1 Introduction
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With the rapid development of the automobile industry, more and more people have private cars, and there will be more and more traffic problems. Among them, safe reversing is one of the most worrying issues for drivers who have just taken a driver's license or a car that is too old. If you don't pay attention, you will not only bring losses to yourself or others, but also cause unnecessary quarrels. In response to the above problems, we have designed a reversing anti-collision alarm that can inform the driver of the obstacles around by the sound or more intuitive display, and relieve the trouble caused by the driver's parking and starting the vehicle before and after the vehicle. It also helps the driver to remove the defects of blind spots and blurred vision, which improves safety.
2. Overall structural design
The system is mainly composed of SPCE061A single-chip microcomputer, ultrasonic sensor and distance warning module. The overall structure of the system is shown in Figure 1.
2.1 Control core unit
SPCE061A is a high-performance, low-power 16-bit microcontroller developed by Taiwan's Lingyang Technology Co., Ltd. It has up to fourteen interrupt sources and is a 16-bit microcontroller with high cost performance. The SPCE061A's instruction set uses a reduced instruction set with short execution time and the ability to process complex digital signals quickly. At the same time, SPCE061A has 8 10-bit precision ADCs, one of which is an audio conversion channel, and has built-in automatic gain circuit; two 10-accuracy DACs only need external amplifier circuit to complete the voice playback, which provides voice reminder Convenient hardware conditions.
2.2 Sensor module
The module consists of two parts: an ultrasonic transmitter and an ultrasonic receiver. The main purpose is to complete the transmission and reception of ultrasonic waves, in which the collected electrical signals are amplified and compared, so that the SPCE061A MCU can obtain more accurate data.
2.2.1 Ultrasonic generator
The ultrasonic generator uses a piezoelectric ultrasonic generator. Piezoelectric ultrasonic generators work with the resonance of a piezoelectric crystal. It has two piezoelectric wafers and a resonant plate. When its two poles are applied with a pulse signal whose frequency is equal to the natural oscillation frequency of the piezoelectric wafer, the piezoelectric wafer will resonate and drive the resonator plate to vibrate, generating ultrasonic waves. The internal structure of the generator is shown in Figure 2. The ultrasonic generator is connected to pin IOA1 of SPCE061A and controlled by software to control the occurrence or not.
2.2.2 Ultrasonic Receiver
The ultrasonic receiver includes an ultrasonic receiving probe and a signal amplification unit. The ultrasonic receiving probe must correspond to the model of the transmitting probe, mainly because the frequency should be consistent, otherwise the receiving effect will be affected by the inability to generate resonance, or even unacceptable.
Since the electrical signal converted by the probe is very weak, it must be amplified by the amplifier circuit. The signal received by the ultrasonic receiver can be directly input into the microcontroller through the IOA2 pin of the SPCE061A microcontroller, which simplifies the hardware circuit of the system.
2.3 Distance warning module
The module mainly includes: voice, LED dot matrix and reminder indicator light. When the driver turns the vehicle gear, the triggering condition is triggered to start the system. The LED dot matrix shows the distance between the tail and the obstacle. When the distance from the obstacle is less than the preset range (1m, 0.5m, 0.25m), different "BI, BI" alarm sounds (normal, faster, rush) are issued, and the corresponding reminder indicator starts. Blinking, the degree of flicker corresponds to the alarm sound, in order to enhance the effect of the reminder.
3. Software design
3.1 Main program
The main program mainly completes the initialization of the system, controls the transmission and reception of the trigger pulse signal, calculates the distance between the tail and the obstacle, and determines whether the measured distance is within the corresponding range to drive the display circuit and the sounding circuit. The main program flow is shown in Figure 3.
3.2 Ultrasonic ranging
The algorithm is slower than the speed of the car when reversing. Compared with the speed of sound, the car can be considered to be stationary, so the influence of the Doppler effect can be ignored in the system. Ultrasonic ranging is the use of its reflection characteristics. The ultrasonic transmitter continuously emits ultrasonic waves of a certain frequency and reflects after encountering obstacles. When the ultrasonic receiver receives the reflected signal, it converts it into an electrical signal, and measures the time (T) of the transmitted wave and the reflected wave, according to S. The distance (S) can be obtained by =C×T/2. Where C is the ultrasonic wave velocity and is taken as 344 m/s at normal temperature.
4 Conclusion
The system utilizes SPCE061A's powerful real-time control and data processing capabilities, which significantly improves reliability and accuracy. In addition, it is characterized by simple structure, reliable operation and small measurement error. The system can visually display the distance between the rear and the obstacle through the LED dot matrix, which provides convenience for the driver. When the obstacle distance is less than the alarm distance set by the system, the system lights up the reminder light and sends a synchronous voice prompt to prompt the driver to brake to prevent the car from colliding or scratching, which makes the system highly practical.
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