1. Function

The ultrasonic distance measuring learning board can be applied to the position monitoring of car reversing, construction sites and some industrial sites, as well as the measurement of liquid level, well depth and pipeline length. It is required that the measurement range is 0-27 ~ 4.00m, the measurement accuracy is 1cm, and there is no direct contact with the measured object during measurement. It can clearly and stably display the measurement results.

2. Basic principles

The internal structure of the ultrasonic generator has two piezoelectric wafers and a resonance plate. When the pulse signal is applied to its two poles and its frequency is equal to the natural oscillation frequency of the piezoelectric wafer, the piezoelectric wafer will resonate and drive the resonance plate to vibrate, which will produce ultrasonic wave. On the contrary, if no voltage is applied between the two electrodes, when the resonance plate receives the ultrasonic book, it will compress the piezoelectric wafer for vibration and convert the mechanical energy into an electrical signal, which will become an ultrasonic receiver. In the ultrasonic detection circuit, the output pulse obtained by the transmitting end is a series of square waves, and its width is the time interval of transmitting ultrasonic. The larger the distance of the measured object is, the larger the pulse width is, and the number of output pulses is directly proportional to the measured distance.

The learning board adopts STC89C51 single chip microcomputer, crystal oscillator: 12mfl ZL single chip microcomputer, P1 Port 0 outputs the 40kflz square wave signal required by the ultrasonic transducer. The external interrupt port o is used to monitor the return signal output by the ultrasonic receiving circuit. The display circuit adopts a simple 4-bit common positive led nixie tube. The code breaking is driven by 74 [S244], and the bit code is driven by 8550. It is mainly composed of single chip microcomputer system and display circuit, ultrasonic transmitting circuit and ultrasonic detection receiving circuit. STC89C51 is used to control cx201 06A infrared receiving chip and tct40-10 series ultrasonic conversion module. MCU passes P1 The O pin controls the transmission of ultrasonic wave through the inverter, and then the single chip microcomputer constantly detects the INT0 pin. When the level of lnt0 pin changes from high level to low level, it is considered that the ultrasonic wave has returned.

The data counted by the counter is the time experienced by the ultrasonic wave. Through conversion, the distance between the sensor and the obstacle can be obtained. At the same time, the experimental board supports serial port ISP online download program. If your computer does not have serial port, the board supports ljsb adapter line for ISP download, which is very convenient; The on-board lcdl602 LCD interface supports out of circuit expansion, and a 40 core out of circuit expansion interface has been reserved on the board.

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