Abstract: Car theft cases are also on the rise as cars enter the home in large numbers. Nowadays, the car alarm devices on the market generally have the defects of high false positive rate and the inability to effectively notify the owner of the vehicle. According to the uniqueness of fingerprint and lifetime invariance, based on the existing embedded fingerprint identification system, the overall design of the automobile fingerprint alarm system is completed by using the advantages of STM32F103VC and short message service of GSM network. The experiment proves that the system design is reasonable, the scheme is highly feasible, and it has strong practical value and broad application prospects.
Keywords: fingerprint recognition; car anti-theft; single chip microcomputer; GSM; STM32
With the rapid development of the automobile market and the improvement of people's living standards, more and more cars have entered the ordinary family. Car anti-theft is particularly important and has become an important social issue that needs to be solved urgently. Most of the car burglar alarms currently on the market are retro-mounted car alarms and car alarms with electronic code keys. The built-in car alarm system mainly adopts the serial connection type. For the thieves who are proficient in the automobile circuit, the anti-theft circuit can be easily avoided by the bridging method, and the anti-theft system is like a dummy. For car alarms with electronic cryptographic keys, thieves typically steal the keys and use the remote control to quickly find a car and carry out the theft. This shows that the anti-theft means of the existing car anti-theft device is not reliable. The fingerprint identification module is used to verify the identity of the owner and assist various alarm measures to complete the design of the car burglar alarm, which can ensure the safety of the car as much as possible without changing the overall circuit of the car. Fingerprint recognition is a kind of biometric identification. It uses the uniqueness and lifetime invariance of fingerprint features to authenticate individual identity, which is extremely safe and easy to use. In this paper, the fingerprint recognition technology is applied to the car anti-theft system, and combined with the GSM wireless communication network to realize remote alarm, which effectively protects the safety of the car.
1 System structure and working principle The car alarm is mainly composed of MCU, fingerprint identification module, wireless communication module, LCD display, voice circuit, electronic password key interface circuit, keyboard, control circuit and power supply circuit. The hardware block diagram is shown in Figure 1. The MCU selects the STM32F10 3VC, an enhanced 32-bit chip based on the low-power embedded ARM CortexTM-M3 core from STMicroelectronics. It operates from 2.0 to 3.6 V. This design uses 3.3 V. With a maximum operating frequency of 72 MHz and up to 80 fast I/O ports, all I/O ports can be mapped to 16 external interrupts, and almost all ports can tolerate 5 V signals. On-chip 256 KB FLASH, 2 I2C interfaces, 2 SPI interfaces, 3 USART interfaces, 3 16-bit timers, up to 4 timers for input capture/output compare/PWM or pulse Counting channels and incremental encoder inputs, 2 watchdog timers (independent and windowed), etc. In Figure 1, "KEY-ON" is the car key position, taken from the key switch, and photoelectrically coupled to the PE10 of the STM32F103VC. The wireless communication module and the fingerprint identification module are connected to the USART1 and USART2 of the STlM32F103VC via the RS232 transceiver, MAX3232 respectively; the cryptographic key is implemented by the USB disk, the USB interface is connected to the SPI1 of the STM32F103VC; the voice circuit is connected to the SPI2 of the STM32F103VC; the 4×4 keyboard and the PE0~PE7 Connection, liquid crystal display data is provided by PD0~PD7.
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The main working principle is as follows: After the vehicle owner stops the fire, the anti-theft device enters the locked state. At this time, if the car key is not in the ON position, fingerprint recognition cannot be performed; only when the car key is in the ON position, the fingerprint recognition can be used to unlock the immobilizer and automatically ignite. In the locked state, the oil circuit and circuit of the car are cut off, and the car key cannot be ignited; if the connection between the fingerprint acquisition module and the control box is forcibly cut, or the fingerprint is forcibly ignited by the car key, the car will pass the horn, Flashing lights and wireless communication network alarms. Insert the password key in the locked state to enter the unlocked state, and perform fingerprint registration/delete, mobile number setting and emergency ignition through the keypad according to the LCD and voice prompts.
2 hardware design and implementation
2.1 USB interface circuit USB interface circuit is mainly realized by file management control chip CH376T. CH376T supports USB device mode and USB host mode, and has built-in basic firmware of USB communication protocol, firmware for processing special communication protocol of MassStorage mass storage device, SD card communication interface firmware, FAT16 and FAT32 and FAT12 file system management firmware, support common USB storage devices and SD cards. The CH376T supports two communication interfaces: SPI interface and asynchronous serial port. This design uses SPI interface to communicate with MCU data. The circuit connection is shown in Figure 2. Serial data input SDI, output SDO and clock SCK are respectively connected to SPI1_MOSI, SPI1_MISO and SPI1_SCK of STM32F103VC, interrupt request output terminal INT is connected to PC0, and chip select terminal SCS is controlled by PA1. The RESET in Figure 2 is the system reset signal, and the crystal oscillator Y1 selects 12 MHz. When the car mainly performs fingerprint registration/deletion or emergency ignition, the password key (U disk) is connected to J1 to read the password information.
2.2 LCD monitor LCD display SMG12864G3-ZK standard Chinese character and graphic dot matrix liquid crystal display module, using dot matrix liquid crystal display, can display 128 × 64 dot matrix or 4 rows × 8 Chinese characters, built-in ST7920 interface liquid crystal display control It has a GB2312 code simplified Chinese character library (16×16 dot matrix), which can be directly connected to the MCU and has 8-bit parallel and serial connection. This design is connected in parallel with STM32F103VC. The data terminals DB0~DB7 are connected to PD0~PD7 of STM32F103VC. The data/command selection RS, read/write control signal R/W and enable terminal E are connected to PB2, PA14 and PA15 respectively. . In this anti-theft device, the liquid crystal display is used to display the operation method and operation content.
2.3 Voice Circuit The schematic diagram of the voice circuit is shown in Figure 3. It consists of the ISD company's voice chip ISD4004-16 and National Semiconductor's audio power amplifier LM386. ISD4004 -16 recording and playback time is 16 min (segmentable), it uses CMOS technology, single power supply 3 V operation, including oscillator, anti-aliasing filter, smoothing filter, audio amplifier, automatic squelch and high density Level flash storage display. It has a built-in microcontroller SPI bus serial communication interface. Analog voice data can be written directly to a single location without the need for A/D or D/A conversion. The ISD voice circuit has many advantages such as natural sound quality, convenient use, single-chip storage, repeated recording and playback, low power consumption, and power failure. The LM386 operates over a wide voltage range with adjustable voltage gain. It has low power consumption, adjustable voltage supply, large power supply voltage range, few external components and low total harmonic distortion. In this design, the STM32F103VC transmits voice information to the ISD4004 via SPI2. In Figure 3, V1 and V2 are connected to the +3.3 V and +12 V power supplies via a triode. The triode is switched on and off by the PCI1 and PCI2 of the STM32F103VC. The triode is turned on to the ISD4004 only when a voice prompt is required. Powered by the LM386.
2.4 Control circuit The control circuit consists of photocurrent coupler TLP521, high current driver MC1413 and four 12 V small relays K1~K4. The suction of the relay is controlled by STM32F103VC. The relays K1 and K2 are respectively connected in series with the engine control module of the automobile and the power supply circuit of the oil pump. The function is to cut off the vehicle circuit and the oil circuit in the locked state. The relays K3 and K4 are respectively connected in the car horn and the turn signal circuit for sound and light alarm. . The relay connected to the car horn is provided with a switching switch, which can be turned on or off according to the actual situation.
2.5 Power Circuit This alarm combines power supplies of +12 V, +5 V and +3.3 V. The +12 V power supply for the audio power amplifier and control circuit is powered directly from the vehicle. The 12 V voltage is +5V voltage through the switching regulator integrated circuit LM2576-5, and the +5V voltage can be obtained by SPX1117-3.3 with +3.3V voltage.
2.6 Fingerprint identification module adopts SM-2B fingerprint recognition module, which consists of high-speed DSP processor, FPC capacitive fingerprint sensor and FLASH chip. It can store 512 fingerprint templates and has a rich instruction set search time less than 1. 0 s, the false rate is less than 0.001%, the rejection rate is less than 1%, the RS 232 serial communication interface is provided, and the communication baud rate is 57 600 b/s. The STM32F103VC controls the fingerprint recognition module through USART2. Fingerprint image acquisition and processing, fingerprint feature collection, fingerprint template entry, template storage, fingerprint comparison, fingerprint search and other functions.
2.7 Wireless Communication Module This design uses the wireless communication GSM module TC35 from Siemens. The module operates from 3.3 to 5.5 V. It can work in two frequency bands of 900 MHz/1 800 MHz and has its own RS 232 communication interface. It can easily communicate with the MCU to safely and reliably implement data, voice transmission and short message service in the system solution. In the circuit, the TC35 communicates with the USART1 of the STM32F103VC through the MAX3 232. When an alarm occurs, the alarm will automatically send an alarm message to the owner's mobile phone. This enables remote alarms to be implemented in real time, reliably and quickly.
3 software design System main program flow chart shown in Figure 4.
In the locked state, when the car mainly performs fingerprint registration/deletion or emergency ignition, access the password key, and the STM32F103VC generates the SPI chip select signal of the CH376T chip in its PA1 through the keyboard, which is active low, and then sends a word according to the SPI output mode. The data of the section, with a delay of 1.5μs, receives one byte of data from the CH376T. After waiting for the SPI interface to be idle, the MCU continues to receive data from the CH376T until the MCU disables the SPI chip select. Next, password matching is performed on the read data. When the password is correctly matched, the setting state can be entered, and the owner can operate according to the voice and the LCD prompt, and the operation returns to the locked state after the operation ends. If the password is not matched correctly, the corresponding alarm signal will be issued and the circuit and oil circuit will be cut off. If you do not set it, when you insert the car key and hit the “ON†position, you can collect and match the fingerprints. If the matching is correct, it can be automatically ignited (the car key can be ignited again when the ignition fails). If the fingerprints match incorrectly, the corresponding alarm will be issued. Keep the circuit and oil circuit disconnected.
4 Conclusions This paper uses the enhanced 32-bit low-power single-chip STM32F103VC, fingerprint recognition technology and wireless communication GSM technology to design a car anti-theft system, which uses the uniqueness of the biometrics of human fingerprints to control the circuit, oil circuit, etc. of the car through fingerprint recognition. In order to achieve the purpose of theft. The non-reproducibility and complexity of living fingerprints can achieve the characteristics of anti-decoding, and solve the problems of the current widely used wireless remote control methods such as over-the-air interception and illegal acquisition of electronic keys. GSM technology adds a human defense function that enables remote alarms over a wireless network. The design of the system effectively compensates for the shortcomings of the single anti-theft circuit and ensures the safety of the car.
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