This paper introduces the performance and characteristics of AT89C2051 single-chip microcomputer, and a low-cost, high-precision, miniaturized, digital display car anti-collision alarm with its core.
The anti-collision alarm uses the ultrasonic wave and the integrated Hall element to realize the distance measurement and the speed measurement of the automobile, and uses the real-time control and data processing functions of the single-chip microcomputer to complete the control of the system. The article gives the hardware circuit principle and software design of the alarm.
With the acceleration of the pace of modern life, the frequency of traffic accidents is also increasing. In order to improve the safety of vehicle operation, this paper introduces a car-anti-collision alarm system controlled by single-chip microcomputer. The device combines the real-time control and data processing functions of the single-chip microcomputer with the ultrasonic ranging technology and sensor technology to detect the distance between the rear obstacle and the vehicle in the running of the vehicle and the speed of the vehicle, and display the distance through the digital display device, and the sound is emitted. The circuit sounds a warning based on the distance.
1 Ultrasonic Ranging Principle The principle of ultrasonic ranging is to detect the time difference T between the transmitted ultrasonic wave and the received echo by continuously detecting the echo reflected by the obstacle after the ultrasonic wave is emitted, and then find the distance S=C× T/2, where C is the ultrasonic wave velocity and is 344 m/s at normal temperature. After the speed of sound is determined, the distance can be determined by measuring the time of the ultrasonic round trip.
2 Speed ​​measurement principle The measurement of the vehicle speed is achieved by Hall integrated sensors. That is, the input shaft of the turntable equipped with the permanent magnet is connected to the rotating shaft of the wheel, and when the wheel rotates, the turntable rotates accordingly. At this time, the permanent magnet on the turntable passes through the Hall integrated sensor, thereby integrating the sensor in the Hall. The input receives a magnetic signal, and if the turntable keeps rotating, the Hall integrated sensor outputs a speed signal. It can be said that the measurement of the vehicle speed is essentially a measurement of the frequency of the speed signal.
3 Controller AT89C2051 features and features
The AT89C2051 is a low power, high performance CMOS 8-bit microprocessor compatible with the MCS-51 family of instruction sets and pins. It features 128 bytes of internal RAM, 2Kbytes of EPROM, 15 I/O lines, and 2 16 Bit Timer/Counter, 5 two-stage interrupt sources, 1 full-duplex serial port, an on-chip precision analog comparator and on-chip oscillator, low power idle and power-down modes. The operating voltage range is 4.25V to 5.5V, and the operating frequency is 12MHz.
The two 16-bit timer/counter registers T0 and T1 in the AT89C2051 can count the machine cycle when the timer is used. The count frequency is 1/12 of the oscillation frequency. When the counter is used, the external input pin P3.4/T0 can be used. And when the change from 1 to 0 occurs on P3.5/T1, the count frequency is 1/24 of the oscillation frequency.
4 hardware system design
The alarm device is composed of a control system, an ultrasonic transmitting circuit, a receiving circuit, a speed measuring circuit, an alarm circuit, and an LED display circuit, and the circuit block diagram is shown in FIG. 
The ultrasonic transmitting circuit is composed of a CC7555 time base circuit and an ultrasonic transmitting probe. The P1.7 pin of the AT89C2051 microcontroller controls the CC7555 time base circuit to generate a 40 kHz frequency signal to the ultrasonic generator, and the ultrasonic wave emitted by the ultrasonic probe is directed at the obstacle. The use of ultrasonic ranging has the following characteristics: high measurement sensitivity, strong penetrating power, fast measuring speed, large measuring angle, and detection of objects in a wide range.
The ultrasonic receiving circuit is composed of an ultrasonic receiving probe, an amplifier, and a shaper. The ultrasonic wave reflected by the obstacle is converted into an electric pulse signal by the receiving probe, and then amplified and shaped by an amplifier and a shaper, and then sent to the P3.2 pin of the AT89C2051 of the single chip microcomputer. The amplifier should use a wideband amplifier with sufficient gain and low noise to keep the pulse signal, especially the leading edge, from distortion and improve the accuracy of the ranging.
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