Development of digital ultrasonic rangefinder
1, Introduction
Ultrasonic waves propagate at different speeds in gases, liquids and solids, with good directionality, concentrated energy, low attenuation during transmission and strong reflective ability. Ultrasonic waves can propagate at a certain speed in a directional manner, the formation of reflections after encountering obstacles, the use of this feature, through the determination of ultrasonic round-trip time can be calculated from the actual distance, so as to achieve non-contact measurement of the distance to the object. Ultrasonic distance measurement is rapid, convenient, and not affected by light and other factors, widely used in hydrological level measurement, building construction site measurement, site location monitoring, vehicle reversing obstacle detection, mobile machines into the detection and positioning and other fields. In this paper, the design of the digital ultrasonic rangefinder through the ultrasonic round-trip time input to the counter at a specific frequency clock pulse counting, and then display the corresponding measurement distance.
2, ultrasonic rangefinder circuit composition and working principle
Ultrasonic rangefinder by the ultrasonic generation circuit, ultrasonic receiving and amplifying circuit, counting and display circuit.
2.1 Ultrasonic generation circuit
Ultrasonic generation circuit. Dual timer EN556 (U2b) monostable trigger. R6 and C6 constitute a differential circuit, its role is: when the key S2 is pressed, the low level into positive and negative spike pulse, after VD1 to get the negative spike pulse, triggering the monostable trigger flip-flop. Monostable flip-flop output high level lasts about 1ms, that is, tw ≈ 1.1R5C5 ≈ 1ms. EN556 (U2n) composed of a polytunnel oscillator, oscillation frequency f1 = 1/T1 ≈ 1/{0.7 [(R1 + R2) + 2 (R3 + R4)] C3 ≈ 40kHz. the oscillation of the oscillator oscillation is controlled by the monostable trigger output level. When the monostable trigger outputs a high level, the polytuned oscillator generates oscillations, and pin 5 of the EN556 outputs about 40 rectangular pulses with a frequency of 40kHz and a duty cycle of about 50%. Considering the instability of the start-up phase of the multi-harmonic oscillator, the design is designed to output m a larger number of pulses. If the number of output pulses is too small, the emission intensity is small and the measurement distance is short. Humidity sensor probe , , stainless steel heater PT100 sensor , , cast aluminium heater , heating coil Fluid solenoid valve However, the number of pulses is too much, the launch duration is long, and the pulse string has not yet been launched when the distance from the object to be measured is relatively close, which results in the echo generated by the pulses launched first will arrive at the receiving end, which affects the ranging results, resulting in the increase of the ranging blind spot. 74HC04 (U1) U1a~U1e Composition of ultrasonic pulse drive circuit, can improve the drive ultrasonic transmission sensor pulse voltage amplitude, effective electrical / acoustic conversion, enhance the ability to launch ultrasonic waves, increase the measurement distance. 40kHz pulse string all the way through the U1a inverted, and then by the U1b and U1e in parallel inverter inverted; the other way through the south of the U1c and U1d inverted in parallel inverter.
