Design of automobile anti-collision alarm system based on single chip microcomputer

With the continuous progress of social economy and the rapid development of high technology, cars have become people's ideal means of transportation in daily work and life. While cars bring convenience to people, they also cause frequent traffic accidents, which have caused casualties and economic property losses. Therefore, the safety of car driving has become the focus of people's attention. Automobile collision safety technology is the most difficult and core part of automobile safety technology. Analysis of highway traffic accidents shows that more than 80% of car accidents are caused by drivers' inadequate reaction, more than 65% of vehicle collisions are rear-end collisions, and the rest are side collisions. In order to reduce the occurrence of car accidents and provide a sense of security to users who own cars, it is of practical significance to develop a simple, reliable, easy-to-use, and automatic distance detection safety system that can send an alarm to the driver when the car is less than the safe distance from the obstacle. Since ultrasonic detection has the advantages of fast and accurate detection, this design uses ultrasonic detection chips to realize the collision warning function.

1 Hardware Design of Automobile Anti-collision Alarm
According to the product cost performance and actual needs, the intelligent ultrasonic distance measurement integrated circuit chip SB5027 developed by Zhongyi Electric Measurement Research Institute is selected. It adopts CMOS manufacturing process, has a comparator, a standard 40 kHz ultrasonic generator and an echo response pulse receiver, and integrates dynamic digital display information output, operation keyboard, data storage, parameter setting and other functions. When SB5027 is used for distance detection, it has the following characteristics: dynamic digital tracking display; the upper limit, middle limit, lower limit and other parameters of the distance can be set; the alarm permission parameters such as distance, time, timing, etc. can be set; the maximum range and minimum resolution are set by the user; support value-added distance measurement function. The system hardware structure design is shown in Figure 1. The system consists of ultrasonic transmitting circuit, ultrasonic receiving circuit, keyboard display circuit, core function chip, auxiliary circuit (reset circuit and crystal oscillator circuit) and alarm circuit.

1.1 Principle of ultrasonic ranging
The basic principle of ultrasonic ranging is basically the same as that of sonar echolocation. The ultrasonic generator continuously emits 40 kHz ultrasonic waves, which are reflected back when encountering obstacles. The ultrasonic receiver receives the reflected wave signal and converts it into an electrical signal. By measuring the time difference T between the transmitted wave and the received reflected wave, the distance can be calculated:
S = (1/2) CT
, where C is the ultrasonic speed of sound, and:

Where: y is the adiabatic volume coefficient of the gas (1.4 for air); p is the gas pressure (1.013×106Pa at sea level); gadolinium is the density of the gas (1.29 kg/m3 for air).
For 1 L of air, the mass is m, the volume is v, and the density p=m/v.
Therefore:

Where: R is the molar gas constant; T is the absolute temperature. [page]

Since y, R, and m are all known constants, the speed of sound C is only related to temperature. If the temperature T remains constant, the speed of sound in the air has nothing to do with air pressure. At 0°C, C0 = 331.45 m/s. For any temperature, we have:

1.2 Sound and light alarm, wireless signal transmission and receiving circuit design The
automobile anti-collision alarm detection uses ultrasonic sensors. The ultrasonic sensor consists of an ultrasonic transmitting circuit and an ultrasonic receiving circuit. The ultrasonic transmitting circuit consists of a Schmitt trigger, a transformer, and a transmitting sensor T probe. Since the SB5027 has a standard 40 kHz ultrasonic generator inside, its internal signal (lead out from the pin SONICOUT) is directly led, but the signal is weak, and the signal must be amplified in the transmitting circuit. This signal is connected in series through two Schmitt reverse triggers, and the NPN transistor VT is turned on through a voltage divider resistor, and the voltage pulse signal at the output end is fed back to the transformer. The voltage signal is increased by the step-up transformer to drive the transmitting type T40 sensor to emit 40 kHz ultrasonic waves. The circuit diagram is shown in Figure 2.

Ultrasonic signal reception and processing is one of the key technologies of the distance measurement system. Since the ultrasonic receiving circuit amplifies the weak signal output by the probe to a sufficient level to drive and control the subsequent circuit, the receiving circuit mainly solves the diffuse reflection phenomenon on the surface of the receiving signal. Therefore, the receiving circuit mainly solves the stability of the receiving signal, that is, the automatic gain control problem of the receiving signal. Since the transmitting signal is relatively weak when it contacts the surface of the object, and the distance to be measured causes uneven amplitude of the reflected signal. In order to eliminate the influence of the above defects, the receiving circuit should have signal amplification and automatic gain control functions. The chip LM331 is selected in the design to complete the voltage/frequency conversion. The ultrasonic receiver R converts the received reflected wave into voltage after filtering through capacitors and resistors through LM331, and then amplifies and shapes the voltage converted by LM331 through two reverse Schmitt triggers in series and sends it to the ECHO IN end of SB5027. The circuit diagram is shown in Figure 3.

When the alarm circuit exceeds the range limit, the BELLOUT terminal of SB5027 outputs a high level to turn on transistor VT1, connect the alarm to the power supply and sound the alarm. The circuit diagram is shown in Figure 4.

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2 Software system design
The alarm software design flow chart is shown in Figure 5.

After the system is powered on, the main program completes the initialization work, including register initialization, etc. When the car is in operation, the alarm devices placed in front and behind the car will collect the on-site signal and transmit it to the SB5027 microcontroller. The microcontroller processes, calculates and compares the received signal. Under normal circumstances, the alarm will not sound an alarm; if it exceeds the lower limit, an audible and visual alarm signal will be generated to remind the driver to take corresponding measures.

3 Conclusion
The car anti-collision alarm designed in this paper makes full use of the internal resources of SB5027 to perform data processing and time control functions, so that the system works in the best state and improves the comprehensive response sensitivity of the system. The alarm is timely and the anti-collision function control is realized. Practice has proved that the use effect of this system is better than other alarms, and it has the characteristics of small size, easy use and simple operation.