Design of car anti-theft system based on GPRS and GPS
With the rapid development of China's economy, more and more families are buying cars, but with it comes an increase in car theft cases. Although most vehicles are currently equipped with anti-theft systems, they are generally sound and light warnings. Once the distance between the person and the vehicle is too far, the owner will not be informed of the vehicle ’s theft in time, thus losing many opportunities to report the alarm. If the owner has a GSM mobile phone that sends and receives short messages, the anti-theft system can realize real-time alarm, and GPS can determine the location information of specific vehicles, which is convenient for finding lost cars.
1 Core controller part
1.1 Introduction to STR710F microcontroller
STR71X is an on-chip microcontroller with integrated Flash and RAM. It is based on the high-performance ARM7TDMI core, with rich peripherals and enhanced I / O functions. All devices in this series include on-chip high-speed single-voltage Flash memory and high-speed RAM memory. Due to the embedded ARM core, STR71X is compatible with all ARM tools and software.
1.2 Overall structure of STR710F microcontroller
The overall structure of the STR710F microcontroller is shown in Figure 1. The internal bus and two APB buses tightly connect the system-on-chip and peripheral resources. Among them, the internal bus is the main system bus, connecting the CPU, memory and system clock, etc .; the APB1 bus is connected to the high-speed peripherals, and the APB2 bus is connected to the system general peripherals and interrupt control. The I / O port includes three 16-bit ports, P0, P1, and P2, and other peripheral interface pins are multiplexed with the pin functions of the I / O port. This processor supports the CAN bus function, which has very important applications in automotive electronics.
2 Introduction to GPRS Modem
The development system selected Wavecom's pj_q2403 new generation GSM / GPRS dual-mode module, with a compact design, fully compatible with the previous generation TC35 product, providing users with a simple, embedded wireless GPRS connection. The module's GPRS permanent online function provides the highest data transmission rate, and has a small size and low power consumption. It can provide data, voice, SMS, and fax functions, and can be widely used for remote sensing measurement record transmission, remote information processing, and telephone. As an ideal solution for high-speed data transmission, this module is widely used in POS terminals and scanners, security systems, remote telemetry and information processing systems, tracking management systems, traffic control and navigation systems, portable control devices, GPRS; supports EGSM900 / GSM1800 dual frequency, support GPRSClass8 / GPRSClassB, AT command direct control; the highest rate in CSD state is 14.4 kbps, the highest rate in GPRS state is 86.5 kbps.
2.1 GPRS service
GPRS was proposed by British BT Cellnet as early as 1993, and is one of the contents of the GSM Phase2 + specification. It is a GSM-based mobile packet data service that provides users with mobile packet IP or X.25 connections. GPRS superimposes a new network on the basis of the existing GSM network, and at the same time adds some hardware devices and software upgrades to the network, forming a new network logical entity, providing end-to-end, wide-area wireless IP connection. In layman's terms, GPRS is a high-speed data processing technology. It is based on packet switching. Users can use various high-speed data services under mobile state through GPRS, including Internet browsing by E-mail. GPRS is a new GSM data service, providing a connection between mobile users and data networks, providing high-speed wireless IP and X.25 services to mobile users; due to the use of packet switching technology, each user can occupy multiple Wireless channel, the same wireless channel can be shared by multiple users, resources are effectively used. The extremely fast transmission of 160 kbps with GPRS technology can almost allow wireless Internet access to achieve the effect of the company's ISDN, enabling you to carry the Internet with you.
2.2 GPRS connection GPRS principle
The command interface provided by GPRS conforms to the GSM07.05 (interface between data terminal equipment and data circuit terminal equipment for short message service and cell broadcast service) and GSM07.07 (AT command system for GSM mobile equipment) specifications. The ARM7 processor establishes a communication link through the AT command issued by the serial port. The command format of the AT command set starts with AT. The following are several AT commands commonly used to connect to the GPRS service.
After the above command is successful, the communication service with GPRS is established, and the communication link with the data center is established, and the data of the user data device can be sent and received at any time.
3 Composition and function of automobile anti-theft system
Automobile anti-theft system is mainly composed of ARM7-based development board, GPRS module, GPS module and detection circuit.
3.1 Signal acquisition
The signal acquisition system is to use the sensor detection circuit to feel the effect of the outside world on the car, and to collect and detect the effective signal. Generally, the vehicle is damaged and stolen in the following forms: ①The body, doors, and windows are hit or knocked; ②The doors, hood, and rear cargo door are abnormally opened; ④The car thief intrudes into the car, or opens the vehicle with the stolen key; ⑤Drags the vehicle or lifts the vehicle off the ground without releasing the anti-theft function.
This system mainly detects abnormal vibrations (such as using a fake key to open a car door or forcibly knocking on a car door) to detect the vibration generated by the car body, and then generates an electrical signal to the system. At this time, the azimuth signal determined by the GPS can transmit specific vehicle position information to the owner or the center console through the GPRS module, which is helpful for the owner to find the missing vehicle. At the same time, through the remote control, the door can be opened and closed, arming, disarming, opening the trunk, controlling the car search, and controlling the vibration alarm function, and the owner can leave the warm prompt sound when leaving the car. When it is illegally started or damaged, the car control CPU sends text messages and calls to the car owner and the service center, the car alarm sounds a voice alarm, and the four turn signals continue to flash, while the car can automatically shut down.
3.2 Monitoring Center
The monitoring center is designed as a website, and its computer can be connected to the Internet through GPRS Modem as a server or data terminal. Regarding the resolution of the IP address problem, you can apply for a dedicated IP address or send it to the other party via short message after obtaining the IP address online. After the anti-theft device finds an emergency, it connects to the computer in the data center on the Internet through the GPRS network. In the process of data transmission, both parties must know the other party's IP address to exchange data, and both parties' IP addresses should be directly accessible on the Internet. This requires the IP address of the control center computer to be independent on the Internet, not the IP address of the local area network.
In general, there are many types of connection between the computer of the control center and the Internet. The IP obtained when dialing up the Internet is dynamic, which is different every time. This requires that the IP of the computer of the data center be notified to the anti-theft device system before communication. You can use the short message service to send the IP of the data center computer to the SIM card in an agreed form, and the system reads the IP value from the SIM card. If the IP of the data center computer is fixed, it can be written when the anti-theft device system is initialized.
3.3 Vibration detection
The interface circuit of the vibration detection sensor is shown in Figure 3. The timer of the STR710FZ2T controller has a capture function. Use TImerA's capture pin (this pin is connected to R2), first set to falling edge capture; after entering the falling edge capture interrupt, record the falling edge capture time as the start of calculating the low time; then set to rising edge capture , Enter the capture interrupt again to calculate the low-level duration. Since this time may exceed the time of the clock overflow, it is necessary to record the number of overflows in the overflow interrupt, which can be calculated when calculating the low-level time width.
When the low-level time width is obtained, it can be judged whether an alarm is needed according to the time width. If the time width is too narrow, it will be ignored; if the low-level time width enters the alarm range, weighting will not be performed immediately, but the weighted value will be accumulated, and if the weighted sum reaches the alarm limit, the alarm will Turn off the capture interrupt. After this treatment, the false alarms that often occur in anti-theft systems in the past will be greatly reduced.
3.4 Hall sensor detection
The application principle diagram of a single Hall switch device is shown in Figure 4. Due to the extremely low power consumption of the A3210ELH, the maximum operating current is less than 3 mA and can be driven directly by the I / O port of the microprocessor. At the input end near the chip A3210ELH, the bypass capacitor C1 should be set to 0.1μF, which can reduce the influence of external noise and internal chopping on the sensor signal. The output bypass capacitor C2 provides energy for the output transition signal, and R1 is used for protection in between.
4 System software design
The software part is written in the embedded C language of the microcontroller, as shown in Figure 5. The software flow chart focuses on the vibration (anti-theft) detection part and the preparation of GPRS communication.
5 Conclusion
In summary, the automobile anti-theft monitoring system based on GPRS and GPS is a brand-new automobile anti-theft device using the increasingly perfect global mobile communication network and ARM control technology. After mastering this technology, it is easy to apply it to building equipment safety monitoring, vehicle monitoring and dispatching, field data collection and monitoring, water conservancy and water regime monitoring, environmental remote monitoring, heating system monitoring, water pipe network monitoring and pipeline gas Where monitoring does not require real-time data on site. Its biggest advantage is the use of public mobile communication network, which can quickly build the network, reliable communication and less investment. With the development of China's mobile communication network, its application prospects are good.
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