This article refers to the address: http:// 2 system hardware design The system hardware circuit is mainly composed of the following parts: relay module, microprocessor module, wireless communication module, GSM module, power module, sensor module. The system hardware structure is shown in Figure 2. 2.1 Microprocessor module The system microprocessor module adopts STC89C52 series single-chip microcomputer as the core, which mainly completes system control and signal processing functions. This single-chip microcomputer is a new generation of super anti-interference/high-speed/low-power single-chip microcomputer introduced by Hongjing Technology. The instruction code is fully compatible with the traditional 8051 single-chip microcomputer. The 12 clock/machine cycle and 6 clock/machine cycle can be arbitrarily selected. The latest D version Internally integrated MAX810 dedicated reset circuit; operating frequency range: O ~ 40 MHz, equivalent to ordinary 8051 0 ~ 80 MHz, the actual operating frequency can reach 48 MHz; on-chip integrated 11280 B / 512 B RAM; ISP (in the system programmable ) /IAP (programmable in the application), no special programmer/emulator is needed, the user program can be directly downloaded through the serial port (P3.O, P3.1), and the 8KB program can be completed in 3 s, suitable for large-scale product development. . 3 system software design According to the working principle, the program design mainly consists of the following three modules: start module, control module, monitoring module. The startup module performs the necessary settings on the components; the control module receives the user instructions, assigns the work, and performs corresponding processing; the monitoring module monitors the sensors in real time, and sends a short message alarm after being triggered. According to the format of the AT command " 4 Conclusion Compared with the existing car alarm system, the main functions and advantages of the system are as follows: Wire female ,Wire Lugs Ring Terminal,Quick Connect terminal ,Connector Terminal Block Dongguan Andu Electronic Co., Ltd. , https://www.idofuseholder.com
0 Introduction With the rapid development of the economy, the number of cars in the society has increased significantly. At the same time, the number of car theft cases has also increased significantly year by year. In fact, the car can completely make the thief inorganic by installing an alarm. However, the early car alarms had a single function, the false alarm rate was relatively high, the noise was large, and sometimes the wind and rain would also alarm, but the alarm effect was not achieved when the danger was actually encountered.
At present, there are many types of alarms, which can be mainly divided into audible alarms, wireless alarms and GPS positioning alarms. Commonly used audible alarms generally sense abnormal vibrations of a protected object (such as a car or a safe) through a vibration sensor, and then drive a high-power audible alarm. The disadvantage of the alarm mode is that the alarm distance is short, noise pollution to the environment, and the alarm is easily disassembled. Or destroyed. The GPS alarm has high cost of network access, small monitoring range and poor stability.
Based on GSM network car alarm system, it integrates GSM network, wireless remote control and digital signal processing technology. It adopts the latest modern technology and has two-way communication, simple installation, convenient use, wide application and high reliability. It can be widely used. In all types of car burglar alarm.
1 System working principle and structure The working principle of the system is as follows: When the car is stolen, the vibration of the vehicle body is detected by the sensor, and the system microcontroller generates alarm information through system analysis and processing according to the signal detected by the sensor; The GSM module is controlled by the micro controller to dial the user's phone and send a text message to the alarm. The working principle is shown in Figure 1. 
2.2 GSM module The system GSM module uses SIM300C dedicated communication module, which is mainly responsible for SMS and telephone communication between the alarm and the user. This module is embedded with TCP/IP protocol and AT command control, which is very convenient for data transmission. The module has the following features:
(1) Power supply voltage: 3.4 ~ 4.5 V;
(2) Coding schemes: CS-1, CS-2, CS-3 and CS-4;
(3) SMS message support MT, MO, CB, Text and PDUmode; SMS storage: SIM card;
(4) Support 1.8 V, 3 V SIM card.
The SIM300C delivers high-speed transmission of voice, SMS, data and information in small size and low power consumption to meet system design requirements.
2.3 Wireless Module The system uses the wireless receiving module 3310A for short-distance data transmission between the remote control and the alarm to realize the start and stop functions of the alarm.
The 3310A receiving module is a superheterodyne receiving module with a high cost performance directly on the PCB. It has the characteristics of small size, no debugging, no peripherals, stable performance, etc. The chip contains RF amplifier, mixer and local. Oscillator, IF amplifier, filter and limiter comparator, output as data level signal, can be directly decoded to standard decoder or CPU, frequency is 315 MHz and 433.92 MHz, suitable for ASK mode transmitter module and remote control Handle matching.
Product performance and advantages:
Receive frequency: 315 MHz, 433 MHz (without debugging); Operating voltage: 2.5 to 6 VDC (typical 5 V); Operating current: 2.5 mA/3 V, 4.5 mA/5 V; Receiver sensitivity: -90 dBm (1.8 μV); receiving mode: ASK; data rate: 4.8 Kb/s; demodulation filter bandwidth: 5 Kb/s; operating temperature: -40 to +80 °C. Its peripheral circuit is shown in Figure 3. 
3.1 Startup Module The startup module consists of two parts: initializing the STC89 microcontroller and initializing the SIM300C communication module. First, the microcontroller's timers and interrupts, serial ports, system variables, etc. must be initialized.
The microcontroller has a fast processing speed and a slow serial port speed, which brings a great hidden danger to the real-time monitoring of the alarm. The microcontroller cannot wait to receive the entire data. In order to improve the real-time monitoring capability, the communication module introduces a cache, temporarily stores the incomplete information in the cache, and processes the information after the information is complete. The cache structure adds a read pointer and a write pointer to perform read and write operations on the cache, thereby ensuring that the data can be read while the data is being read, and the two pointers do not interfere with each other. Initialize the SIM300C communication module to start the SIM300C by pulling down the IGT, and send the AT command through the serial port to perform the necessary initialization settings. Table 1 is an AT command used to initialize the SIM300C. 
The system uses the information prompt method to read the information content. Finally, the caller ID is set, mainly to confirm the identity of the user, and it is convenient for the user to start and close the monitoring function. The setting of the whole startup code is mainly to prepare for the subsequent work.
3.2 According to the programming requirements, the control module only needs to extract the called number and user data (Unicode string). The called number is used to confirm whether the owner's mobile phone number is not used. Cache, continue to monitor, after confirmation, according to the content of the user's short message, make the appropriate settings.
The function of the "set" command is to modify the mobile phone number of the owner in the alarm; the "modify" command is to modify the password in the alarm, and the function of the password is to prevent anyone from modifying the alarm mobile number. Send the corresponding short message content to complete various settings:
(1) "Start" short message, start the alarm.
(2) "Close" the short message and turn off the alarm.
(3) "Setting" a short message to replace the mobile number with control.
(4) "Modify" the short message and modify the login password.
(5) "Query" short message to query the working status of the alarm.
3.3 Detection Module This module consists of a high-precision vibration sensor. After the module is triggered, a low level signal is sent to the microcontroller.
The controller detects a low level signal and sends a text message to the owner's mobile phone for an alarm. It can be seen from Fig. 4 that after the completion of the message, when the low level has not yet jumped to the high level, the micro-controller detects that the monitoring device is at a low level, and repeatedly sends a message. In order to solve this problem, the alarm information is sent to continue to detect the monitoring device, and when it is high, it jumps out, thus avoiding information retransmission and enhancing the stability of the system. 
(1) Due to the use of special high-precision adjustable vibration sensor detection method, when the vibration generated by the touch of the car produces an alarm signal, the accuracy of the sensor is adjustable, which can effectively avoid the defect that the existing automobile vibration alarm is prone to false alarm.
(2) The alarm system is equipped with a mobile communication module and intelligent control using a single-chip microcomputer. When an alarm signal is generated, the mobile communication module automatically dials the owner's mobile phone or sends a short message to the owner's mobile phone, so that the alarm signal can be transmitted to the mobile communication service. Anywhere covered, it overcomes the shortcomings of the signal transmission distance of the ordinary alarm system. After receiving the alarm signal, the owner can take necessary measures, such as telephone alarm, call to inquire, personally check and so on.
(3) Compared with the existing alarm device, the alarm device can dial the mobile communication telephone number included in the alarm SIM card by using the owner mobile phone, and automatically cancel the alarm after the two numbers match. You can also activate or deactivate the alarm using the remote control.
(4) The alarm system based on GSM network solves the problems of high GPS access cost, small monitoring range, poor stability and general car alarm distance limitation.