0 Introduction The development of the automotive industry has driven the development and technological upgrading of the automotive equipment industry. Among these, TPMS (Tire Pressure Monitoring System), following airbags and ABS (Anti-lock Braking System), has emerged in the international automotive field and is hailed as a new generation of high-tech automotive safety equipment. During high-speed driving, tire failure is the most worrying and difficult-to-prevent issue for all drivers, and a major cause of sudden traffic accidents. Statistics show that 70% to 80% of traffic accidents on highways are caused by tire blowouts. How to prevent tire blowouts has become an important issue for safe driving. According to relevant experts, maintaining standard tire pressure and timely detection of tire leaks are key to preventing blowouts. Research on tire pressure monitoring devices began abroad in the late 1970s. These devices can be broadly categorized into two types: one based on wheel speed (indirect); and the other based on pressure sensors (direct). Currently, the United States and some European countries have made TPMS a mandatory feature in automobiles. Although research on TPMS in China started relatively late, the national standard "Technical Conditions for Safe Operation of Motor Vehicles (Draft for Comments)," promulgated on November 24, 2003, included instructions for installing tire pressure monitoring devices, indicating that China has begun to attach importance to the development of TPMS. The TPMS proposed in this paper adopts a modular design and standardized programming. Its core component is the wireless transmission and reception of collected temperature and pressure data. The CC1100 wireless transceiver chip produced by Chipcon can effectively solve this problem. It supports ZigBee wireless network technology, has low power consumption, requires no frequency application, and provides reliable transmission. 1. Tire Working Characteristics and TPMS Technical Requirements Tires are made of rubber and reinforcing materials, mounted on the outer side of the tire sheath, supporting the weight of the vehicle, absorbing and mitigating shocks and vibrations, and maintaining good adhesion between the vehicle and the ground, thereby effectively transmitting the vehicle's driving torque or braking torque. The working characteristics of tires have a significant impact on the safe driving of vehicles. The main factors affecting the normal working characteristics of tires are: a) Excessively high tire temperature. High ambient temperatures and friction between the tire and the ground during high-speed rotation can cause tire temperatures to rise excessively, leading to rubber aging and shortening tire lifespan. b) Excessive or insufficient tire pressure. When the vehicle load is too high or the temperature is too high, causing the gas inside the tire to expand, excessive tire pressure can lead to a tire blowout. c) Tire leakage causing insufficient pressure also increases friction between the tire and the ground, increasing fuel consumption and shortening tire lifespan. The mechanical performance of a tire is mainly reflected by its internal temperature and pressure. Therefore, as long as the TPMS can detect the internal temperature and pressure of the tire in real time, it can analyze the tire's operating status. Since the TPMS transmitting system is located within the closed system of the tire, the main technical requirements are as follows: a) Considering installation and the use of button batteries for power, the sampling transmitter should be small in size and have low power consumption. b) The system should be able to identify the temperature and pressure measurements sent from each sampling transmitter. c) The system should be able to filter out any data sent from other vehicles. d) The receiving end should be able to display the temperature and pressure measurements sent from each sampling transmitter in real time and provide over-limit alarms. 2. TPMS Principle and Hardware Design 2.1 TPMS System Structure The TPMS consists of a sampling and transmitting module and a receiving module. The sampling and transmitting module is installed inside the tire, and the receiving module is installed inside the vehicle compartment. The sampling and transmitting module samples the air pressure and temperature signals detected by the pressure sensor. After data analysis and processing by the MCU (Microcontroller Unit), the data is sent to the radio frequency transmitting circuit. The signal is modulated and then transmitted to the receiving module. The demodulation circuit of the receiving module amplifies and demodulates the radio frequency signal transmitted by the transmitting module, and then sends the digital signal to the MCU. The MCU performs corresponding processing, such as updating the current pressure value and issuing audible and visual alarms, thereby realizing the display and monitoring of tire pressure. The block diagram of the TPMS structure, consisting of the sensor, MCU, transmitting, and receiving chips, is shown in Figure 1. The overall system layout is shown in Figure 2. 2.2 System Function and Overall Design The TPMS sampling and transmitting module operates under conditions of severe vibration, large temperature variations, and inconvenient maintenance. Therefore, all components are required to have high reliability and stability, and be able to adapt to a wide temperature range and severe vibration. To reduce the size of the TPMS sampling transmitter module, save power, and enhance functionality, a low-power, high-performance chip is required. Extending the battery life of the TPMS sampling transmitter module to 3-5 years is crucial for system power saving. Power saving and extended battery life are achieved only when the system is in sleep mode most of the time. The main functions of the system are as follows: a) Real-time monitoring of the temperature and pressure of each tire. b) Alarm when the pressure of a tire is too high or too low. c) The position number of each tire sampling transmitter module can be reset during tire maintenance and repositioning. d) Display of the current pressure and temperature values ​​of each tire. During installation, the five modules are activated and registered one by one. The receiver receives the unregistered ID (identification code) from the sampling transmitter module and registers it, with the corresponding tire number set manually. The receiver's MCU stores the ID and tire code in E2PROM for normal operation. If a module in a tire fails, the ID of the sampling transmitter module to be changed can be deleted from the host receiver module and re-registered. The tire code can be reset in the host receiver module after tire maintenance and repositioning. Due to the non-repetitive nature of the IDs of each sampling transmission module, mutual interference between the five tire sampling transmission modules of the same vehicle or between sampling transmission modules of different vehicles can be effectively avoided. When the car is moving, the vibration sensor in the receiving module detects the car's vibration signal, and the TPMS is activated. The host sends a command through the transceiver chip to wake up the sampling transmission module from sleep mode. The sampling transmission module sends out the temperature and pressure values ​​inside the tire after packaging them. The receiving module compares the ID in the received data packet with the ID and tire code stored in the host E2PROM to determine which tire's data it is, and stores and displays it. When the tire pressure is too high or too low, an alarm is triggered. When the car is stopped, the vibration sensor does not detect the vibration signal, and the TPMS enters sleep mode. When the car is stopped, if the driver wants to know the temperature and pressure values ​​inside the tire, they can activate the TPMS by pressing a button to read the current tire pressure and temperature values. 2.3 Wireless Sampling Transmission Module Design The sampling transmission module consists of SP12, ATmega48 (hereinafter referred to as AT48) and CC1100. SP12 is a pressure sensor. The SP12 has a measurement range of 100 kPa to 4500 kPa and internal A/D and SPI (Serial Peripheral Interface) capabilities, making it easy to use in TPMS. It comes in a 14-pin surface-mount package and requires no external components. The AT48 is an ultra-low-power 8-bit CMOS MCU manufactured by Atmel, based on an AVR-enhanced RISC (Reduced Instruction Set Computer) architecture. Normal mode is: 1 MHz, 1.8 V/300μA; 32 kHz, 1.8 V/20μA (including oscillator); power-down mode is: 1.8 V/0.5μA. The CC1100 is a low-cost, monolithic programmable UHF transceiver chip based on Chipcon's Smart RF technology, designed for low-power wireless applications. It operates flexibly in the ISM (Industrial, Scientific, and Medical) and SRD bands of 315 MHz, 433 MHz, 868 MHz, and 915 MHz. It features low power consumption (receive current less than 16 mA, transmit current less than 30 mA, sleep current less than 10 μA) and supports ZigBee wireless network technology. The main operating parameters of the CC1100 can be programmed via the SPI interface, making it more flexible to use. The sampling and transmitting module circuit design is shown in Figure 3. The sensor SP12 sends the collected data to the AT48, which then sends the data to the CC1100 via the SPI port. The CC1100 then converts the data into data frames and sends them to the host receiving module. The module's transmission frequency is determined by the crystal oscillator of the CC1100 and external components. This system selects a transmission frequency of 433 MHz, where pins 8 and 10 are connected to pin 26. A MHz crystal oscillator. C2 is (3.9±0.25) pF, C3 is (3.9±0.25) pF, C4 is (8.2±0.5) pF, C5 is (5.6±0.5) pF, C6 is 220 pF±5%, C7 is 220 pF±5%, L2 is 27 nH±5%, L3 is 27 nH±5%, L4 is 22 nH±5%, and L5 is 27 nH±5%. Resistor R2 is used to set a precise bias current. C3, C2, L2, and L3 form a balanced converter to convert the differential RF port on the CC1100 into a single-ended RF signal. The CC1100 supports amplitude, frequency, and phase-shift modulation formats, which can be configured via the register MDM-CF2.MOD_FORMAT. The CC1100 is configured to WOR (electromagnetic wave activated) mode by setting the WORCTRL register, and the register bit MCS1.RX-OFF_MODE is set. When the sampling and transmitting module receives a valid data packet, the CC1100 is activated and enters the transmitting mode, simultaneously waking up the AT48. 2.4 Wireless Receiver Module Design The receiving circuit consists of the wireless transceiver chips CC1100 and AT48, as shown in Figure 4. CC1100 and AT48 transmit data through the SPI port. In the receiving state, SCLK is used as the synchronization clock. When CC1100 receives valid data information, it sends the digital signal to the SPI port of AT48. AT48 decodes the received data, extracts the temperature and pressure values ​​of each tire from the data stream, and then performs corresponding processing, such as updating the current temperature and pressure values, and issuing audible and visual alarms. Before receiving, AT48 initializes and configures the corresponding registers of CC1100 by writing relevant data to the SPI data register SPDR, and then waits to receive data. 3. Software Design 3.1 System Topology The receiving module and sampling module adopt a master-slave configuration. The receiving module can be considered the master device, and the sampling module inside the tire is the slave device. To achieve reliable wireless communication between the sampling transmitting module and the receiving module, they must communicate using a specific protocol. The ZigBee network includes a coordinator, FFD (Full Function Device), and RFD (Reduced Function Device), and supports three network topologies: star, tree, and mesh. Considering that a typical car has four tires and one spare tire, the sampling transmitting module in each tire acts as a child node in the ZigBee network. Child nodes do not transmit data among themselves, only communicating with the receiving module inside the vehicle; therefore, a star topology is chosen. The RFD child node transmits data in frames to the receiving end via the ZigBee wireless network. The receiving host then analyzes, processes, and displays the data. Figure 5 shows the data frame format of the ZigBee network. 3.2 Software Design The communication mode between the sampling transmitting module and the receiving module (host) is shown in Figure 6. The data frame format sent by the sampling transmitting module to the receiving module is shown in Figure 7. 3.2.1 Sampling and Transmission Module Program Flow The main program flow of the sampling and transmission module is shown in Figure 8. When the CC1100 detects a wake-up command, it is activated and wakes up the MCU. The MCU configures the CC1100 to enter transmission mode. After the MCU collects and processes the data detected by the sensor inside the tire, the CC1100 sends it to the host. After successful transmission, the CC1100 and MCU return to sleep mode. The register configuration is shown in Table 1. 3.2.2 Receiving Module Program Flow The program flow of the receiving module is shown in Figure 9. After power is turned on, the AT48 first initializes and then configures the CC1100. When the MCU detects a vibration signal, it sends an activation command to the sampling and transmission module. After successful transmission, it immediately enters receiving mode. If the CC1100 is ready to receive, it can receive data. If the received data is valid, the received ID is compared with the ID code stored in the microcontroller's E2PROM. If they match, the data is processed and saved. When the detected temperature or pressure values ​​deviate from normal values, an alarm is triggered to alert the driver. The driver can also view the currently detected temperature and pressure values ​​inside the tire on the display. The specific implementation program segment is as follows: 4. Conclusion This paper proposes a TPMS based on ZigBee wireless network technology and the CC1100 wireless transceiver chip. It fully utilizes the characteristics of the CC1100, AT48, and SP12 sensors, employing low-power, low-complexity ZigBee network technology as the communication protocol. In electromagnetic wave activation mode, the CC1100 can enter a deep sleep state after successfully sending a data packet, significantly reducing module power consumption. Each tire is assigned a fixed ID code to avoid external interference. The driver can manually read the temperature and pressure values ​​of any tire from the cab, monitoring tire conditions in real time and preventing tire failures. The implementation of this system provides an effective way to prevent tire blowouts.