperate with a receiver and display on the car dashboard to form a tire pressure monitoring system (TPMS).
2.2 Application of CC2430 in automobile inspection system
The principle structure of the tire pressure detection system with CC2430 as the core of the transmitter, receiver and data processing element is shown in Figure 2.
1) Processing of sensor data. The pressure sensor (Motorola part number MP XY8020A) installed in each car tire (4 wheels on the car, 1 spare wheel) is a capacitive ME MS pressure sensor, dedicated to meet the compatibility of TP MS in temperature and pressure media Requirements. It is a single pressure and temperature sensor with power management and digital output functions.
2) Transmission of tire data. In order to ensure the reliability of sending and receiving data in harsh environments, and according to the small amount of information and simple data of this application, the method of information redundancy is used to ensure reliable data reception, that is, the same content of information is continuously sent. For data sending and processing, the CC2430 module is used here.
3) Tire data reception. In order to reduce power and save battery power, an acceleration sensor is installed in the cab data processor. Once the vehicle is started, the pressure detection and transmission circuit in each tire is activated, the vehicle stops, and the tire circuit enters sleep mode.
4) Tire pressure display and alarm. According to the tire type and season, the tire pressure and temperature data can be set in the cab controller. The controller continuously receives tire data when the vehicle is running, and performs data analysis, storage, and display. If there is an abnormality, the alarm will alert the driver. The data stored in FLASH can be used to analyze the accident afterwards.
2.3 CC2430 module
The CC2430 chip is supported by a powerful integrated development environment, and the interactive debugging of internal circuits is supported by the IAR industry standard that complies with the IDE, which is highly recognized by embedded institutions. It combines Chipcon’s global advanced Zigbee protocol stack, toolkit and reference design to demonstrate the leading Zigbee solution. Its products are widely used in fields such as automobiles, industrial control systems and wireless induction networks, as well as other devices with 2.4 G Hz frequencies besides Zigbee.
1) The main features of the CC2430 chip: high-performance and low-power 8051 microcontroller core: integrated 2.4GHz RF radio transceiver that meets the IEEE802.15. 4 standard; excellent wireless receiving sensitivity and strong anti-interference ; In sleep mode, only 0.9 current consumption, external interrupt or RTC can wake up the system; in standby mode, less than 0.6 current consumption, external interrupt can wake up the system; hardware supports cSMCA function; wider Voltage range (2.0～3.6V); digital RSSI/LQ1 support and powerful DMA function; battery monitoring and temperature sensing functions; integrated 14-bit ADC with analog-to-digital conversion; integrated AES security coprocessor; Comes with 2 powerful USARTs that support several groups of protocols, and 1 MAC timer compliant with IEEE802.15. 4 specifications, 1 conventional 16-bit timer and 2 8-bit timers; powerful and flexible development tools . The basic composition block diagram of Zigbee of CC2430 is shown as in Fig. 3.
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