Aiming at the problems of independence, hardware redundancy and high production cost of existing vehicle access control system and tire pressure monitoring system, a design scheme of vehicle security system based on RFID technology is proposed. In terms of radio frequency communication, the system adopts the combination of 434 MHz UHF band and 125 kHz lf band to realize the functions of tire pressure monitoring, remote control door lock and engine anti-theft locking.

Automobile security system based on RFID Technology

Radio frequency identification (RFID) is a non-contact automatic identification technology. The car security system uses radio frequency identification technology, through the radio frequency signal to automatically identify the target object and obtain relevant data. RFID technology uses radio frequency transmission, which can read chip data through external materials to achieve non-contact operation. The communication data is encrypted by encryption algorithm to realize data security storage, management and communication. With the rapid development of electronic technology and the improvement of electronic chip integration, the cost of RFID system is constantly reducing, which speeds up the promotion and application of intelligence in the automotive electronics industry.

The intelligent vehicle security system is composed of tire transmitting module, remote key module and base station module. For RFID system, the size of transceiver frequency determines the identification distance of RFID system, the difficulty of circuit implementation and the cost of hardware design. In the design of automobile security, low frequency (LF) bands such as 125 kHz are used for the identification of automobile engine anti-theft system with short distance, low speed and less data requirements; ultra high frequency (UHF) bands such as 434 MHz are used for the identification of long-distance radio frequency communication system (automobile tire pressure monitoring system and remote keyless entry system).

1. System composition

The overall structure of the system is shown in Figure 1. The system consists of tire module, key module and base station module.


Taking a car with four tires as an example, the system consists of four tire modules, one key module and one base station module. The base station module includes RF receiver, lf transceiver, central control part, man-machine interface and LIN bus used to transmit ignition and door control commands. The four tire modules are installed in the four tires of the car respectively. The pressure, temperature and battery voltage parameters of each tire are measured in real time, and the measured data is sent to the base station module for processing through RF communication. The base station module, on the one hand, receives the RF data from the tire module, and further judges whether the tire parameters are normal or not. If it is abnormal, it will give a real-time alarm; On the other hand, it receives the RF control data from the key module and verifies whether the ID of the key is legal. If it is abnormal, it gives an alarm in time. If it is normal, the base station sends a confirmation message to the door control actuator to realize the start / lock action; At the same time, the base station module communicates with the key module through LF communication, and uses the password of the transponder in the key module to match with the password in the base station module to control the start of the engine, so as to achieve the purpose of anti-theft. The base station can be connected with other electronic systems in the car through the car bus to share data and control information in real time.

2. System hardware design and Implementation

Tire module circuit

The tire module is composed of data acquisition and transmission circuit of tire status, as shown in Figure 2.


The tire module circuit adopts Freescale’s intelligent embedded sensor mpxy8300. This series of sensors integrates the company’s low-power S08 core, including 512 byte ram and 16 KB flash. At the same time, it also integrates low-power capacitive pressure and temperature sensors and single channel low-frequency input interface. Its RF transmission supports 315 MHz and 434 MHz carrier frequencies, and its registers can be programmed to ask or FSK modulation. It also integrates charge pump function. When the battery voltage is low, it can increase the power supply voltage of RF emission part, so that it can still achieve a certain RF emission intensity.

Mpxy8300 is a system on chip (SOC) that integrates pressure and temperature sensor, 8-bit microcontroller (MCU), RF transmitter and dual axis (XY) accelerator into one chip. Mpxy8300 pressure measurement range: Car 100 ~ 800 kPa, truck 100 ~ 1 400 kPa, temperature measurement range: – 40 ~ 125 ℃.

Key module circuit

The key module chip is pcf7961 produced by NXP company.

Pcf7961 is a reduced instruction set (RISC) processor based on low-power 8-bit mrkii architecture, which integrates UHF Transmitter and LF transceiver chips. This kind of chip can complete RF transmitter and transponder low frequency communication authentication, which is suitable for remote control and anti-theft devices of motor vehicles. It adopts fast mutual authentication algorithm, uses random numbers, key and password, and has the characteristics of high sensitivity (long distance) and short authentication time (39 MS).

Pcf7961 also provides a 32-bit identification code (ID) that has been solidified at the factory. Figure 3 is the schematic circuit diagram of the key module.


  Base station module circuit

The base station module is mainly composed of RF receiving circuit, low frequency transceiver circuit, MCU, Lin interface and man-machine interface. The RF receiving circuit uses Freescale’s UHF RF receiver chip mc33596. After signal demodulation and data Manchester decoding, the data is transmitted to the master control chip MC9S08DZ60 of the base station for data processing (RKE data decryption) and instruction execution.

Pjf7992 produced by NXP company is used as low frequency transceiver. Pjf7992 integrates all necessary functions to facilitate reading and writing balise. Base station microprocessor controls the communication between pjf7992 and balise through Lin serial interface of pjf7992.

MC9S08DZ60 produced by free SC ale company is used as the master control chip of base station. It can configure and communicate the parameters of mc33596 through SPI serial bus. Two SCI (Lin) modules are integrated in MC9S08DZ60, which can control the low-frequency transceiver chip pjf7992 through one LIN bus, and transmit commands to the engine electronic control unit (ECU) and the door control related actuator through the other LIN bus. By adding LIN bus interface to the car security system, the system can share data and control information with other electronic control systems in the car, which greatly improves the security and flexibility of the system.

Editor’s comments:This paper introduces an automobile security system circuit based on RFID technology, which realizes the functions of tire pressure monitoring, remote control door lock and engine anti-theft locking. LIN bus interface is added in the system, which enables the system to share data and control information with other electronic control systems in the automobile.

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