Design of network-based car anti-theft system using ARM7

introduction

With the improvement of people's living standards, cars have gradually entered families, but the increasingly rampant car theft cases are also on the rise. How to effectively prevent car theft is the most concerned issue for car owners. In recent years, science and technology have developed rapidly, and new car anti-theft equipment combining various new technologies has appeared one after another. With the development of communication technology, wireless remote communication technology has also been applied to the automotive field. The network-based car anti-theft control system based on S3C44B0X is an embedded system constructed with ARM 7 microprocessor, combining traditional anti-theft technology and new GPRS wireless communication technology, realizing the existing functions of the existing anti-theft device, and developing remote control functions, which improves the security, flexibility and reliability of the anti-theft system.

1. System Design

1.1 System features and functions

After analyzing the characteristics of various types of car anti-theft systems, a network-based car anti-theft control system based on S3C44B0X was designed. It fully utilizes the advantages of GPRS wireless communication technology based on the GSM network: ubiquitous, fast access, always online, flow metering, etc. At the same time, it also utilizes the advantages of the ARM7 microprocessor: 32-bit core, high performance, low cost, low power consumption RISC microprocessor, and many cooperative development partners. As the functions of the anti-theft system become more and more complex, in order to facilitate the effective development of system programs and the expansion of system functions, an embedded system is used for development, which improves the flexibility, security and reliability of the system. The main functions implemented by the system are as follows:

(1) Based on the GSM global networking function, the GPRS communication network is used to realize the anti-theft alarm function across the country.

(2) Intelligent remote control or mobile phone to achieve locking and unlocking functions, conveniently and quickly enter and release the anti-theft state.

(3) Once an alarm occurs, a message can be sent to your mobile phone in a very short time, realizing silent and automatic alarm, achieving the unique effect of "I know but the thief doesn't know".

(4) When a vehicle is robbed or stolen, use a mobile phone to send a control text message to the car anti-theft device to cut off the power or fuel and force the car to stop.

(5) After the anti-theft function is set, if the car door, trunk, or hood is forcibly opened without the owner's permission, or the car is vibrated, an alarm will be sounded and a text message will be sent to the owner's mobile phone.

(6) Microcomputer power-off and fuel-off function: the vehicle enters anti-theft state and automatically cuts off power and fuel through microcomputer control, making it impossible to start the vehicle.

(7) After entering the anti-theft mode, even if the thief cuts off the power supply, the alarm can be sounded as usual, and the alarm will be sounded once every 1 minute, that is, a message will be sent to the mobile phone.

1.2 System hardware design

The system hardware mainly consists of two parts: one is an embedded system platform built with S3C44B0X microprocessor, with GPRS module, which is used as the main control board of car anti-theft; the other part is the car circuit signal interface board, which is mainly used to obtain the status signal of the car and send control signals to the car. Figure 1 is the hardware block diagram of the system.

The CPU uses SAMSUNG's ARM7 series chip S3C44B0X. S3C44B0X has excellent core performance, rich external interfaces and low power consumption. The system clock is 66MHz, supports LCD, has 8 memory banks, the maximum memory can be expanded to 256M, and can easily connect various types of memory; it can run operating systems without MMU management, and can efficiently and conveniently implement relatively complex control; we use 2 types of memory in the system, one is SDRAM and the other is FLASH;

Figure 1 System hardware block diagram

SDRAM dynamic memory runs fast, but cannot save data after power failure. It is mainly used to run operating systems, applications and caches of various data in the system. There are many types of SDRAM, and there are products from various manufacturers. The performance difference is not too big. The main consideration is the memory capacity. We choose a more common chip, HY57V641620HC from Hynix, which is a 1M×l6bit×4bank synchronous DRAM.

FLASH memory runs slower than SDRAM, but can save data after power failure. FLASH has two types: NAND and NOR. The characteristic of NOR is in-chip execution, so that the application can run directly in the flash memory without having to read the code into the system RAM. NOR has high transmission efficiency and is very cost-effective at a small capacity of 1 to 4MB, but its slow writing and erasing speeds greatly affect its performance. NAND structure can provide extremely high cell density, can achieve high storage density, and has fast writing and erasing speeds. The difficulty of using NAND lies in the management of flash and the need for special system interfaces. A general-purpose FALSH (SST39LV160) with a capacity of 2MB is also selected in the system. It is mainly used to solidify the startup code and control the application, and save some system data and the owner's mobile phone number.

The communication with the mobile phone uses the SIM100 GSM/GPRS module provided by SIMCOM Co., Ltd. This module has a standard AT command interface and can provide GSM voice, SMS and GPRS Internet access services. In the system, SMS is used to achieve remote wireless anti-theft control.

An LCD and keyboard are also added to the system. The LCD uses 1602 and can display 2 lines of characters, 16 letters per line. It is mainly used to display some prompts and status information. The keyboard is used to set the owner's mobile phone number.

The main control board has added an interface with the car control detection board. Through the detection interface, the main control board can obtain the current state of the car, such as the open and closed state of the door, the state of the foot brake and hand brake, whether the car is started, etc. According to these states, the controller can implement corresponding control of the car. The main control board implements corresponding control of the car through the control interface, mainly the control of the car's double jump lights, alarm horn and ignition.

1.3 System software design

The software system of car anti-theft can be divided into two parts: one part is the processing of the armed state; the other part is the processing of the unarmed state.

In the fortified state, when the car is stolen or damaged, the alarm will sound and light alarm, and send an alarm text message to the owner's mobile phone. The owner can judge the authenticity of the information: if it is a real alarm, the alarm can be called and the car can be turned off at the same time; if it is a false alarm, the alarm can be canceled through the mobile phone and the car can be put into anti-theft monitoring state again. The fortified state is divided into audible anti-theft and silent anti-theft. In audible anti-theft, if the car is stolen, the sound and light alarm will be sounded at the same time; in silent anti-theft, if the car is stolen, only the light alarm will be sounded, and there will be no sound alarm. In both cases, a stolen text message will be sent to the owner's mobile phone.

In the unguarded state, there will be no alarm. Only in the case of some illegal operations, the owner will be warned of danger through sound and light, such as when the car is started and the door is not closed properly. The overall process of the system software is shown in Figure 2.

Figure 2 The overall process of the system software[page]

3. Key technologies of the system

There are two key technologies used in the system, one is GPRS remote wireless data transmission, the other is the reading and writing of FLASH memory.

3.1 GPRS data transmission process

GPRS remote wireless data transmission mainly completes the sending and receiving of SMS messages to SIM100 GSM/GPRS through the serial port. When a text message arrives, SIM100 GSM/GPRS will send "+CMTI: "SM", N" to the serial port of ARM, where N is the SMS number. For example, in the fifth item, N is 5. After the serial port receives the SMS, the processing function first parses the content of "+CMTI: "SM", 5" to find that the ID of the received SMS is 5, and then packages it into a command of "AT+CMGR=5" and sends it to the GPRS module. After about 1~2 seconds, the module will return a confirmation data "AT+CMGR=5". After a while, the module will return a SMS with ID number 5, and its content is: "+CMGR:"RECREAD","+8613978319414","04/07/22,10:54:23+00" #13#10dX# 13#10#13#10 OK". In order to ensure the legitimacy of the control, the program first checks the legitimacy of the SMS number sent. Only the content of the SMS that matches the set mobile phone number is processed as a control command, while other SMS are blocked to prevent erroneous operations.

If the SMS is sent through the GPRS module, the ARM system first sends the control command "AT+CMGS=XXXX" to the GPRS module. After receiving the command, the GPRS module returns the message "AT+CMGS=XXXX#13#10>" and waits for the text message content to be entered. If the content to be sent is "Your Car Has Stolen!", the system program first sends this content to the GPRS module through the serial port, and then sends the confirmation command "ctl+z" to indicate that the data has been sent. After the GPRS module receives the SMS data and the confirmation command, it immediately returns the message "AT+CMGS=XXXX#13#10>#13#10 Your Car Has Stolen!#13#10" to the ARM system, indicating that the data and command sent by the system have been received by the GPRS module. Then the GPRS module sends the SMS data to the owner's mobile phone. After about 5 seconds, the GPRS module returns the feedback information to the system whether the sending is successful. If it returns "#13#10+CMGS:19#13#10#13#10 OK#13#10", it means that the sending is successful and the process ends. If "ERROR" is returned to indicate that the sending failed, the system will continue to send SMS with the same content in the next round until the sending is successful.

3.2 FLASH reading and writing technology

Since the FLASH memories of different manufacturers are different in structure and read-write operations, the burning and erasing procedures of FLASH memories are generally not universal. The FLASH used in the system is SST39LV160, which can read, write or erase any sector without affecting the data in other parts. The programming instruction of FLASH can only change the binary bit from '1' to '0', while the erase command can change '0' to '1', so the correct operation sequence must be to erase first and then program, otherwise it will cause the FLASH memory to reset, making the operation command unable to complete. When the FLASH memory is erased, the read content is all 0XFF.

The programming operation of SST39LV160 needs to follow several fixed steps. Each step is to first write the address and data command to the specific register of the FLASH memory, and then the internal programming or erasing algorithm automatically completes the programming or erasing operation. For example, in the erasing operation, the first step of the program is to write data 1 (0XAAAA) to address 1 (0X5555), the second step is to write data 2 (0X5555) to address 2 (0X2AAA), and the third step is to write data 3 (0X8080) to address 1 (0X5555). This completes the first stage of erasing the sector. The second stage is almost the same as the first stage, except that the last time is to write data 0X3030 to address 0X10000, and then the program uses a loop to detect whether the content of the sector has become 0XFF. If the content of the sector becomes 0XFF, it means that the operation of erasing the sector has been completed, and the next step can be performed to write data to the specified address of FLASH. The write operation is similar to the erase operation and also follows several fixed steps. The specific steps should refer to the technical data of the corresponding FLASH chip. After the write operation is executed, the data should be checked. If the write is successful, the next byte will be written. Otherwise, continue to wait. If the timeout occurs, exit. Since both programming and erasing require a certain amount of time, the program should determine whether the operation is completed or correct based on its internal operation detection mechanism to determine whether to execute the next step.

In our system, the system program uses the 17th sector of FLASH to store the owner's mobile phone number, starting from the first address. The usual operation procedure for this sector is: first read all the contents of the sector into SDRAM (4K in total), and then write the phone number to be written into the 11 units after the first address of sector 17. Because we do not use all of sector 17, we can skip the step of reading 4K content into SDRAM, and just need to directly write the owner's mobile phone number starting from the first address 0x10000 of sector 17.

4 Conclusion

The system adopts embedded development technology, uses S3C44B0X and GPRS communication module to develop a mobile phone-based car anti-theft system. The system can realize the remote wireless monitoring function of the car through the car owner's mobile phone. It fully utilizes the advantages of the GPRS network, can monitor 24 hours a day, low cost, and realize complete self-service. No matter where you are, you can know the specific condition of the vehicle through mobile phone query; you can also remotely control the vehicle, from opening and closing door locks, remote starting to command parking. Experiments have proved that this is a product with stable performance, high security and cost-effectiveness. The system will further realize the combination with the global satellite positioning system (GPS) and the traffic geographic information system (GIS) to realize a more powerful car anti-theft monitoring network.

The author's innovation: Using embedded development technology, S3C44B0X and GPRS communication module, a mobile phone-based car anti-theft system was developed. The system can achieve remote wireless monitoring of the car through the owner's mobile phone.