A Brief Overview of the Ultrasonic Range Finder's Composition and Structure
The ultrasonic range finder is composed of ultrasonic generating circuit, ultrasonic receiving and amplifying circuit, counting and displaying circuit.
The ultrasonic generating circuit is an ultrasonic generating circuit. Dual timer EN556 (U2b) constitutes a monostable flip-flop. R6 and C6 form a differential circuit, and its function is: when the button S2 is pressed, the low level becomes a positive and negative peak pulse, and a negative peak pulse is obtained through VD1, triggering the flip-flop of the monostable flip-flop. The high level of the monostable flip output lasts for about 1 ms, that is, tw≈1. 1R5C5≈1 ms. EN556 (U2n) forms a multivibrator, and the oscillation frequency f1=1/T1≈1/{0.7[(R1+R2)+2(R3+R4)]C3≈40 kHz. The oscillator oscillation is controlled by the monoflop output level. When the monostable trigger outputs a high level, the multivibrator oscillates, and pin 5 of the EN556 outputs about 40 rectangular pulses with a frequency of 40 kHz and a duty cycle of about 50%. Taking into account the instability of the multivibrator start-up phase, so the number of input m pulses is designed to be more. If the number of output pulses is too small, the emission intensity will be small and the measurement distance will be short. However, the number of pulses is too many, and the transmission duration is long. When the distance to the measured object is relatively close, the pulse train has not been transmitted, so that the echo generated by the pulse transmitted first will reach the receiving end, which will affect the distance measurement result and cause distance measurement. The dead zone increases. U1a~U1e of (U1) form an ultrasonic pulse drive circuit, which can increase the amplitude of the pulse voltage driving the ultrasonic sending sensor, effectively perform electrical/acoustic conversion, enhance the ability to emit ultrasonic waves, and increase the measurement distance. One path of the 40 kHz pulse train is inverted by U1a, and then inverted by the parallel inverter of U1b and U1e; the other path is inverted by the parallel inverter of U1c and U1d.
