Single chip microcomputer of ultrasonic sensor

Views: 10 Author: Site Editor Publish Time: 2019-03-26 Origin: Site

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Ultrasound refers to mechanical waves with a frequency higher than 20 kHz. In order to use ultrasonic waves as a detecting means, it is necessary to generate ultrasonic waves and receiving ultrasonic waves. The device that performs this function is an ultrasonic sensor, which is customarily called an ultrasonic transducer or an ultrasonic probe. Ultrasonic distance measuring transducer has a transmitter and a receiver, but an ultrasonic sensor can also have the dual function of transmitting and receiving sound waves. Ultrasonic sensors use the principle of piezoelectric effect to convert electrical energy and ultrasonic waves into each other, that is, when transmitting ultrasonic waves is converting electrical energy and transmitting ultrasonic waves; and when is receiving echoes, converting ultrasonic vibrations into electricity signal.

The principle of ultrasonic ranging transducer generally uses the time of flight (TOF). First, measure the time for the ultrasonic wave to return from the launch to the obstacle, and multiply the speed of the ultrasonic wave to get twice the distance between the sound source and the obstacle.

This ultrasonic distance sensor circuit is a sensor that integrates transmission and reception. Inside the sensor is a circular sheet of plastic material with a metal film on the front and an aluminum back plate on the back. The sheet and the back plate constitutes a capacitor. When a square wave voltage having a frequency of 49.4 kHz and a voltage of 300 VAC pk-pk is applied to the sheet, the sheet vibrates at the same frequency to generate ultrasonic waves having a frequency of 49.4 kHz. When receiving echoes, a tuning circuit allows only signals with frequencies approaching 49.4 kHz to be received, while signals at other frequencies are filtered. The ultrasonic waves transmitted by the ultrasonic sensor have a beam angle of 30 degrees.

The ultrasonic sensor can be used as both a transmitter and a receiver. The sensor emits a series of ultrasonic beams for a period of time. The reception can be started only after the transmission is completed. The time for transmitting the beam is D, which is reflected back from the object in D time. The signal can not be captured; in addition, the ultrasonic sensor has a certain inertia, and there is still a certain residual vibration after the end of the transmission. This residual vibration also generates a voltage signal through the transducer, which disturbs the system to capture the return signal. Therefore, before the residual vibration has disappeared, the system cannot start the echo reception. The two reasons cause the ultrasonic sensor to measure a certain measurement range. This ultrasound can measure 37cm recently.

The TL851 is an economical digital 12-step ranging control IC. There is a 420KHz ceramic crystal oscillator inside. When the ultrasonic range finding sensor starts working, the ceramic crystal oscillator is divided by 8.5 in the first 16 cycles of transmission to form an ultrasonic signal of 49.4KHz, which is then sent to the ultrasonic sensor through the transistor Q1 and the transformer T1. . After the transmission, the ceramic crystal oscillator is divided by 4.5 for the timing of the microcontroller. The TL852 is a chip designed specifically for receiving ultrasound. Because the ultrasonic signal is relatively weak, it needs to be amplified to be received by the MCU. The TL852 mainly provides an amplifying circuit. When the TL852 receives 4 pulse signals, it sends a high level to the TL851 through the REC to indicate that the ultrasonic wave has been received.

This system uses microcontroller to realize the control of Polaroid 600 series sensor and Polaroid 6500 series ultrasonic distance module. The MCU controls the transmission of the ultrasonic wave through the inverter through the P1.0 pin, and then the MCU continuously detects the INT0 pin. When the level of the INT0 pin changes from high level to low level, the ultrasonic wave is considered to return. The data counted by the counter is the time elapsed by the ultrasonic wave, and the distance between the sensor and the obstacle can be obtained by conversion. The hardware schematic diagram of ultrasonic distance measuring transducer is shown. During operation, the microprocessor first sets activates the ultrasonic sensor to transmit ultrasonic waves, and starts the internal timer T0 to start timing. Since the ultrasonic sensor we use is integrated and transmitted, the ultrasonic sensor has aftershocks after 16 pulses have been transmitted. In order to eliminate the transmission signal of the ultrasonic sensor from the return signal identification, it is necessary to detect the return signal after 2.38 ms after starting the transmission signal. so that the output interference can be suppressed. When the ultrasonic signal hits the obstacle, the signal returns immediately, and the microprocessor continuously scans the INT0 pin. If the signal received by INT0 changes from high level to low level, it indicates that the signal has returned and the microprocessor enters the interrupt. Then the data in the timer can be converted to obtain the ultrasonic sensor and obstacles.

Ultrasonic distance measuring transducer circuit design ultrasonic directivity is strong, energy consumption is slow, and the distance traveled in the medium is far. Therefore, ultrasonic waves are often used for distance measurement. For example, rangefinder and level measuring instrument can realize low frequency 400Hz HID by ultrasonic wave. The module is a simple solution for designing gas discharge lamp power supply. module support HID lamp energy-saving electronic ballast is no longer cumbersome. With your support, you will be provided with more finished products for you.

Due to the strong directivity of the ultrasonic waves, the energy consumption is slow, and the distance traveled in the medium is long. Therefore, ultrasonic waves are often used for distance measurement, such as range finder and level measuring instrument, which can be realized by ultrasonic waves. The use of ultrasonic testing is often quick, convenient, simple to calculate, easy to achieve real-time control, and can meet industrial and practical requirements in terms of measurement accuracy, so it has also been widely used in the development of mobile robots.In order to automatically avoid obstacles, it is necessary to equip the ranging system to obtain the distance information (distance and direction) from the obstacle in time. The three-direction (front, left, and right) ultrasonic ranging systems described provide a distance information for the robot to understand the environment in front, left, and right.