Application of RFID chip in intelligent anti-theft alarm device for automobiles

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Application of RFID chip in intelligent anti-theft alarm device for automobiles [Copy link]

Abstract: This paper introduces the radio frequency identification system with TMS3705 as the radio frequency base station, and gives its application working principle, hardware composition, software design method and software flow in the intelligent anti-theft device of automobiles. At the same time, it introduces the specific algorithm of 16-bit cyclic redundancy check used in TMS3705 information reading to improve the recognition reliability.

Radio Frequency Identification (RFID) technology is a new technology developed in recent years. It is the product of the organic combination of radio frequency technology and IC card technology. Compared with ordinary magnetic cards and IC cards, RFID technology has the advantages of easy use, fast data exchange speed, easy maintenance and long service life. In particular, it solves the two major problems of passive (no power in the card) and contactless. Unlike contact-type identification technologies such as magnetic cards and IC cards, the transponder and reader of the RFID system can complete the identification function without physical contact, so it can realize multi-target identification and moving target identification, and can be used in a wider range of occasions. The RFID system and the corresponding data verification algorithm introduced in this article are a successful attempt to apply RFID technology in car anti-theft devices.

1 Basic principles of RFID

A typical RFID system consists of a transponder, a reader, and a data exchange and management system. The basic working principle of the system is that the reader read-write terminal continuously sends out a set of electromagnetic wave signals with a fixed frequency (generally 134.2 kHz). In this way, when an LC series resonant circuit in the contactless card (transponder) chip enters the working area of the reader read-write terminal, and its working frequency is the same as the frequency of the signal sent by the read-write terminal, the LC resonant circuit resonates under the excitation of the electromagnetic wave. The resonance makes the capacitor in the card have a charge. At this time, a unidirectional conduction electronic pump connected to the other end of the capacitor can send the charge in the capacitor to another capacitor and store it. When the voltage value of the accumulated charge reaches 2V, this voltage can be used as the working power supply of the transponder. At this time, the transponder responds to the reader's request and modulates the information and sends it out for the reader to demodulate and read. The E2PROM in the transponder is used to store its unique electronic tag ID number (encoding length is 64 bits) and other user data.

Figure 1.2

Design of RFID car anti-theft alarm

The radio frequency identification system developed in this paper uses the TMS3705 of Texas Instruments as the radio frequency signal reading and writing chip, and uses the company's RI-TRP-RR2B (read-only type) as the transponder. The communication between the base station chip and the microprocessor (MCU) in this design only requires two general I/O port lines, so it is very convenient to use. The modulation and demodulation circuit is shown in Figure 1.

The signal transmitted by the transponder is received by the reader antenna and processed by the base station before being sent to the I/O port of the microprocessor. The signal sent to the reader is the FSK (Frequency Shift Keyed) signal. The reader is only responsible for the demodulation of the signal, while the decoding of the signal is completed by the microprocessor. The microprocessor can perform decoding operations based on the duration of the high and low levels of the input signal.

2.1 Data storage format in RI-TRP-RR2B radio frequency card

The RI-TRP-RR2B transponder contains 14 bytes of data, which are stored in the order listed in Table 1. The user data area contains 10 bytes, of which the 2nd to 9th bytes are the user 64-bit ID area, and the 10th and 11th bytes are the CRC check code.

Table 1 Data in RI-TRP-RR2B

1st Byte	Start byte FEH
Bytes 2 to 11	User data area
Byte 12	Stop byte FEH
Bytes 13 and 14	13th byte = 2nd byte; 14th byte = 3rd byte

2.2 Car anti-theft device based on RFID technology

The system is based on the AT89C51 microcontroller of ATMEL Company, and its hardware composition is shown in Figure 2. The system consists of a radio frequency identification device, an external memory, a voice circuit, a clock circuit, a power management circuit, a watchdog and a detection control circuit. This system has high compatibility and can be used with other anti-theft devices. It is a cost-effective car anti-theft device. The main functional features of the anti-theft alarm system are as follows:

(1) Ordinary car anti-theft devices mainly use keyboard input to identify the driver's identity, which brings many inconveniences to driving, and because of its limited password combination, it is easy to be stolen and cracked. The use of radio frequency identification technology to identify identity can effectively solve this problem. The owner only needs to carry the transponder (32mm) close to the reader's induction coil (entering the induction range of about 7cm) to complete the identity recognition in an instant, and its password is not easy to crack, thus greatly improving the anti-theft effect. If the original transponder is lost, then the user only needs to press the "learning" button and then bring the spare transponder close to the induction antenna to complete the ID learning. The original ID will be automatically cleared, and the lost transponder will be invalidated, and the spare transponder will take effect.

(2) Its external memory uses ATMEL's AT24C01 serial E2PROM. AT24C01 is a 1k-bit electrically erasable memory with an I2C bus, which can be used to store the owner's ID and the identification information of the microcontroller before a sudden power failure. Since it is a non-volatile memory, the information stored in it will not be lost after a power failure. After powering on again, the system will return to the state before the power failure, which can effectively prevent human damage to the car power supply and improve safety.

(3) The voice circuit uses the ISD1420 integrated voice chip as the core, and combined with the conditioning and power amplifier circuit, it can realize the recording and playback of multiple voice segments with good sound quality. This circuit can be used to conveniently realize the security prompt and alarm functions of the anti-theft system.

(4) The power management circuit and watchdog circuit are completed by MAX705. This chip has both power management and watchdog functions. The power management combined with the microcontroller software can be used to protect data from sudden power failure, so that the microcontroller can save the status information before the power failure to the E2PROM for reading when the power is turned on again. The watchdog circuit can effectively monitor the microcontroller to prevent various interferences on the car from causing the microcontroller to fall into an infinite loop, thereby improving the stability and reliability of the whole machine.

Figure 3 (5) The detection control circuit is used to detect various status information of the car for the microcontroller to make decisions. This includes the detection of the door, the power supply, the brake signal and the button. The control circuit includes the control of the turn signal, the power supply, the central lock and the wheel lock. 3 Software design of the radio frequency identification system

The core of the software design of the RFID system is to read and verify the signal sent by the RFID card. The identity recognition subroutine flow chart is shown in Figure 3. The RFID card used in this system is a read-only card, so it only needs to read out its unique 64-bit ID, and then compare it with the ID stored in the E2PROM after verification to determine the identity of the owner.

3.1 Reading RF Signals

Figure 4 shows the format of each byte of the signal, which consists of 10 bits. The first bit is the start bit, fixed to 1, the last bit is the stop bit, fixed to 0, and the 2nd to 9th bits are the actual transmitted data (the first received bit is LSB). Since it is negative logic, the data needs to be inverted.

Figure 5 shows the timing of the reader reading data. The data sent by the RFID card is modulated by FSK. During operation, TXCT can be set to 0, delayed for 50ms, and then TXCT is restored to 1. After about 3ms, SCIO starts to output data. The first byte of the data is the start byte, and a total of 14 bytes of data are output.

3.2 CRC data verification algorithm

CRC check is set to check whether the information field is transmitted correctly. It is a function of the information field. This paper uses a 16-bit cyclic redundancy check code (CRC-CCITT), and the generated polynomial is:

CRC checksum is widely used in communication due to its simple implementation and high accuracy. The CRC-CCITT used in this paper can detect all double errors, odd bit errors, burst errors with a burst length of no more than 16, 99.997% of burst errors with a burst length of 17, and 99.998% of burst errors with a burst length greater than or equal to 18. The operation of CRC checksum can be implemented using shift registers and half adders. The specific check principle is shown in Figure 6. The check process at the sender is as follows:

(1) First, set the initial value of the CRC check code (2 bytes) to 00H, 00H (0 to 15 in Figure 6 represent bits 0 to 15 of the CRC).

(2) All CRC check codes are shifted right by one position and an XOR operation is performed at A with the first bit of the data to be CRC checked.

(3) After the operation in step 2, if the result at A is 1, then invert the MSB (bit 15), and then check whether the MSB is 1. If the MSB is 1, then invert bit 13 and bit 10, otherwise go to step 4. If the result at A is 0, then check whether the MSB is 1. If the MSB is 1, then invert bit 3 and bit 10, otherwise go to step 4.

(4) Check whether A has been calculated 64 times. If not, repeat steps 2 to 4. (5) Repeat steps 2 to 4 to perform CRC calculations. The final value obtained is the CRC check code.

The verification process at the receiving end is actually to add the CRC check code to all the information codes, and then perform a CRC check on them as a whole. If the final result is all zeros, it means that the CRC check is correct, otherwise it means an error.

The reading of the transponder information must be carried out strictly according to its timing, otherwise the required correct information will not be obtained. Due to space limitations, this article does not list the specific procedures.

4 Conclusion

This article mainly introduces the method and implementation of applying radio frequency identification technology to automobile anti-theft system. The author has developed a new type of automobile anti-theft device using radio frequency identification technology. After several debugging and trials, its performance is not only stable, but also safe and reliable. It has also achieved good results in practical applications. Practice shows that this anti-theft device has the advantages of advanced technology, practicality, convenience, good compatibility, small size and full functions. It is an ideal automobile anti-theft system.