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Ultrasonic reversing collision avoidance system

In Electronic Infomation Category: U | on April 13,2011

Abstract: ATMEL Corporation AT89C51 MCU receives the distance ultrasonic sensor signals, according to the principle of ultrasonic distance measurement, real-time signal is sent to MCU, MCU distance calculation, display, alarm, when there are obstacles in the detection range Time and TPC8111 datasheet and distance of the obstacle is less than the alarm when a certain frequency of light-emitting diode flashes and TPC8111 price and the buzzer alarm prompts and TPC8111 suppliers and displays the distance between obstacles. Proven, this system realizes the function of ultrasonic reversing collision avoidance system, and the more stable the system is real time, the error is relatively small distance.

0 Introduction

With the increasing number of cars, road congestion, frequent traffic accidents, to people living with a lot of inconvenience, safety became the first element of the design and vehicle collision avoidance system demand urgent. Therefore, the design which uses ultrasonic ranging, collision avoidance through the MCUs reverse warning system, the main consideration of its design is simple, easy to operate.

1 ultrasonic ranging principle

Ultrasonic frequencies higher than 20 kHz is a mechanical wave. The reverse, in order to prevent hitting obstacles, obstructions to the need to measure the distance between cars, which requires the use of ultrasonic sensors. Ultrasonic sensor, also known as ultrasonic transducer or ultrasonic probe. Ultrasonic sensors, including ultrasonic transmitter and ultrasonic receiver, but an ultrasonic sensor can also send and receive sound with the dual role. Ultrasonic sensors is the use of the principle of the piezoelectric effect and ultrasonic energy into each other, that is, when the ultrasonic transmitter will be transmitting ultrasonic vibrations into electrical energy; and when receiving the echo, ultrasonic vibration will be converted into electrical signals.

Generally use the principle of ultrasonic distance measurement transit time method (TOF, time offlight). Ultrasonic emission sensor ultrasonic transmitter in one direction, and began the launch time, ultrasonic propagation in the air, spread way to return immediately to encounter obstacles, the receiver receives ultrasonic waves reflected back to immediately stop the clock, to calculate the ultrasound return from launch to encounter obstacles when the time spent t, room temperature, ultrasonic velocity in the air for the V = 340 m / s, according to the formula S = V t / 2, to compute the obstructions to the ultrasound between the sensors.

2 system overall circuit

Microcontroller AT89C51 programming generated a square wave, 40 kHz through the P1.0 port output pulse signal, the ultrasonic transmitter driver circuit CD4069 amplified ultrasonic probe launched UCM40T, produce ultrasound. Obstacles encountered in communication resulting from ultrasonic echo into the receiver, receiver and transmitter probe using the probe pair UCM40R, the ultrasonic pulse becomes modulated AC voltage signal, the ultrasonic receiver circuit CX20106A processed output by 7 feet as an interrupt request signal sent to the microcontroller for processing. Square-wave emission in the SCM, while ultrasonic transmitter circuit is transmitting ultrasound at the same time open the MCU internal timer T0, fired by the timer to record the time and received ultrasonic reflection time. When the ultrasonic wave receiving circuit when the received ultrasonic reflection ultrasonic receiver circuit generates a low output INTO output to generate an interrupt request signal terminal, the microcontroller AT89C51 response to external interrupt request, the implementation of the external interrupt service routine, according to the value of the timer reading take the time difference, by the formula S = V t / 2 corresponding distance calculations and displays the results to the LED digital tube. If the S value is less than the alarm distance of 0.5 m, then the microcontroller AT89C51 it to the P2.5 port of a low-level signals, making the alarm circuit to achieve sound and light alarm.

overall system block diagram of Figure 1

3 hardware circuit

3.1 AT89C51

AT89C51 is a low voltage, high-performance CMOS 8-bit microprocessor chip contains 4 KB of Flash can be read repeatedly rewritable program memory (ROM) and 128 B of the random access data memory (RAM), with the standard MCS-51 instruction set and pin compatible 8-bit general-purpose CPU chip and built-in Flash memory cell, ATMEL The AT89C51 is a highly efficient micro-controller.

AT89C51 is a low-power high-performance microcontroller, which has 40 pins, 32 external bi-directional input / output (I / O) ports, and includes two external interrupts, two 16-bit programmable timer counter , 2 full duplex serial port.

AT89C51 can be programmed according to conventional methods can also be on-line programming. It will be a common combination of microprocessors and Flash memory, in particular, can be repeated erase the Flash memory can effectively reduce the development costs.

3.2 ultrasonic transmitter circuit

Ultrasonic transmitter circuit mainly driven by the ultrasonic transmitter circuit CD4069 and T composition. Shown in Figure 2, piezoelectric ceramic ultrasonic transducer probe UCM40T, when coupled with its two pulse signal, whose frequency is equal to the frequency of piezoelectric resonance when it will produce ultrasound. Best of ultrasound propagation in the air frequency of 40 kHz, while using a piezoelectric ceramic sensor, the driving frequency is 40 kHz, thus generated by microcontroller ports P1.0 40 kHz square wave signal, after the dual inverter deal with external ultrasonic oscillator circuit at both ends of oscillation, dual inverter can increase the drive capability, but also can enhance the received signal, suppress the other noise and interference. Ultrasonic transmitter is similar to the probe ends of the square wave generated by Sasser.

3.3 ultrasonic receiver circuit

Ultrasonic receiver circuit uses the integrated circuit CX20106A, it can be used to complete the signal amplification, limiting, band-pass filtering, peak detection and wave shaping features, the circuit shown in Figure 3. Transmitter circuit sends out pulses of signals after the obstacles encountered by the reflected ultrasonic pulse into a weak AC signal, the receiving circuit to receive and sent to CX20106A 1 foot, for the input signal, after amplification of the preamplifier , limiting amplifier of the amplification, because of its automatic gain control, can guarantee the ultrasonic sensor receives the reflected signal farther weak voltage output, the amplifier has high gain, but strong at close range when the input signal does not overload the amplifier, its center frequency of bandpass filter chip can be adjusted 5 feet of the external resistor, take 200 k, control of 38 kHz. Through the band pass filter, peak filtering, integration, finally by the shaping circuit output pulse signal.

CX20106A receiving ultrasound has high sensitivity and strong anti-interference ability to meet the requirements of ultrasonic receiver circuit. IC can also reduce the interference.

Figure 2 ultrasonic transmitter circuit

ultrasonic receiver circuit in Figure 3

3.4 sound and light alarm alarm circuit

Shown in Figure 4, the sound selection of piezoelectric buzzer alarm circuit, it takes about 10 mA of drive current. When the microcontroller output low, the transistor turns on, the buzzer alarm. Light alarm circuit shown in Figure 5, when the microcontroller output port p2.5 low, diode, light emitting light alarm signal.

sound the alarm circuit in Figure 4

Figure 5, light alarm circuit

4 Software Design

First, the microprocessor AT89C51 P1.0 first set to 0, the square wave generated by software programming, gave ultrasonic sensors, ultrasonic transmitter through the piezoelectric ceramic chip (40 kHz square wave), the delay is about 300 us (or greater than this time, this delay is to avoid a direct reflection of ultrasonic waves over the interference of the size of which determines the blind, the longer the delay, the greater the blind, 300 us delay is about 10 cm of the blind spot) inhibited Output interference and start the internal timer T0 timer. When the ultrasonic signal when the signal returns immediately encountered obstacles, and the microprocessor is constantly scanning INT0 pin INT0 if the received signal from the high to low, indicating that the signal has returned, the microprocessor interrupt process, while closing the timer T0. Then processed the data in the timer can be drawn between the ultrasonic sensor and obstacle distance show on the LED digital tube. Then under appropriate circumstances to determine whether to conduct sound and light alarm.

Program starts, the first initialization, followed by a continuous process of launching a square wave, which launched a subroutine call several times, and each launch will be in the delay period after the end of the process of waiting to determine whether there has been interrupted, that is, whether there is echo produced when echo occurs, enter the interrupt service routine, first turn off interrupt, read the timer time t, according to the time, with the ultrasonic distance measurement formula S = 340 t / 2, you can get obstacles to the distance between the ultrasonic transmitter, according to calculation, the distance to the LED digital tube display.

The same time to determine whether the distance is less than 0.5 m, if less than 0.5 m, to the sound and light alarm. Program flow chart shown in Figure 6.

Figure 6 flowchart

5 Conclusion

The system uses 51 single chip design, design a simple, easy to operate.

Tested by experiment proved that the system is stable and can meet the requirements of reversing the collision, and lower cost, with a good price. Can be applied to the car parking places.

Of ultrasound by the external environment, so there are some errors in the system, can be temperature compensation, reducing errors, and enhance system performance.

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