production plan of ultrasonic rangefinder

The ultrasonic rangefinder adopts NE555 circuit, two-stage amplifier circuit and level comparison circuit to realize the transmission and reception of ultrasonic waves. The comparator is the core unit of the rangefinder, which realizes the control of the transmitting circuit and the processing of the received data. This system has strong practical value and good market prospects.

　　一 The overall plan

1.1 Alternatives

　　Solution 1: Ultrasonic rangefinder is using discrete modules

The system includes five parts: ultrasonic distance measurement module, LED digital display module, drive module control module and power supply.

　　 Ultrasonic ranging module sensor is mainly composed of transmitting part and receiving part. The transmission of small ultrasonic transducer is controlled by the main controller (as shown in Figure 1); the ultrasonic transducer resonates at a frequency of 40KHz, and the module has a 40KHz square wave generating circuit.

　　 The display module is an 8-digit segment digital display LCD; the measurement result display uses a three-digit field code, the format is X points XX meters, and a two-digit segment code is used to display the number of data.

　　The power supply adopts 9V DC power input. After the voltage regulator tube, 5V and 3.3V power supplies are used for various parts of the system.

Figure 1 The structure of ultrasonic ranging sensor

　　 Scheme 2: Ultrasonic distance meter based on PIC16F876A microcontroller.

The ultrasonic rangefinder is mainly based on the single chip microcomputer PIC16F876A. Its transmitter uses the resonance of the piezoelectric crystal to drive the surrounding air to vibrate to work. The ultrasonic transmitter emits ultrasonic waves in a certain direction, and starts timing at the same time as the ultrasonic waves are in the air. Propagation, it will return immediately when it encounters an obstacle on the way, and the ultrasonic receiver will stop timing when it receives the reflected wave. Under normal circumstances, the propagation speed of ultrasonic waves in the air is 340m/s. According to the time t recorded by the timer, the distances between the launch point and the obstacle can be calculated, that is, s=340&TImes;t/2, which is commonly used time difference method for distance measurement.

In the design of the ranging counting circuit, the relevant counting method is adopted. The main principle of ultrasonic transducer sensor is the single-chip microcomputer system first provides pulse signals to the transmitter circuit during measurement, and the single-chip counter is in the waiting state and does not count; when the signal is transmitted for a period of time, the single-chip microcomputer sends the signal causes the system to shut down the transmitting signal, and the counter starts counting to achieve synchronization at the beginning; when the last pulse of the received signal arrives, the counter stops counting.

　　 The two-way ultrasonic rangefinder system mainly consists of several parts (as shown in Figure 2): LED display module, PIC16F876A chip, ultrasonic transmitter module, ultrasonic receiver module, power module and other five modules.

　Figure 2 Overall block diagram of system design

　　1.2 Scheme selection

 Since the design of this ultrasonic air transducer is digital-analog circuit design, and considering that MCU programming is not familiar to the team members, debugging will encounter greater difficulties. Scheme 1 circuits are built for the knowledge learned, and the principles are relatively familiar, so scheme 1 with more complicated hardware circuits is adopted.

　　二 Design and implementation

　　 Ultrasonic range finder is based on the characteristics of ultrasonic waves reflected back when encountering obstacles. The ultrasonic transmitter emits ultrasonic waves in a certain direction, and starts timing at the same time as the transmission. The ultrasonic waves propagate in the air and return immediately when encountering obstacles on the way. The ultrasonic receiver immediately interrupts and stops timing when the reflected waves are received. By continuously detecting the echoes reflected by obstacles encountered after the generated wave is emitted, the time difference T between the transmitted ultrasonic wave and the received echo is measured, and then the distance L is obtained. The basic ranging formula is: L=(△t/2)*C

　　 where L is the distance to be measured

　　T——the time interval between the transmitted wave and the reflected wave

　　C——The sound velocity of ultrasound in the air, which is 340m/s at room temperature

After the speed of sound is determined, L can be obtained as long as the round-trip time of the ultrasonic wave is measured.

　　2.1 Principle of Ultrasonic Ranging

　　 2.1.1 Launch part

　　 Figure 3 Ultrasonic emission structure diagram is composed of two 555 integrated circuits. IC1 (555) constitutes the ultrasonic pulse signal generator, the working cycle calculation formula is as follows, there will be some differences in the actual circuit due to errors such as components.

　　Conditions: RA =9.1MΩ, RB=150KΩ, C=0.01μF

　　TL = 0.69 x RB x C = 0.69 x 150 x 103 x 0.01 x 10-6 = 1 msec

　　TH = 0.69 x (RA + RB) x C = 0.69 x 9250 x 103 x 0.01 x 10-6 = 64 msec

　　IC2 constitutes an ultrasonic carrier signal generator. Controlled by the pulse signal output by IC1, it outputs a 1ms pulse with a frequency of 40kHz, a duty cycle of 50%, and a stop for 64ms. Calculated as follows:

　　Conditions: RA =1.5KΩ, RB=15KΩ, C=1000pF

　　TL = 0.69 x RB x C = 0.69 x 15 x 103 x 1000 x 10-12 = 10μsec

　　TH = 0.69 x (RA + RB) x C = 0.69 x 16.5 x 103 x 1000 x 10-12 = 11μsec

　　F = 1/(TL + TH) = 1/((10.35 + 11.39) x 10-6) = 46.0 KHz

IC3 (CD4069) composes the ultrasonic transmitting head drive circuit.