Taxi, online car-hailing and other vehicle services, as one of the ways for the public to travel, are convenient for travel but also bring safety hazards. In recent years, the rapid development of online car-hailing, but with the frequent occurrence of car safety incidents, with the improvement of user security awareness, the personal safety of drivers and passengers has now become the focus of social attention [1]. When the safety of the occupants is threatened, the driver or passenger can take the initiative to call the police or call for help to report to the police. However, when the victim’s behavior is restricted and it is inconvenient to call, this alarm method has a low success rate and is difficult to effectively protect the ride. Safety. Therefore, the design of effective alarm methods and devices has become a new research focus.
Existing taxis that enable global positioning system (GPS) for positioning and the “one-key alarm” application for alarming, due to various reasons, make the GPS system useless. In critical situations, the buttons of the GPS alarm system cannot truly realize hidden alarms. Security is still not guaranteed [2]. Didi Chuxing has set up a “one-key alarm” module on the driver and passenger application software (APP) clients, but this method requires the driver or passenger to click the corresponding alarm function on the APP to call the operator to intervene. The alarm method is still very passive . Based on the shortcomings and limitations of existing vehicle safety alarm methods. In this paper, a more effective vehicle hijacking alarm system is designed and studied.
Overall system design
The main purpose of the car hijacking alarm system design is that when the driver or passenger encounters danger during the ride, the alarm system can be used to quickly call for help, get out of danger as soon as possible and ensure personal safety. The system has functions of alarm, recording for evidence, LCD display, buzzer for help, and smoke eruption. It is composed of six parts: core module, power supply module, sensor module, alarm module, rescue module, and recording forensic module. In this alarm system, after an external force acts on the sensor module, the pressure sensor in it sends a signal to the core module. After receiving the signal from the sensor module, the single-chip microcomputer located in the core module processes and activates the alarm system in real time, and Send corresponding control signals to the alarm module, rescue module and recording forensics module to drive the relevant execution devices to work.
System hardware design
2.1 Core module
The core module mainly performs system control functions, and completes its communication with other functional modules through the serial port. In this design, SPCE061A single-chip microcomputer is used as the control chip of the system. It is a 16-bit microprocessor chip developed and launched by Sunplus Technology. It has high integration and superior performance, such as low power consumption and fast processing speed. And other advantages, it can process complex digital signals very easily and quickly. In addition, SPCE061A has an audio conversion channel and an automatic gain control circuit (AGC), which can complete voice playback after connecting to a large circuit. It is an economical and practical single-chip microcomputer that is especially suitable for voice recognition [3].
2.2 Sensing module
The sensing module is mainly composed of a pressure sensor and an amplifying circuit, which is used for pressure detection and amplifying of the received signal. Among them, the pressure sensor is a component that is sensitive to weight and adopts the principle of bridge balance. Among them, the elastic element produces elastic deformation under the action of pressure to form a voltage signal, and the sensor transmits the voltage signal to the amplifying circuit to further amplify the signal [4]. The LM386 operational amplifier circuit can work under single power supply and dual power supply conditions, and has a wide voltage operating range. The LM386 amplifier circuit is used in the design of this system.
When the alarm person presses the start button of the alarm system, the pressure signal is sensed by the pressure sensor in the module and converted into an electrical signal. After passing through the LM386 amplifier circuit, the electrical signal is amplified and processed, and then the core module is driven, and the SPCE061A single-chip microcomputer sends out The instruction activates the alarm module and makes the alarm system work.
2.3 Alarm module
The alarm module is divided into three subsystems: 110 alarm, LCD screen alarm, and buzzer alarm according to different functions. The specific design is as follows.
1) 110 alarm
The realization of the 110 alarm function is based on the GSM module. The high-performance GSM module TC35i introduced by Siemens is used to send short messages. TC35i GSM module has the advantages of low power consumption and high reliability, supports RS232 serial port, and provides functions such as short message service. It is controlled by AT commands, and the data interface can transmit instructions and data in both directions [5]. The function of designing this part of the module in the system is mainly reflected in that when the pressure sensor obtains the information and transmits it to the core module, the SPCE061A microcontroller controls the TC35i GSM module to send a help message to the 110 to alarm.
In addition, the system also uses GPS and Beidou dual positioning[6] to provide police officers with information on the latitude and longitude of the vehicle’s location, which facilitates quick positioning of the police officers and improves rescue efficiency.
2) LCD screen and sound alarm
The realization of the alarm function of the LCD screen mainly relies on the on-board LCD screen. When the signal from the core module is received, the LCD screen is driven to display a distress signal such as “SOS” to attract the attention of the surroundings to help rescue. The audible alarm function is realized by a buzzer device. After the buzzer device receives the corresponding instruction, the driver will sound and use the sound to attract the attention of the surrounding drivers and pedestrians, thereby playing a deterrent effect.
In this alarm module, both the 110 alarm and the LCD screen alarm are designed as first-level alarm systems. As long as the user activates the on-board alarm system, the two subsystems in the alarm module will be turned on in real time to complete the concealed alarm. After a few minutes, if no rescue has been obtained, the second level alarm will be activated, that is, the buzzer will alarm. Turning on the buzzer can quickly attract the attention of nearby people and strive for rescue.
2.4 Rescue module
A smoke device is mainly designed in the rescue module, which is composed of optocoupler devices, relays, smoke sprayers and other components. After starting the alarm, the SPCE061A in the core module uses its IOA15 pin to drive the optocoupler device to work, the relay coil part is energized, the contact switch is closed, and the smoke discharge device is turned on [5]. The purpose of setting up this module is to confuse the robber into thinking that the vehicle is malfunctioning, and to interfere with the robber’s actions through smoke, so as to provide the victim with a chance to save himself or himself.
2.5 Recording module
The function of the recording module is to perform live recording and retain evidence. The hardware circuit of this module is mainly composed of audio input and audio output [5].
1) Audio input circuit. The recording module is composed of electret microphone and the built-in AGC circuit of the single-chip microcomputer. The working principle is: the analog audio signal is converted into an electrical signal through an electret microphone, after filtering out the DC component, the built-in amplifier of the microcontroller is used to amplify the audio signal, and the AGC circuit is driven to track and monitor the signal level output by the amplifier at any time, and adjust it in time. Amplifier gain to ensure the best level to enter the A/D circuit.
2) Audio output circuit. The speaker and LM386 amplifier circuit form an audio playback module. The working principle of this part is: read the digital signal recorded by the recording module and stored in the register, and use the built-in DAC in SPCE061A to restore the digital audio signal to analog audio signal. After inputting the power amplifier circuit, the analog audio signal is obtained Amplify to drive the horn to sound.
3 System software design
The car hijacking alarm system is powered on after the user presses the alarm button, and the system starts by itself, that is, the alarm module, rescue module and recording module start to work.
This paper designs a multifunctional car hijacking alarm system with 110 alarms, LCD screen alarms, sound alarms, smoke eruptions, and recording evidence collection. The article first introduces the overall structure of the system and the functions that need to be implemented, and then elaborates on the two aspects of hardware and software implementation. The car hijacking alarm system designed in this article is suitable for taxi or online car-hailing drivers and passengers encountering danger. It has a variety of ways to call for help, so it can ensure personal safety when danger comes as much as possible.