Design of Airport Vehicle Overspeed Alarm System Based on STC Single Chip Microcomputer

With the development of civil aviation, the number of aircraft has continued to increase, and the number of ground support vehicles has increased accordingly. In addition, the speed of airport vehicles is too fast, resulting in unsafe incidents of scratching aircraft from time to time, which directly affects the continued airworthiness of aircraft, seriously endangers the operational safety of airlines, and also causes certain economic losses. In order to reduce the occurrence of such unsafe incidents, this design uses a single-chip microcomputer to realize the vehicle's speeding alarm to remind the driver to slow down, and records the speeding situation in real time as one of the bases for evaluating vehicle drivers, so as to facilitate the management of employees.

1. System Hardware Design

1.1 System Function

The main functions implemented by the system are as follows:

(1) Press buttons to adjust the time and display the time in real time;

(2) Real-time display of vehicle speed;

(3) When the vehicle exceeds the specified speed value, the violation is saved in the serial memory in the form of data, and an audible alarm is sounded and the warning light flashes;

(4) The manager uses the IC card to read the vehicle's violation status and cancel the alarm.

1.2 Overall design of system hardware

The overall structure of the system is shown in Figure 1. It uses the STC89C52 microcontroller as the main control chip, and mainly includes power module, signal acquisition module, clock module, LED display module, button module, alarm module, AT24C64 serial memory module and contact IC card storage module. Among them, STC89C52 mainly completes the control of peripheral hardware and information processing functions; the power module steps down the 12V vehicle power supply to the 5V microcontroller working power supply; the signal acquisition module uses the TLP521 photocoupler to convert the collected high-level pulse signal into a 5V pulse signal; the clock module provides the real-time time displayed by the LED; the LED display module uses 74HC595 to drive the digital tube to display time and speed; the button module is mainly used to adjust the time; the alarm module realizes the sound alarm and flashing light warning after speeding; the AT24C64 serial memory stores the speeding information; the contact IC card memory can read the data in the AT24C64, and the alarm can be canceled after reading the data.

1.2.1 Main control module

The main control module mainly uses STC89C52 microcontroller, which has 4 parallel I/O ports, each port has 8 port lines, of which P0 port can be used as an 8-bit quasi-bidirectional I/O port when there is no external memory, and can be used as an address line/data line when an external memory is connected; P1, P2 and P3 ports can all be used as 8-bit quasi-bidirectional I/O ports, and P3 port is very different from other I/O ports. In addition to being a general I/O port, each pin has a special function. All external chips can be expanded through these ports.

1.2.2 Power Module

The power module uses the LM2596 switching voltage regulator, which is a step-down power management monolithic integrated circuit that can output a 3A drive current and has good linear and load regulation characteristics. The fixed output 5V version is selected in this system, that is, the regulator model is LM2595-5.0. The device integrates frequency compensation and fixed frequency generator internally, and the switching frequency is 150kHz. Compared with low-frequency switching regulators, smaller filter components can be used. Since the device only requires 4 external components, the design of the switching power supply circuit is greatly simplified. The schematic diagram is shown in Figure 2.

1.2.3 Signal Acquisition Module

At present, most of the speed sensors of airport vehicles use Hall sensors, whose output signals are pulse signals. The high level value of the pulse signal is basically the same as the voltage value of the vehicle power supply. It needs to be converted into a 5V pulse signal that can be collected by the microcontroller through a photocoupler. As shown in Figure 3, Signal is the actual output signal of the speed sensor. The converted signal is connected to the INT1/P3.3 pin of the microcontroller. The pulse number is recorded through the external interrupt function and converted into a speed value through calculation.

1.2.4 Clock Module

The clock module uses the DS1302 dredge charging clock chip, which contains an RTC/calendar and 31B of static RAM. It communicates with the microprocessor through a simple serial interface. The RTC/calendar provides seconds, minutes, hours, days, dates, months, and years. If the number of days in the month is less than 31, it will be automatically adjusted, including leap year correction. The clock can work in 24-hour and 12-hour systems. The 12-hour system uses AM/PM to indicate. The 24-hour system is selected in this system.

Synchronous serial communication is used between DS1302 and microprocessor. Only three lines are needed for communication, namely RST (reset), I/O (data line) and SCLK (serial clock). Vcc1 is connected to 3V backup power supply.